U.S. patent application number 09/122644 was filed with the patent office on 2001-12-27 for ip over atm system using control messages to set up cut-through paths or bypass pipes in routers.
Invention is credited to AMI, JUNKO, ESAKI, HIROSHI, KATSUBE, YASUHIRO, NAGAMI, KENICHI, SAITO, TAKESHI.
Application Number | 20010056490 09/122644 |
Document ID | / |
Family ID | 26399263 |
Filed Date | 2001-12-27 |
United States Patent
Application |
20010056490 |
Kind Code |
A1 |
NAGAMI, KENICHI ; et
al. |
December 27, 2001 |
IP OVER ATM SYSTEM USING CONTROL MESSAGES TO SET UP CUT-THROUGH
PATHS OR BYPASS PIPES IN ROUTERS
Abstract
A packet transfer scheme in a network system capable of
realizing a high speed, large capacity inter-network communication
under an internet environment. A network interconnection apparatus
(router) has a memory for storing a correspondence relationship
between a virtual connection used in receiving a packet from one
logical network and a virtual connection used in transmitting a
packet to another logical network, and a transfer at a datalink
layer is carried out according to the registered correspondence
relationship, to effectively form a bypass pipe capable of
transferring a packet by an datalink layer level processing alone
over a plurality of networks from the transmission terminal to the
destination terminal, so that a high speed packet transfer between
networks can be realized.
Inventors: |
NAGAMI, KENICHI; (CHIBA-KEN,
JP) ; AMI, JUNKO; (KANAGAWA-KEN, JP) ;
KATSUBE, YASUHIRO; (KANAGAWA-KEN, JP) ; SAITO,
TAKESHI; (TOKYO, JP) ; ESAKI, HIROSHI;
(KANAGAWA-KEN, JP) |
Correspondence
Address: |
FOLEY & LARDNER
WASHINGTON HARBOUR
3000 K STREET NW SUITE 500
P O BOX 25696
WASHINGTON
DC
200078696
|
Family ID: |
26399263 |
Appl. No.: |
09/122644 |
Filed: |
July 27, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09122644 |
Jul 27, 1998 |
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08924825 |
Sep 5, 1997 |
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5835710 |
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08924825 |
Sep 5, 1997 |
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08522115 |
Aug 31, 1995 |
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Current U.S.
Class: |
709/227 ;
370/397; 709/250 |
Current CPC
Class: |
H04L 2012/5667 20130101;
H04L 2012/562 20130101; H04Q 11/0478 20130101; H04L 12/4608
20130101 |
Class at
Publication: |
709/227 ;
709/250; 370/397 |
International
Class: |
G06F 015/16; H04L
012/28; H04L 012/56 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 1994 |
JP |
P06-232092 |
Feb 23, 1995 |
JP |
P07-58196 |
Aug 31, 1994 |
JP |
P06-232092 |
Feb 23, 1995 |
JP |
P07-058196 |
Claims
What is claimed is:
1. A network interconnection apparatus for connecting at least two
virtual connection-oriented logical networks, comprising: physical
interface means for interfacing the logical networks; first
transfer means for applying a network layer level processing to a
packet received from one logical network and transmitting the
packet to another logical network; memory means for storing a
correspondence relationship between a virtual connection used in
receiving a packet from said one logical network and a virtual
connection used in transmitting the packet to said another logical
network; second transfer means for carrying out a packet transfer
without the network layer level processing, according to the
correspondence relationship stored in the memory means; and
registration means for receiving a control message containing
information for a registration of the correspondence relationship
from at least one of the logical networks, and registering the
correspondence relationship into the memory means according to the
control message.
2. The apparatus of claim 1, wherein the memory means also stores
an information indicating whether a packet transfer by the first
transfer means is to be carried out with respect to a virtual
connection used in receiving the packet from said one logical
network.
3. The apparatus of claim 1, further comprising storage means for
storing information for identifying virtual connections formed
between the network interconnection apparatus and other nodes; and
reception means for receiving the packet transferred from said one
logical network; wherein the first transfer means determines a next
transfer target node by analyzing a destination node information
contained in the packet received-by the reception means at a
network layer level, specifies a virtual connection formed between
the next transfer target node and the network interconnection
apparatus according to the storage means, and transfers the packet
through the specified virtual connection, when the correspondence
relationship for a virtual connection used in receiving the packet
is not stored in the memory means; and the second transfer means
carries out the packet transfer without the network layer level
processing according to the correspondence relationship stored in
the memory means when the correspondence relationship for a virtual
connection used in receiving the packet is stored in the memory
means.
4. The apparatus of claim 3, wherein the registration means
analyzes the information contained in the control message
transferred from one node, selects a virtual connection formed
between another node and the network interconnection apparatus
according to the storage means, and registers the correspondence
relationship between the selected virtual connection and a virtual
connection obtained by analyzing the control message.
5. The apparatus of claim 3, wherein the control message is a
signaling packet, and the registration means analyzes the
information contained in the signaling packet transferred from one
node through a signaling processing means, receives a virtual
connection formed between another node and the network
interconnection apparatus which is allocated by the signaling
processing means, and registers the correspondence relationship
between the allocated virtual connection and a virtual connection
obtained by analyzing the signaling packet, where the signaling
processing means carries out a signaling processing to allocate a
virtual connection between two nodes and transmit the signaling
packet containing an identification information for the allocated
virtual connection to said two nodes.
6. The apparatus of claim 1, wherein a packet transfer by the first
transfer means is switched to a packet transfer by the second
transfer means when the registration means registers the
correspondence relationship into the memory means.
7. The apparatus of claim 1, wherein a packet transfer by the first
transfer means is switched to a packet transfer by the second
transfer means when a notice indicating a set up of a bypass pipe
connecting virtual connections up to a destination node is
received.
8. The apparatus of claim 1, further comprising: control message
transmission means for transmitting another control message to a
next stage network interconnection apparatus, said another control
message containing information for a registration of a
correspondence relationship at the next stage network
interconnection apparatus.
9. The apparatus of claim 8, wherein the control message
transmission means transmits said another control message according
to a statistical information regarding a transfer of the packet to
be transferred by the network interconnection apparatus.
10. The apparatus of claim 8, wherein the control message
transmission means transmits said another control message when the
next stage network interconnection apparatus is a activated.
11. The apparatus of claim 8, wherein the control message
transmission means transmits said another control message when the
network interconnection apparatus receives the packet to be
transferred from a first node belonging to said one logical network
to a second node belonging to said another logical network.
12. A network node apparatus directly connected with one virtual
connection-oriented logical network, for transmitting packets to a
node connected with another virtual connection-oriented logical
network, comprising: physical interface means for interfacing the
logical networks; memory means for storing a correspondence between
a destination node information for each packet to be transmitted
and a virtual connection to be used in transmitting each packet;
first transmission means for transmitting the packet according to
the correspondence stored in the memory means; and second
transmission means for transmitting a control message to a network
interconnection apparatus connecting said one logical network and
said another logical network, the control message containing
information for a registration of a correspondence relationship
between a first virtual connection used in receiving a packet from
said one logical network and a second virtual connection used in
transmitting the packet to said another logical network.
13. The apparatus of claim 12, further comprising: update means for
updating the correspondence stored in the memory means according to
an information on the first virtual connection contained in the
control message.
14. The apparatus of claim 13, wherein the update means updates the
correspondence stored in memory means after the second transmission
means transmits the control message.
15. The apparatus of claim 13, wherein the update means updates the
correspondence stored in memory means when a notice indicating a
set up of a bypass pipe connecting the first virtual connection and
the second virtual connection is returned from the network
interconnection apparatus to which the control message is
transmitted by the second transmission means.
16. The apparatus of claim 12, further comprising: storage means
for storing an identification information for a virtual connection
formed between the network node apparatus and the network
interconnection apparatus, the identification information being
unique in said one logical network; wherein the second transmission
means transmits the control message containing the identification
information of a virtual connection selected according to the
storage means and an information for specifying source and
destination nodes of each packet to be transmitted.
17. The apparatus of claim 12, wherein the second transmission
means transmits the control message according to a statistical
information regarding a transfer of the packet to be transferred by
the network interconnection apparatus.
18. The apparatus of claim 12, wherein the second transmission
means transmits the control message when a next stage network
interconnection apparatus is activated.
19. The apparatus of claim 12, wherein the second transmission
means transmits the control message when the network node apparatus
receives the packet to be transferred from a first node belonging
to said one logical network to a second node belonging to said
another logical network.
20. A method of packet transfer for transferring a packet
transmitted from a first node belonging to one logical network to a
second node belonging to another logical network, comprising the
steps of: determining a correspondence relationship between a
virtual connection available for transmitting the packet from the
first node and a virtual connection available for transmitting the
packet to the second node, according to a control message
containing an identification information for a desired virtual
connection available for transmitting the packet without a network
layer level processing over different logical networks, the control
message being transmitted from at least one of the first and second
nodes; storing the correspondence relationship determined at the
determining step in a memory; and transferring a newly received
packet without carrying out a network layer level analysis
according to the correspondence relationship when the
correspondence relationship for a virtual connection used in
receiving the newly received packet is stored in the memory.
21. The method of claim 20, further comprising the steps of:
deleting the correspondence relationship from the memory when the
control message is not transmitted regularly; and transferring a
newly received packet by carrying out the network layer level
analysis when the correspondence relationship for a virtual
connection used in receiving the newly received packet is not
stored in the memory.
22. The method of claim 20, wherein the control message is either
one of a set up request message and a release request message, and
the storing step stores the correspondence relationship when the
control message is the set up request message, and the method
further comprises the steps of: deleting the correspondence
relationship from the memory when the control message is the
release request message; and transferring a newly received packet
by carrying out the network layer level analysis when the
correspondence relationship for a virtual connection used in
receiving the newly received packet is not stored in the
memory.
23. The method of claim 20, wherein the control message contains an
identification information for a first virtual connection available
for transmitting the packet from one of the first node and the
second node to a network interconnection apparatus interconnecting
said one logical network and said another logical network, in
addition to the identification information for the desired virtual
connection, and the method further comprises the steps of:
transmitting the control message from said one of the first node
and the second node to the network interconnection apparatus
through a second virtual connection different from the first
virtual connection; and analyzing the control message and forming a
bypass pipe connecting the first virtual connection with a virtual
connection connected to a logical network to which another one of
the first node and the second node belongs.
24. The method of claim 20, wherein the control message is a
signaling packet which contains an identification information for a
first virtual connection available for transmitting the packet from
one of the first node and the second node to a network
interconnection apparatus interconnecting said one logical network
and said another logical network, in addition to the identification
information for the desired virtual connection, and the method
further comprises the steps of: transmitting the control message
from said one of the first node and the second node to the network
interconnection apparatus through a virtual connection for a
signaling which is different from the first virtual connection; and
applying a signaling processing to the control message, and forming
a bypass pipe connecting the first virtual connection with a
virtual connection connected to a logical network to which another
one of the first node and the second node belongs.
25. The method of claim 20, further-comprises the steps of:
transmitting the control message from one of the first node and the
second node to a network interconnection apparatus interconnecting
said one logical network and said another logical network through
one virtual connection; forming a bypass pipe connecting said one
virtual connection with a virtual connection connected to a logical
network to which another one of the first node and the second node
belongs.
26. The method of claim 20, wherein the control message is
transmitted according to a statistical information regarding a
transfer of the packet to be transferred by a network
interconnection apparatus interconnecting said one logical network
and said another logical network.
27. The method of claim 20, wherein the control message is
transmitted when a next stage network interconnection apparatus is
activated.
28. The method of claim 20, wherein the control message is
transmitted when the packet to be transferred from the first node
to the second node is received by a network interconnection
apparatus interconnecting said one logical network and said another
logical network.
29. A network interconnection apparatus for connecting at least two
virtual connection-oriented logical networks, comprising: physical
interface means for interfacing the logical networks; first
transfer means for applying a network layer level processing to a
packet received from one logical network and transmitting the
packet to another logical network; memory means for storing a
correspondence relationship between a virtual connection used in
receiving the packet from said one logical network and a virtual
connection used in transmitting the packet to said another logical
network; second transfer means for carrying out a packet transfer
without the network layer level processing, according to the
correspondence relationship stored in the memory means; and means
for detecting a virtual connection used in receiving the packet and
a virtual connection used in transmitting the packet at a time of a
packet transfer by the first transfer means, and registering the
correspondence relationship into the memory means according to the
detected virtual connections.
30. The apparatus of claim 29, wherein the memory means also stores
an information indicating whether a packet transfer by the first
transfer means is to be carried out with respect to a virtual
connection used in receiving the packet from said one logical
network.
31. A method of packet transfer for transferring a packet
transmitted from a first node belonging to one logical network to a
second node belonging to another logical network, comprising the
steps of: receiving a packet containing a destination node
information transmitted through a first virtual connection
available for transmitting the packet from the first node;
analyzing the destination node information contained in the packet
at a network layer level, and determining a second virtual
connection available for transmitting the packet to the second
node; transmitting the packet through the second virtual
connection, while storing a correspondence relationship between the
first virtual connection used in receiving the packet and the
second virtual connection used in transmitting the packet in a
memory; and transferring a newly received packet without carrying
out a network layer level analysis according to the correspondence
relationship when the correspondence relationship for a virtual
connection used in receiving the newly received packet is stored in
the memory.
32. A network system, comprising: a plurality of virtual
connection-oriented logical networks: a plurality of network nodes
connected to the logical networks, the nodes include terminal nodes
and network interconnection apparatuses interconnecting the logical
networks, each network interconnection apparatus has a memory means
for storing a correspondence relationship between a virtual
connection available for transmitting a packet from one network
node and a virtual connection available for transmitting the packet
to another network node, and each network interconnection apparatus
transfers a newly received packet without carrying out a network
layer level analysis when a correspondence relationship for a
virtual connection used in receiving the newly received packet is
stored in the memory means, whereas each network interconnection
apparatus transfers the newly received packet by carrying out the
network layer level analysis when the correspondence relationship
for a virtual connection used in receiving the newly received
packet is not stored in the memory means; wherein each network node
belonging to one logical network and wishing to transfer the packet
to another network node belonging to another logical network
transmits a control message containing an identification
information for a desired virtual connection available for
transmitting the packet without a network layer level processing
over different logical networks, according to which each network
interconnection apparatus connected between said one logical
network and said another logical network updates the connection
relationship stored in the memory means.
33. The system of claim 32, wherein each network interconnection
apparatus connected between said one logical network and said
another logical network also transmits the control message to a
next stage network interconnection apparatus.
34. A network system, comprising: a plurality of virtual
connection-oriented logical networks; a plurality of network nodes
connected to the logical networks, the network nodes include
terminal nodes and network interconnection apparatuses
interconnecting the logical networks, each network interconnection
apparatus has a memory means for storing a correspondence
relationship between a first virtual connection available for
transmitting a packet from one network node and a second virtual
connection available for transmitting the packet to another network
node, and each network interconnection apparatus transfers a newly
received packet without carrying out a network layer level analysis
when a correspondence relationship for a virtual connection used in
receiving the newly received packet is stored in the memory means,
whereas each network interconnection apparatus transfers the newly
received packet by carrying out the network layer level analysis
when the correspondence relationship for a virtual connection used
in receiving the newly received packet is not stored in the memory
means; wherein when each network interconnection apparatus receives
the newly received packet transmitted through the first virtual
connection, each network interconnection apparatus analyzes a
destination node information contained in the newly received packet
at a network layer level and determine the second virtual
connection to update the connection relationship stored in the
memory means.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a network interconnection
apparatus, a network node apparatus, and a packet transfer method
suitable for an internet environment formed by connection-oriented
networks.
[0003] 2. Description of the Background Art
[0004] In recent years, due to increasing demands for a variety of
communications such as an image communication and a high speed data
communication, there is an eager expectation for a realization of
the B-ISDN (Broadband-Integrated Service Digital Network) in order
to provide highly efficient and flexible communication services,
and the ATM (Asynchronous Transfer Mode) exchange scheme is
considered as a prospective scheme for actually realizing the
B-ISDN. This ATM exchange scheme is a scheme for realizing the
communication service by loading data into a fixed length packet
called cell regardless of the attributes of the data, and using
this cell as a unit of exchange. The ATM communication technique is
now studied extensively as a platform for realizing a multi-media
communication and a high speed, large capacity communication, in a
field of the public network (B-ISDN) as well as in a field of the
LAN (Local Area Network).
[0005] Now, in the conventional LAN environment such as that of the
Ethernet, the inter-LAN connection, i.e., the inter-networking
among the LANs, has been realized by providing a router between
each adjacent LANs. The main function of this router is the routing
processing for the datagram transmission over the LANs, by
processing up to the layer 3 (network layer) in the OSI (Open
System Interconnection) protocol layer stack. Namely, for the
datagram to be transmitted over two LANs, the datagram must be
brought up to the layer 3 by the router to analyze the destination
network layer address there, and then delivered to the destination
LAN according to the result of this analysis. Here, it should be
noted that, this "router" is often also referred as "gate-way" in
the field of the computer communication, but a term "gate-way" is
formally defined as an element which carries out the processing up
to the layer 7 in the OSI, so that "gate-way" is actually different
from the "router" strictly speaking.
[0006] There is also an element called "bridge" which has the
similar function as the router in realizing the inter-LAN
connection. In this bridge, in contrast to the router which
determines the destination LAN by analyzing the destination network
layer address, the destination LAN is determined by analyzing the
datalink layer address (MAC address). Namely, the bridge realizes
the inter-LAN connection by analyzing the destination MAC address
of the datagram and passing the datagram through to another LAN
when the obtained MAC address is not destined within its own LAN.
Thus, in the bridge, only the filtering of data is carried out and
the functions of the network layer are not realized.
[0007] Furthermore, there is also a similar element called
"brouter" which has the function of the router as well as the
function of the bridge. Namely, this brouter functions as the
router for the predetermined network layer protocol and as the
bridge for all the other protocols. In other words, in the brouter,
those that can be handled by the router are all handled by the
router function, while those that cannot be handled by the router
are handled by the bridge function.
[0008] The function of the router, bridge, or brouter has been
usually realized by the workstation (WS). Namely, the function of
the router, bridge, or brouter has been realized as the CPU
provided within the WS carries out the address analysis and
transmits the datagram to the allocated physical port.
[0009] Now, one of the features of the ATM communication scheme is
its high speed operation realized by the hardware switching of the
ATM cells. That is, in the ATM communication scheme, the virtual
connection (VC) or the virtual path (VP) is set up end-to-end,
while the data to be exchanged end-to-end is loaded in the payload
section of the ATM cell, and the ATM cell is exchanged and
transmitted up to the destination terminal by the hardware
switching operation alone without the intervention of the software
operation, where the hardware switching operation is carried out by
the ATM switch according to the VPI/VCI (Virtual Path
Identifier/Virtual Channel Identifier) or the value of the other
field such as PT in the ATM cell header which is contained in the
ATM cell header.
[0010] From this point of view, the ATM communication scheme can be
considered as a communication scheme which achieves its high speed
operation by referring only to the ATM cell headers, setting up the
virtual connections/paths end-to-end according to the ATM cell
header values, and carrying out the hardware switching. In a case
of applying this ATM communication scheme to the LAN, it is
considered that the communications between the terminals in the LAN
are realized by the communications through the ATM-VC/ATM-VP as
described above, and it is possible to expect a drastic speed up
and capacity increase for the communications between the
terminals.
[0011] However, in a case of the ATM-LAN, when the inter-LAN
communication is to be carried out, the network layer transfer is
carried out at the router between the LANs, so that the inter-LAN
communication has a problem in that the speed and the capacity of
the communication can be considerably lowered compared with the
communication within the LAN. In addition, due to the processing
overhead at the network, there has also been a problem that the
probability for the occurrence of the congestion becomes high as a
result of the lowering of the transfer speed and the limitation of
the processing speed.
[0012] On the other hand, the inter-networking scheme used in the
conventional data network is the connection-less scheme, in which
the data unit (network layer service data unit) transmitted to the
router by using the datalink is applied with the OSI layer 3
processing at the router, and then the relaying of the data unit is
carried out. As described above, the bridge for carrying out the
filtering of the data unit of the datalink layer only carries out
the filtering of the data unit and the functions of the network
layer are not realized.
[0013] Recently, there are propositions for the inter-networking
not only in the connection-less mode but also in the
connection-oriented mode as well. In short, these propositions
introduce the concept of the connection into the inter-networking
at the datalink level or the internetworking at the network layer
level. The ATM is a prime example of the former type, while the
ST-II recently proposed as the connection-oriented network layer
protocol is an example of the latter type.
[0014] In the ATM, the reservation of the communication resource is
made at the datalink level, while in the ST-II, the reservation of
the communication resource is made at the network layer level. In
either case, the set up of the connection is carried out before the
communication, so that they are basically the connection-oriented
schemes. Here, for the connection-less communication, the
processing of the network layer is carried out at the server (CLS,
router, etc.) of the connection-less communication, whereas for the
connection-oriented communication, the header information rewriting
table necessary for the reservation of the communication resource
and the relaying is set up before the start of the communication,
and then the actual data transfer is handled by the relaying at the
datalink level.
[0015] However, the currently available usual applications realize
the connection-oriented communication on the connection-less
service, such that the data unit is transferred by using the
connection-less communication mode even for the connection-oriented
communication. In the connection-less mode, a plurality of
processings of the network layer are carried out, and it is common
to reconstruct the data unit of the network layer in this case.
Consequently, even in the application which is designed to realize
a high speed communication by carrying out the relaying at the
datalink level, there has been a problem that the probability for
the occurrence of the congestion becomes high as a result of the
lowering of the transfer speed and the limitation of the processing
speed due to the processing overhead at the network.
SUMMARY OF THE INVENTION
[0016] It is therefore an object of the present invention to
provide a network interconnection apparatus, a network node
apparatus, and a packet transfer method, capable of realizing a
high speed, large capacity inter-network communication under an
internet environment in which a plurality of networks are
inter-networked.
[0017] According to one aspect of the present invention there is
provided a network interconnection apparatus for connecting at
least two virtual connection-oriented logical networks, comprising:
physical interface means for interfacing the logical networks;
first transfer means for applying a network layer level processing
to a packet received from one logical network and transmitting the
packet to another logical network; memory means for storing a
correspondence relationship between a virtual connection used in
receiving a packet from said one logical network and a virtual
connection used in transmitting the packet to said another logical
network; second transfer means for carrying out a packet transfer
without the network layer level processing, according to the
correspondence relationship stored in the memory means; and
registration means for receiving a control message containing
information for a registration of the correspondence relationship
from at least one of the logical networks, and registering the
correspondence relationship into the memory means according to the
control message.
[0018] This aspect of the present invention defines a first
configuration of a router (network interconnection apparatus)
according to the present invention. In transferring a data packet
from a transmission terminal belonging to one logical network to a
destination terminal belonging to another logical network, this
data packet passes through a router connecting these logical
networks. A conventional router has a rather slow transfer speed as
it transmits a packet received from one logical network to another
logical network by applying a network layer level processing. In
contrast, a router of the present invention has memory means for
storing a correspondence relationship between a virtual connection
used in receiving a packet from one logical network and a virtual
connection used in transmitting a packet to another logical
network, and a necessary correspondence relationship is registered
into this memory means according to an explicit control message
received from one logical network. Then, a transfer at a datalink
layer is carried out according to the registered correspondence
relationship, to effectively form a bypass pipe capable of
transferring a packet by a datalink layer level processing alone
over a plurality of networks from the transmission terminal to the
destination terminal, so that a high speed packet transfer between
networks can be realized.
[0019] In the router of the present invention, when a packet is
received from one logical network, if the correspondence
relationship for a virtual connection used in receiving this packet
is in the memory means, the packet is transferred to another
logical network by the second transfer means for carrying out a
transfer processing at a datalink layer level alone, whereas
otherwise the packet is transferred to another logical network by
the first transfer means for carrying out a transfer processing at
a network layer level.
[0020] Alternatively, it is also possible to provide additional
information regarding whether a transfer by the first transfer
means is to be carried out for a virtual connection used in
receiving the packet from one logical network, such that the
transfer by the first transfer means is carried out if this
additional information indicates that the transfer by the first
transfer means is to be carried out for a virtual connection used
in receiving this packet, whereas otherwise the transfer by the
second transfer means is carried out according to the
correspondence relationship stored in the memory means.
[0021] According to another aspect of the present invention there
is provided a network node apparatus directly connected with one
virtual connection-oriented logical network, for transmitting
packets to a node connected with another virtual
connection-oriented logical network, comprising: physical interface
means for interfacing the logical networks; memory means for
storing a correspondence between a destination node information for
each packet to be transmitted and a virtual connection to be used
in transmitting each packet; first transmission means for
transmitting the packet according to the correspondence stored in
the memory means; and second transmission means for transmitting a
control message to a network interconnection apparatus connecting
said one logical network and said another logical network, the
control message containing information for a registration of a
correspondence relationship between a first virtual connection used
in receiving a packet from said one logical network and a second
virtual connection used in transmitting the packet to said another
logical network.
[0022] This aspect of the present invention defines a configuration
of a network node (encompassing a terminal as well as an
intermediate stage router) according to the present invention. The
network node which transmits a packet to the router has memory
means for storing a correspondence relationship between a
destination node information of the packet and a virtual connection
to be used in transmitting the packet, and updates this memory
means after the control message is transmitted, so that an initial
setting to transfer the packet to the destination node by the
transfer processing at a network layer level in the router can be
switched to a setting to transfer the packet to the destination
node by the transfer processing at a datalink layer level alone,
i.e., a bypass pipe, in the router.
[0023] Here, the control message can contain an information for
specifying source and destination nodes of each packet to be
transmitted, which is an example of a globally unique bypass pipe
ID.
[0024] Also, the update of the memory means at the network node can
be carried out at a time of transmitting the control message, or at
a time of receiving a response message from the router notifying a
set up of the bypass pipe.
[0025] Also, in a case of using an identical virtual connection for
a transmission of the control message and a transmission of a
packet such that the router registers the correspondence
relationship by regarding this virtual connection used in receiving
the control message as a virtual connection used in receiving the
packet, the switching from the first transfer means to the second
transfer means is going to be made at the router even when the
update of the memory means at the transmission terminal side is not
carried out.
[0026] According to another aspect of the present invention there
is provided a method of packet transfer for transferring a packet
transmitted from a first node belonging to one logical network to a
second node belonging to another logical network, comprising the
steps of: determining a correspondence relationship between a
virtual connection available for transmitting the packet from the
first node and a virtual connection available for transmitting the
packet to the second node, according to a control message
containing an identification information for a desired virtual
connection available for transmitting the packet without a network
layer level processing over different logical networks, the control
message being transmitted from at least one of the first and second
nodes; storing the correspondence relationship determined at the
determining step in a memory; and transferring a newly received
packet without carrying out a network layer level analysis
according to the correspondence relationship when the
correspondence relationship for a virtual connection used in
receiving the newly received packet is stored in the memory.
[0027] This aspect of the present invention defines a method for
forming a bypass pipe by using a control message according to the
present invention. This method encompasses the following three
cases.
[0028] The first case (out-band, packet) is that in which the
control message (which is a type of packet) contains an
identification information (VCID, or VCI when a VP directly
connecting neighboring routers is provided) for a first virtual
connection available for transmitting the packet from one of the
first node and the second node to the router, in addition to the
identification information (bypass pipe ID) for the desired virtual
connection, and this control message is transmitted from said one
of the first node and the second node to the router through a
second virtual connection different from the first virtual
connection. Then, the control message is analyzed at a network
layer level, to form a bypass pipe connecting the first virtual
connection and a virtual connection connected to a logical network
to which another one of the first node and the second node belongs,
at the router.
[0029] Here, the bypass pipe ID is an identification information
unique in an entire network system containing a plurality of
logical network, and can be given by an information specifying a
transmission terminal and a destination terminal for example. On
the other hand, the VCID, or VCI when a VP directly connecting
neighboring routers is provided, is an identification information
unique within a logical network to which the transmission terminal
belongs.
[0030] The second case (out-band, ATM signaling) is that in which
the control message (ATM signaling) contains an identification
information (VCID, or VCI when a VP directly connecting neighboring
routers is provided) for a first virtual connection available for
transmitting the packet from one of the first node and the second
node to the router, which is a usual part of the ATM signaling
message, in addition to the identification information (bypass pipe
ID) for the desired virtual connection, and this control message is
transmitted from said one of the first node and the second node to
the router through a virtual connection for an ATM signaling which
is different from the first virtual connection. Then, an ATM
signaling processing is applied to the control message, to form a
bypass pipe connecting the first virtual connection and a virtual
connection connected to a logical network to which another one of
the first node and the second node belongs, at the router.
[0031] The third case (in-band) is that in which the control
message (which is a type of packet) contains the identification
information (bypass pipe ID) for the desired virtual connection,
and this control message is transmitted from one of the first node
and the second node to the router through one virtual connection.
Then, a bypass pipe connecting said one virtual connection and a
virtual connection connected to a logical network to which another
one of the first node and the second node belongs is formed at the
router.
[0032] According to another aspect of the present invention there
is provided a network interconnection apparatus for connecting at
least two virtual connection-oriented logical networks, comprising:
physical interface means for interfacing the logical networks;
first transfer means for applying a network layer level processing
to a packet received from one logical network and transmitting the
packet to another logical network; memory means for storing a
correspondence relationship between a virtual connection used in
receiving the packet from said one logical network and a virtual
connection used in transmitting the packet to said another logical
network; second transfer means for carrying out a packet transfer
without the network layer level processing, according to the
correspondence relationship stored in the memory means; and means
for detecting a virtual connection used in receiving the packet and
a virtual connection used in transmitting the packet at a time of a
packet transfer by the first transfer means, and registering the
correspondence relationship into the memory means according to the
detected virtual connections.
[0033] This aspect of the present invention defines a second
configuration of a router (network interconnection apparatus)
according to the present invention. Here, just as in the first
configuration described above, this router forms a bypass pipe
capable of transferring a packet by a datalink layer level
processing alone over a plurality of networks from the transmission
terminal to the destination terminal, so that a high speed packet
transfer between networks can be realized. The first configuration
uses the control message so that it is possible to form a bypass
pipe in a manner fully accounting for each request from a user or
an application, while this second configuration registers the
necessary correspondence relationship into the memory means
according to an information on a virtual connection obtained at a
time of transferring a packet by applying a network layer level
processing, and a transfer processing is switched from a transfer
by a network layer level processing to a transfer by a datalink
layer level processing alone once the correspondence relationship
is registered in the memory means, so that a bypass pipe for a high
speed transfer can be set up without using a special message.
[0034] According to another aspect of the present invention there
is provided a method of packet transfer for transferring a packet
transmitted from a first node belonging to one logical network to a
second node belonging to another logical network, comprising the
steps of: receiving a packet containing a destination node
information transmitted through a first virtual connection
available for transmitting the packet from the first node;
analyzing the destination node information contained in the packet
at a network layer level, and determining a second virtual
connection available for transmitting the packet to the second
node; transmitting the packet through the second virtual
connection, while storing a correspondence relationship between the
first virtual connection used in receiving the packet and the
second virtual connection used in transmitting the packet in a
memory; and transferring a newly received packet without carrying
out a network layer level analysis according to the correspondence
relationship when the correspondence relationship for a virtual
connection used in receiving the newly received packet is stored in
the memory.
[0035] This aspect of the present invention defines a method for
forming a bypass pipe without using a control message according to
the present invention.
[0036] Thus, in a case of forming a bypass pipe by using a control
message, there is provided a network system, comprising: a
plurality of virtual connection-oriented logical networks; a
plurality of network nodes connected to the logical networks, the
nodes include terminal nodes and network interconnection
apparatuses interconnecting the logical networks, each network
interconnection apparatus has a memory means for storing a
correspondence relationship between a virtual connection available
for transmitting a packet from one network node and a virtual
connection available for transmitting the packet to another network
node, and each network interconnection apparatus transfers a newly
received packet without carrying out a network layer level analysis
when a correspondence relationship for a virtual connection used in
receiving the newly received packet is stored in the memory means,
whereas each network interconnection apparatus transfers the newly
received packet by carrying out the network layer level analysis
when the correspondence relationship for a virtual connection used
in receiving the newly received packet is not stored in the memory
means; wherein each network node belonging to one logical network
and wishing to transfer the packet to another network node
belonging to another logical network transmits a control message
containing an identification information for a desired virtual
connection available for transmitting the packet without a network
layer level processing over different logical networks, according
to which each network interconnection apparatus connected between
said one logical network and said another logical network updates
the connection relationship stored in the memory means.
[0037] On the other hand, in a case of forming a bypass pipe
without using a control message, there is provided a network
system, comprising: a plurality of virtual connection-oriented
logical networks; a plurality of network nodes connected to the
logical networks, the network nodes include terminal nodes and
network interconnection apparatuses interconnecting the logical
networks, each network interconnection apparatus has a memory means
for storing a correspondence relationship between a first virtual
connection available for transmitting a packet from one network
node and a second virtual connection available for transmitting the
packet to another network node, and each network interconnection
apparatus transfers a newly received packet without carrying out a
network layer level analysis when a correspondence relationship for
a virtual connection used in receiving the newly received packet is
stored in the memory means, whereas each network interconnection
apparatus transfers the newly received packet by carrying out the
network layer level analysis when the correspondence relationship
for a virtual connection used in receiving the newly received
packet is not stored in the memory means; wherein when each network
interconnection apparatus receives the newly received packet
transmitted through the first virtual connection, each network
interconnection apparatus analyzes a destination node information
contained in the newly received packet at a network layer level and
determine the second virtual connection to update the connection
relationship stored in the memory means.
[0038] It is to be noted that the virtual connection-oriented
network here refers to a network capable of setting a plurality of
virtual connections between a terminal apparatus and a network
interconnection apparatus (router) or between network
interconnection apparatuses (routers), and changing a purpose of
using each of these virtual connections, connection by connection.
ATM, frame relay, and X.25 are examples of the virtual
connection-oriented network.
[0039] Also, a logical network here refers to a network that can be
handled logically as a single entity, regardless of a physical
configuration. For example, a logical network is defined by a range
sharing an identical network ID in a certain physical network
configuration.
[0040] On the other hand, a packet here refers to a packet of a
network layer as well as a packet of a datalink layer such as an
ATM cell, an Ethernet frame, an AAL PDU (ATM Adaptation Layer
Protocol Data Unit), etc.
[0041] Other features and advantages of the present invention will
become apparent from the following description taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] FIG. 1 is a schematic block diagram showing an overall
configuration of one embodiment of an ATM network according to the
present invention.
[0043] FIG. 2 is a schematic block diagram showing an internal
configuration of each ATM-LAN in the ATM network of FIG. 1.
[0044] FIG. 3 is a diagrammatic illustration of a routing table
provided in each ATM switch node in the ATM-LAN of FIG. 2.
[0045] FIG. 4 is a block diagram showing a configuration of each
router in the ATM network of FIG. 1.
[0046] FIG. 5 is a block diagram showing a configuration of a 2
port router that can be used as each router in the ATM network of
FIG. 1.
[0047] FIG. 6 is a block diagram showing a physical internal
configuration of a general purpose computer implementing the 2 port
router of FIG. 5.
[0048] FIG. 7 is a flow chart showing a procedure for packet
transfer by the router of FIG. 4.
[0049] FIG. 8 is a diagrammatic illustration of an L3 routing table
that can be provided-in the router of FIG. 4.
[0050] FIG. 9 is a block diagram showing a configuration of each
transmission terminal in the ATM network of FIG. 1.
[0051] FIG. 10 is a diagrammatic illustration of a VC management
table content used in the transmission terminal of FIG. 9.
[0052] FIG. 11 is a diagrammatic illustration of a destination
management table content used in the transmission terminal of FIG.
9.
[0053] FIG. 12 is a flow chart showing a procedure for transmitting
a data packet by the transmission terminal of FIG. 9.
[0054] FIG. 13 is a diagram showing possible outlines of a
procedure for set up/release of a bypass pipe using a hard state
scheme in the ATM network of FIG. 1.
[0055] FIG. 14 is a diagram showing a detailed control message
sequence to be used at a time of bypass pipe set up in one
case.
[0056] FIG. 15 is a diagram showing a detailed control message
sequence to be used at a time of bypass pipe set up in another
case.
[0057] FIG. 16 is a diagram showing a detailed control message
sequence to be used at a time of bypass pipe set up in still
another case.
[0058] FIG. 17 is a table summarizing operations of the router in
the control message sequences of FIGS. 14 to 16 and FIGS. 19 to
21.
[0059] FIGS. 18A, 18B, 18C, 18D, and 18E are diagrammatic
illustrations of a VC management table, an available VC table, a
bypass pipe management table, an IP-VC correspondence table, and an
IP routing table, respectively, which are used by the operations of
the router summarized in FIG. 17.
[0060] FIG. 19 is a diagram showing a detailed control message
sequence to be used at a time of bypass pipe release in one
case.
[0061] FIG. 20 is a diagram showing a detailed control message
sequence to be used at a time of bypass pipe release in another
case.
[0062] FIG. 21 is a diagram showing a detailed control message
sequence to be used at a time of bypass pipe release in still
another case.
[0063] FIG. 22 is a state transition diagram summarizing procedures
and internal operations for bypass pipe set up and release using a
hard state scheme in the ATM network of FIG. 1.
[0064] FIG. 23 is a flow chart showing an operation of one router
in an exemplary bypass pipe set up procedure using control message
exchanges.
[0065] FIG. 24 is a flow chart showing an operation of another
router in an exemplary bypass pipe set up procedure using control
message exchanges.
[0066] FIG. 25 is a schematic block diagram showing an exemplary
situation used in explaining an exemplary bypass pipe set up
procedure using control message exchanges.
[0067] FIG. 26 is a diagram showing possible outlines of a
procedure for set up/release of a bypass pipe using a soft state
scheme in the ATM network of FIG. 1.
[0068] FIG. 27 is a state transition diagram summarizing procedures
and internal operations for bypass pipe set up and release using a
receiver initiative soft state scheme in the ATM network of FIG.
1.
[0069] FIG. 28 is a table summarizing operations of the router in
the procedure for set up/release of a bypass pipe using a receiver
initiative soft state scheme.
[0070] FIG. 29 is a state transition diagram summarizing procedures
and internal operations for bypass pipe set up and release using a
sender initiative soft state scheme in the ATM network of FIG.
1.
[0071] FIG. 30 is a table summarizing operations of the router in
the procedure for set up/release of a bypass pipe using a sender
initiative soft state scheme.
[0072] FIG. 31 is a flow chart showing an operation of a router in
the ATM network of FIG. 1 in a case of a change in the routing
table due to the routing protocol operation.
[0073] FIG. 32 is a diagram showing an outline of a procedure for
setting up a bypass pipe using a in-band scheme in the ATM network
of FIG. 1.
[0074] FIG. 33 is a flow chart showing an operation of one router
in one method for a bypass pipe set up in a case of using SVC.
[0075] FIG. 34 is a flow chart showing an operation of another
router in one method for a bypass pipe set up in a case of using
SVC.
[0076] FIG. 35 is a diagram showing possible control message
sequences in another method for a bypass pipe set up/release in a
case of using SVC.
[0077] FIG. 36 is a schematic block diagram showing an exemplary
configuration for the ATM network of FIG. 1.
[0078] FIG. 37 is a flow chart showing an operation at a time of
starting the bypass pipe set up procedure in a case of using a
statistical information.
[0079] FIG. 38 is a flow chart showing an operation at a time of
starting the bypass pipe set up procedure in a case of using a
router activation timing.
[0080] FIG. 39 is a flow chart showing an operation at a time of
starting the bypass pipe set up procedure in a case of using a
packet transmission timing.
[0081] FIG. 40 is a flow chart showing an operation of one router
in one bypass pipe set up procedure using no control message.
[0082] FIG. 41 is a flow chart showing an operation of another
router in one bypass pipe set up procedure using no control
message.
[0083] FIG. 42 is a schematic block diagram showing another
exemplary configuration for the ATM network of FIG. 1 for
explaining another bypass pipe set up/release procedure using no
control message.
[0084] FIG. 43 is a block diagram showing a configuration of each
terminal in the exemplary configuration of FIG. 42.
[0085] FIG. 44 is a block diagram showing a configuration of each
router in the exemplary configuration of FIG. 42.
[0086] FIGS. 45A, 45B, 45C, 45D, and 45E are diagrammatic
illustrations of router control tables provided in switches in the
exemplary configuration of FIG. 42.
[0087] FIGS. 46A, 46B, 46C, and 46D are diagrammatic illustrations
of VC management tables provided in a host H1, a host H2, a router
A, and router B, respectively, in the exemplary configuration of
FIG. 42.
[0088] FIG. 47 is a flow chart showing a procedure for data packet
transmission by a transmission terminal in the exemplary
configuration of FIG. 42.
[0089] FIG. 48 is a flow chart showing a procedure for data packet
handling by a router in the exemplary configuration of FIG. 42.
[0090] FIG. 49 is a diagrammatic illustration of a VC management
table content for still another bypass pipe set up/release
procedure using no control message.
[0091] FIG. 50 is a flow chart showing a procedure for data packet
transmission by a transmission terminal in a procedure using the VC
management table content of FIG. 49.
[0092] FIG. 51 is a flow chart showing a procedure for data packet
handling by a router in a procedure using the VC management table
content of FIG. 49.
[0093] FIG. 52 is a schematic block diagram showing still another
exemplary configuration for the ATM network of FIG. 1 for
explaining a bypass pipe set up procedure for a multi-point to
point connection.
[0094] FIG. 53 is a flow chart showing an operation of one router
in a bypass pipe set up procedure for a multi-point to point
connection.
[0095] FIG. 54 is a schematic block diagram showing exemplary
connections among some routers in the still another exemplary
configuration of FIG. 52.
[0096] FIG. 55 is a schematic block diagram showing an exemplary
multi-point to point connection among some routers in the still
another exemplary configuration of FIG. 52.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0097] Now, the preferred embodiment in a form of an ATM network
incorporating the network interconnection apparatus, the network
node apparatus, and the packet transfer method according to the
present invention will be described in detail.
Configuration of ATM-LAN
[0098] The ATM network of this embodiment has an overall
configuration of an ATM internet as shown in FIG. 1, which
comprises ATM-LANs 603 and Ethernets 600 interconnected by routers
601, and Hosts 602 connected to the ATM-LANs 603 or the Ethernets
600.
[0099] Here, the ATM-LAN 603 is a local area network operated by
the ATM scheme, and this ATM-LAN 603 may very well be operated
according to the protocol defined by the standardizing organization
such as the ATM forum for example. The router 601 is a device for
mutually connecting a plurality of LANs (ATM-LANs in this
embodiment). The Host 602 is a device for carrying out transmission
and reception of packets.
[0100] In this ATM internet configuration of FIG. 1, the ATM-LAN
603 functions as a sub-net of the IP (Internet Protocol) so that
each ATM-LAN 603 has a sub-net address (sub-net ID). In the
following, only an exemplary case of using IP/IP address as network
layer protocol/network layer address constituting the ATM internet
will be described, but the similar description is also possible for
the other protocols such as netware/IPX, AppleTalk, etc. Also, in
the following description, a term "sub-net" is intended to imply
"logical network in the network layer".
[0101] It should be apparent from the foregoing description that
this embodiment concerns with a case in which the physical LAN
(ATM-LAN) and the logical sub-net (IP sub-net) coincide with each
other, that is, a case in which each ATM-LAN corresponds to one
sub-net. Here, however, the similar description is also possible
for a case in which a plurality of sub-nets are logically
constructed within one ATM-LAN, assuming that the router provides
support (of the network management, the datagram transmission,
etc.) for these plurality of sub-nets as well.
[0102] Next, an exemplary internal configuration of the ATM-LAN 603
is shown in FIG. 2, which comprises mutually connected ATM switch
nodes 21 to 24 and terminal devices 2A to 2G connected to the ATM
switch nodes 21 to 24.
[0103] Each of the ATM switch nodes 21 to 24 is a switching hub
which contains a built-in ATM switch (or device having an
equivalent function as an ATM switch) therein, and which has a
plurality of ports through which it is connected with the terminal
devices or the other ATM switch nodes. In this embodiment, it is
assumed that the connection interface among them is in the ATM
scheme. Each of these nodes has a routing table in a form shown in
FIG. 3 in which an interface and a corresponding VPI/VCI are
specified for the input side and the output side such that the data
transfer can be carried out according to this table.
[0104] Each of the terminal devices 2A to 2G is a device such as a
personal computer (PC), a workstation (WS), a printer, a server,
etc., which has an ATM interface (or a terminal adaptor having an
ATM interface) for direct connection with the ATM-LAN.
[0105] Each ATM-LAN 603 in FIG. 1 has this type of an internal
configuration formed by the ATM switch nodes and the terminal
devices, but the factors such as a topology among the internal ATM
switch nodes, a connection interface speed, a number of nodes, a
number of terminals, etc. are arbitrary in each ATM-LAN.
[0106] This ATM-LEN 603, which is an LAN in accordance with the ATM
forum for example, has the following features.
[0107] (1) Each terminal device or ATM switch node has a its own
link layer address (ATM address in this embodiment). Here the link
layer addresses do not overlap with each other within one
ATM-LAN.
[0108] (2) Each terminal device or ATM switch node has its own IP
address as the network layer address, where the network layer
address is a globally unique address in general.
[0109] (3) Each terminal device or ATM switch node has a broadcast
channel with respect to the ATM-LAN to which it belongs, such that
each terminal device or ATM switch node can transmit a message
(cell) simultaneously to all the other terminals/nodes belonging to
that ATM-LAN through the broadcast channel.
[0110] Each ATM-LAN also has a VPI/VCI value determination function
(not shown) provided therein which has a right to determine the
VPI/VCI values to be used within each ATM-LAN, which is an
independent right in each ATM-LAN. Whenever there is a data to be
transmitted, the terminal device or node in the ATM-LAN loads that
data into an ATM cell, attaches a prescribed ATM cell header, and
transmits that ATM cell in that ATM-LAN, regardless of whether the
transmission destination is within that ATM-LAN.
[0111] Now, some terms to be used in this embodiment will be
defined.
[0112] A network layer level indicates a basic unit of transfer
through the network, which is a layer for handling the routing
control, etc. An address to be used in the transfer or the routing
control at the network layer will be referred as a network layer
address.
[0113] A host is a device other than the router which transmits and
receives packets of the network layer level, such as a terminal
device for instance.
[0114] A node is a generic name indicating the router and the
host.
[0115] Neighboring routers are routers that can directly transmit
the packets of the network layer level with one another, without
being intermediated by the other routers.
[0116] A VCID (VC IDentifier) is an identifier for identifying a
virtual connection (VC), which is identical between the host and
the router, as well as between the neighboring routers. In a case
of the ATM, a correspondence relationship between the VCID and
VPI/VCI is stored at each host and router. The VCID is unique
within a range in which the VC is set up (which is within the ATM
network in this embodiment).
[0117] A dedicated VC is a VC to be set up between the host and the
router or between the neighboring routers, which is used at a time
of forming a bypass pipe.
[0118] A default VC is a VC to be set up between the host and the
router or between the neighboring routers, which is used at a time
of transferring the packet hop by hop.
[0119] A bypass pipe is a connection formed by connecting a
plurality of dedicated VCs, which provides a mechanism for sending
the data packet from a transmitting terminal to a receiving
terminal by using only a lower level packet transfer unit, without
passing through a packet transfer unit of the network layer level,
at a network interconnection apparatus through which the data
packet passes in its course.
Configuration of Router
[0120] In this embodiment, each router has a configuration as shown
in FIG. 4, which comprises: a plurality of network interface units
(network I/F units) 201; a datalink layer switch unit 202 connected
with the network I/F units 201; a datalink layer-network layer
translation unit 203 connected with the datalink layer switch unit
202; a network layer switch unit 204 connected with the datalink
layer-network layer translation unit 203; a data link layer
connection set up judgement unit 205 connected with the network
layer switch unit 205; a datalink layer control unit 206 connected
with the datalink layer switch unit 202, the network layer switch
unit 204, and the datalink layer connection set up judgement unit
205; and a network layer control unit 207 connected with the
network layer switch unit 204.
[0121] This router of FIG. 4 is connected with a desired LAN such
as the ATM-LAN, Ethernet, FDDI, etc., through each network I/F unit
201, and at least one of the plurality of network I/F units 201 is
accommodating a virtual connection-oriented LAN such as the
ATM-LAN. Here, the LANs such as the ATM-LAN, Ethernet, etc. are
treated as the datalink layer.
[0122] In the following, the datalink layer is also referred as L2,
while the network layer is also referred as L3.
[0123] The datalink layer switch unit 202 is a unit for determining
an output network I/F unit 201 for a datalink layer frame according
to a header address of a datalink layer frame whenever a datalink
layer frame arrives from the LAN connected with the network I/F
unit 201 or from the datalink layer-network layer translation unit
203. In order to determine the output network I/F unit 201, this
datalink layer switch unit 201 is provided with a datalink layer
routing table (L2 routing table) therein, where this datalink layer
routing table is managed by the datalink layer control unit 206. By
providing this datalink layer switch unit 202, it becomes possible
to carry out a faster packet/cell switching compared with a case of
using only a network layer switching.
[0124] The datalink layer-network layer translation unit 203
carries out a translation from an L2 frame to an L3 packet, and
from an L3 packet to an L2 frame. This corresponds to an AAL in the
ATM for instance. Thus, in a case an ATM cell is entered from the
datalink layer switch unit 202, the entered ATM cell is assembled
into an L3 packet. Also, in a case an L3 packet is entered from the
network layer switch unit 204, the entered L3 packet is
disassembled into an ATM cell.
[0125] The network layer switch unit 204 has an L3 routing table
and a function similar to those of a conventional router, in which
a destination address of an L3 packet is checked and compared with
the L3 routing table to determine an output network I/F.
[0126] The datalink layer connection set up judgement unit 205
judges the switching from a network layer transfer in which an
output target is determined by the network layer switch unit 204 to
a datalink layer transfer in which an output target is determined
by the datalink layer switch unit 202, when packets over a
prescribed number have been entered, outputted, or passed according
to an input/output statistics data for L3 packets, or when there is
a notice from an upper protocol. By means of this function, it is
possible to realize a high speed packet transfer. Here, the
datalink connection can be newly set up by the datalink layer
control unit 206 at a time of switching from the network layer
transfer to the datalink layer transfer, or the datalink
connections may be set up in advance and an unused datalink
connection is used at a time of switching from the network layer
transfer to the datalink layer transfer. A method for judging the
switching in this datalink layer connection set up judgement unit
205 will be described in detail later.
[0127] The datalink layer control unit 206 carries out a set
up/release of a connection, and a relaying of packets for the sake
of connection set up/release, in a case the datalink layer is a
connection oriented one such as the ATM. Here, a connection
information for connections set up or released by this datalink
layer control unit 206 is registered or deleted in the L2 routing
table provided in the datalink layer switch unit 202.
[0128] The network layer control unit 207 has a function for
managing the L3 routing table provided in the network layer switch
unit 204. In a case the L3 routing table is static, the L3 routing
table is set up only once at the beginning. In a case of a dynamic
routing, the routing information is exchanged with neighboring
routers in order to manage the L3 routing table. The routing
information exchange among the neighboring routers can be realized
by using the existing routing protocol such as RIP (Routing
Information Protocol), OSPF (Open Shortest Path First), etc.
[0129] Next, the router having physical interfaces with respect to
two ATM-LANs will be described as an exemplary case of the router
of this embodiment. This type of router will be referred as a "2
port router".
[0130] The 2 port router has a configuration as shown in FIG. 5,
which logically comprises: network I/Fs (network interface-A and
network interface-B) 31 and 33; an add/drop and header conversion
unit 32 provided between the network I/Fs 31 and 33; an AAL
processing unit 34 connected with the add/drop and header
conversion unit 32; and a network layer processing unit 35, a
datalink layer control unit 36, and a router control unit 37, all
of which are connected with the AAL processing unit 34.
[0131] The network I/Fs 31 and 33 are provided in correspondence to
the physical ports of the router, to function as the physical
interfaces with respect to the ATM-LANs. Each network I/F has
functions for carrying out a conversion processing between a signal
on a physical transmission medium and an ATM cell, such as E/O
conversion, O/E conversion, SDH (Synchronous Digital Hierarchy)
processing, cell synchronization processing, scrambling/descrabling
processing, etc. for example, as well as an exchange of ATM cells
with respect to the add/drop and header conversion unit 32.
[0132] The add/drop and header conversion unit 32 corresponds to
the datalink layer switch unit 202 of FIG. 4, and has a function
for dropping (extracting) cells having prescribed ATM cell header
values (such as VPI/VCI/PT values) among the cells transmitted from
the network I/Fs 31 and 33 and sending out the dropped cells to the
AAL processing unit 34, a function for converting cell headers of
cells having prescribed ATM cell header values according to a
header conversion table provided therein and sending out these
cells to a network I/F on an opposite side (without sending them to
the AAL processing unit 34), and a function for adding (inserting)
and sending out the ATM cells handed from the AAL processing unit
34 into a specified direction. In this add/drop and header
conversion unit 32, in a case cells having ATM cell header values
which are not registered in the header conversion table are
entered, these cells may be discarded in this module and empty
cells may be inserted and outputted to an output side instead.
[0133] The AAL processing unit 34 corresponds to the datalink
layer-network layer translation unit 203 of FIG. 4, and has a
function for cell disassembling the ATM cells handed from the
add/drop and header conversion unit 32, assembling the upper layer
packets (such as IP packets), and handing the packets to a
processing unit of a destination upper layer (such as a router
processing unit or a router control unit in this embodiment), and a
function for cell assembling the packets handed from a processing
unit of an upper layer (such as a router processing unit) and
sending out to the add/drop and header conversion unit 32.
[0134] The network layer processing unit 35 corresponds to the
network layer switch unit 204 and the network layer control unit
207 of FIG. 4, and has a function of the router for carrying out
the network layer processing (that is, a function for receiving
datagram (such as IP datagram) from the AAL processing unit 34 and
carrying out the routing processing for this datagram, while
carrying out data exchange or data processing for the routing
protocol (such as RIP or OSPF) with respect to the other routers),
and a function for carrying out data exchange and data processing
for "AT1 internet bypass pipe set up protocol" to be described
later, as well as processing necessitated by the processing result
of this protocol by acting on the datalink layer control unit 36
and the add/drop and header conversion unit 32.
[0135] The datalink layer control unit 36 has a function for
carrying out a connection processing for the datalink layer
(ATM-LANs in this embodiment) connected through the network I/Fs 31
and 33, as well as a signaling processing and call processing.
[0136] The router control unit 37 has a function for carrying out a
control of the router as a whole, and carries out an initialization
of the router as well.
[0137] Now, the router of this embodiment can be constructed by
using a dedicated device, or by using a general purpose computer
such as a personal computer or a workstation. Here, a case of
constructing the 2 port router described above by using a general
purpose computer (a workstation in this embodiment) will be
described.
[0138] In this case, the 2 port router has a physical internal
configuration as shown in FIG. 6, which generally comprises a
workstation (WS) 41 and a communication board 42 connected to the
WS 41 as an extension board. Here, the WS 41 has no communication
interface in a form of the ATM interface, and the ATM interface
function is provided by the communication board 42.
[0139] The communication board (ATM communication board) 42
comprises: a physical interface handling unit-A 421 connected with
one physical transmission medium through one ATM communication
interface; a cell synchronization unit-A 422 connected with the
physical interface handling unit-A 421; a physical interface
handling unit-B 423 connected with another physical transmission
medium through another ATM communication interface; a cell
synchronization unit-B 424 connected with the physical interface
handling unit-B 423; an add/drop and header conversion unit 425
connected with the cell synchronization unit 422 and the cell
synchronization unit 424; an AAL processing unit 426 connected with
the add/drop and header conversion unit 425; and a bus interface
unit 427 connected with the AAL processing unit 426 and a standard
bus I/F for interfacing the WS 41 and the communication board
42.
[0140] The WS 41 comprises: a CPU 411, a main memory 412, a hard
disk (HD) 414, and a bus interface (bus I/F) 413 connected with the
CPU 411 and the main memory 412 through a main bus 415 as well as
with the HD 414 and the standard bus I/F through a peripheral bus
416. Here, the other usual elements of the WS 41 such as CRT, frame
memory, other network interfaces, etc. are omitted in FIG. 6.
[0141] Each element of the communication board 42 has the following
functions.
[0142] Each of the physical interface handling units 421 and 423
has a function for carrying out a conversion between the physical
transmission medium (such as optical fiber, coaxial cable,
shield-less twist pair cable, etc.) and a physical processing
scheme within the communication board 42 (electric interface in
this embodiment). In addition, each physical interface handling
unit also has a function for adapting the transmission scheme to
the SDH scheme when the physical transmission medium uses such an
ATM cell transmission scheme, a function for notifying an
abnormality of the physical interface handling unit to the
external, and registers for initial settings, etc.
[0143] Each of the cell synchronization units 422 and 424 has a
function for taking a synchronization in ATM cell unit by referring
to and processing an HEC (Header Error Control) field of an ATM
cell in the bit stream entered from the physical interface handling
unit 421 or 423, and a function for calculating and inserting the
HEC field into an ATM cell transmitted from the add/drop and header
conversion unit 425.
[0144] In the following, an interface formed by the physical
interface handling unit-A 421 and the cell synchronization unit-A
422 will be referred as an A-side interface, while an interface
formed by the physical interface handling unit-B 422 and the cell
synchronization unit-B 424 will be referred as a B-side interface.
These A-side interface and B-side interface correspond to the
network interface-A 31 and the network interface-B 33 of FIG. 5,
respectively.
[0145] The add/drop and header conversion unit 425 has a function
for dropping (extracting) cells having prescribed ATM cell header
values (such as VPI/VCI/PT values) among the cells transmitted from
the cell synchronization units 422 and 424 and sending out the
dropped cells to the AAL processing unit 426, a function for
converting cell headers of cells having prescribed ATM cell header
values according to a header conversion table provided therein and
sending out these cells to the cell synchronization unit on an
opposite side, and a function for adding (inserting) and sending
out the ATM cells handed from the AAL processing unit 426 into a
specified direction (a cell synchronization unit in a specified
direction). In this add/drop and header conversion unit 425, in a
case cells having ATM cell header values which are not registered
in the header conversion table are entered, these cells are
discarded in this module and empty cells are inserted and outputted
to an output side instead.
[0146] The AAL processing unit 426 has a function for cell
disassembling the ATM cells handed from the add/drop and header
conversion unit 425, assembling them in forms of the upper layer
packets, storing these packets, and handing these packets to the
bus interface 427 according to the need, and a function for storing
the upper layer packets handed from the bus interface 427, ATM cell
assembling these packets according to the need, sending out these
ATM cells to the add/drop and header conversion unit 425.
[0147] The bus interface 427 has a function for interfacing the
input/output data of the standard bus interface of the WS 41 with
respect to the communication board 42, and a function for relaying
the set up commands to each module within the communication board
42 from the WS 41 side given through the standard bus interface or
the notices from each module within the communication board 42 to
the WS 41 side, so as to carry out the control of each module in
the communication board 42.
[0148] Next, each element of the WS 41 has the following
functions.
[0149] The CPU 411 is a main processor of the WS 41, where an
operating system operable on the WS 41 and various application
programs operable on the WS 41 are operated on this CPU 411. In
addition, in this embodiment, the configuration of FIG. 6 operates
as the router, so that the software of the application programs for
the router are also operated on this CPU 411.
[0150] Here, the application programs for the router includes:
[0151] (1) a control/management program for the router,
[0152] (2) a link layer connection control program for setting up,
changing, disconnecting, and managing link layer connection (ATM
connection) between the router and the link layer network (ATM-LAN)
connected to it,
[0153] (3 ) a network layer processing (router processing) program,
and
[0154] (4) a control program of the communication board 42.
[0155] It is to be noted that the link layer connection (2) and a
part of the control program of the communication board 42 (4) may
be implemented as a device driver of the WS 41 by regarding the
communication board 42 as one of the devices for the WS 41.
[0156] The main memory 412 is a main data storage device for the WS
41.
[0157] The bus interface 413 has a function for electrically
connecting/disconnecting the main bus 415 and the peripheral bus
416 according to commands from the CPU 411.
[0158] The hard disk (HD) 414 is a large capacity data memory
device connected to the peripheral bus 416.
[0159] The WS 41 has at least one extension slot, and this
extension slot has its own peripheral bus 416 and a corresponding
bus (such as S bus, TURBO bus, ISA bus, PCI bus, etc.).
[0160] Also, it may be possible for the WS 41 of this embodiment to
have a configuration capable of directly referring to addresses of
a memory provided in the bus interface unit 427 or in the AAL
processing unit 426 through the bus interface unit 427 in the
communication board 42, via the standard bus interface. Namely, it
may be possible for the CPU 411 to regard a memory space within the
communication board 42 as a part of the address space (or I/O
space) directly visible from the CPU 411.
[0161] The bus interface unit 427 in the communication board 42
connected with the WS 41 has a function for carrying out a control
of each module within the communication board 42 as described
according to commands from the CPU 411. In other words, the CPU 411
carries out various settings of each module in the communication
board 42 via the bus interface unit 427, according to commands from
the router software operated on the CPU 411 described above, as
follows.
[0162] First, the router software operated on the CPU 411 carries
out the initialization of the communication board 42. This
initialization includes the link layer connection processing
software, the network management software, and the router
processing software as the inter-networking device softwares
operated on the CPU 411, a function of connection set up in the
ATM-LAN connected to the router, and an establishment of the ATM
connection/upper layer connection with respect to the other
routers, etc. The establishment of the ATM connection is realized
as the router software operated on the CPU 411 sets up the specific
processing contents with respect to the add/drop and header
conversion unit 425 via the bus interface unit 427, such as "those
ATM cells which have prescribed ATM cell header values among the
ATM cells entered from a certain physical interface are to be
dropped to the WS 41 side", "the AAL processing unit 426 is to cell
disassemble the dropped ATM cells and hand them to the CPU 411 (or
the router software provided therein) through the bus interface
unit 427", and "in order to output data from the CPU 411 (or the
router software provided therein) to the external of the WS 41,
that data is to be handed to the AAL processing unit 426 through
the bus interface unit 427, and ATM cell assembled by attaching the
prescribed ATM cell header value there, and then the ATM cell is to
be added and outputted to an appropriate physical interface side by
the add/drop and header conversion 425".
[0163] At this point, the data exchange between the WS 41 and the
communication board 42 may be realized by using a scheme for
specifying one of the A-side and B-side physical interfaces from
which that data was transmitted or to which that data is to be
transmitted, along with the ATM cell header value.
[0164] Next, an ATM connection which passes through the router at
the ATM layer processing alone (which will be referred hereafter as
a bypass ATM connection) will be described.
[0165] A set up of a bypass ATM connection to be set over the
router is carried out by various programs operated on the CPU 411.
A physical setting of the actual bypass ATM connection is made as
follows. Namely, the software operated on the CPU 411 sets up the
processing content that "an ATM cell entered from the physical
interface of one side (A-side for instance) which has a specific
ATM cell header value (header value=X for instance) is to be
outputted to another side (B-side for instance) after the cell
header value is rewritten into a prescribed value (header value=Y
for instance)", with respect to the add/drop and header conversion
unit 425 through the bus interface unit 427. An appropriate setting
is also made with respect to the add/drop and header conversion
unit 425 in a case there is an ATM connection in opposite direction
(such as a ATM connection in B.fwdarw.A direction, or a
bidirectional connection). By means of this, the ATM cell with the
header value=X entered from the A-side for example will be
outputted to the B-side interface with the cell header value
rewritten into the header value=Y. At this point, in the router
(i.e., in the communication board), only the ATM layer processing
is carried out. In this manner, it is possible to set up a bypass
ATM connection which passes through the communication board 42 at
the ATM layer processing alone.
[0166] Here, the add/drop and header conversion unit 425 may be
provided with a UPC function, i.e., a policing/shaping function
therein. Namely, it is possible to carry out a cell flow monitoring
or a cell flow regulation on the cell flow having specific ATM cell
header values.
Procedure for Packet Transfer
[0167] Next, a procedure for packet transfer by the router in this
embodiment as shown in FIG. 4 will be described with reference to
the flow chart of FIG. 7.
[0168] When the datalink layer frame is entered from the network
I/F unit 201 (step S1), the datalink layer switch unit 202 searches
through the L2 routing table t1 with an input connection ID or L2
destination address of the received datalink layer frame as a
search key (step S2) to determine the output I/F.
[0169] In a case the search is successful, the received datalink
layer frame is handed to the output I/F registered in the searched
out entry, while the output connection ID in the packet is
rewritten according to the searched out entry of the L2 routing
table (step S6), and the received datalink layer frame is outputted
from the network I/F unit 201 of the determined output I/F (step
S13).
[0170] On the other hand, when the determined output I/F indicates
an upper layer, or when there is no corresponding entry, the
received datalink layer frame is handed to the datalink
layer-network layer translation unit 203 to carry out an assembling
of L3 packet from L2 frame (step S3). For example, in a case of the
ATM, the AAL processing is to be carried out here, whereas in a
case of the Ethernet, the header is to be removed here. After the
translation from the L2 frame to the L3 packet is carried out, the
network layer switch unit 204 determines whether this L3 packet is
destined to this node or not (step S4), and if so, the L3 packet
destined to this node is handed to the upper layer (the network
layer control unit 207, the datalink layer control unit 206, the
datalink layer connection set up judgement unit 205) (step S5).
Otherwise, the L3 packet is not destined to this node and to be
transferred, so that the following operation is carried out for a
transmission of a packet.
[0171] Namely, the network layer switch unit 204 searches through
the L3 routing table t4 with a destination L3 address of the packet
as a search key, to determine the next hop L3 address and the
output I/F (step S8). Here, the destination L3 address may not
necessarily be the destination address to which the packet is to be
transferred, and can be any of a source address, a network mask, a
flow ID to be set by IPng, an application ID such as a TCP/UDP
port, etc. By using the network mask, it becomes possible to
specify a group of a plurality of hosts rather than specifying just
one destination host, so as to enable more general destination
specification. Also, by using the flow ID or the TCP/UDP port, it
becomes possible to specify a specific application of the
destination host, SO as to enable more detailed destination
specification. In the following, it is assumed that the destination
address is indicated by any one or more of "address of destined
host", "network mask of destined host", "address of source host",
"network mask of source host", "flow ID", and "transport layer port
(such as TCP/UDP port)".
[0172] When the output I/F is determined by the L3 routing table
search, a dedicated VC table t3 is searched by the datalink
layer-network layer translation unit 203 to check if there is an
entry for the destination address in this dedicated VC table t3
(step S9). This dedicated VC table t3 is managed by the datalink
layer control unit 206 and an entry is registered in this dedicated
VC table t3 when L2 forward is made without making L3 forward at a
router in a middle. By searching through this dedicated VC table
t3, it is possible to determine the connection ID to be attached to
the packet to be outputted from the destination L3 address.
Consequently, by using this dedicated VC table t3, it becomes
possible to carry out the L2 transfer by routers at a next and
farther stages, so as to realize a high speed packet transfer. When
a corresponding entry is found by the dedicated VC table search,
the operation proceeds to the step S12 described below.
[0173] When no corresponding entry is found by the dedicated VC
table search, a default VC table t2 is searched by the datalink
layer-network layer translation unit 203 (step S10). This default
VC table t2 registers the routers/terminals existing in the same
LAN, for a use in a case of the L3 packet transfer to a next hop,
hop by hop. When a corresponding entry is found by the default VC
table search, the operation proceeds to the step S12 described
below.
[0174] When no corresponding entry is found by the default VC table
search either, the output connection ID remains unknown, so that
the L2 address is resolved from the L3 address by using ARP
(Address Resolution Protocol), a connection (VC) is set up, and a
corresponding entry is registered in the default VC table t2, while
the packet is outputted by using its output connection ID, at the
datalink layer-network layer translation unit 203 (step S11).
[0175] The packet with the output connection ID determined is then
converted from L3 packet to L2 frame at the datalink layer-network
layer translation unit 203 (step S12), and outputted to the LAN
through the network I/F unit 201 of the determined output I/F (step
S13).
[0176] Also, when there is an entry from the upper layer (step S7),
the steps S8 to S13 described above is carried out similarly for
the transmission of a packet.
[0177] In the above described procedure, the dedicated VC table and
the default VC table are provided separately, but it is also
possible to combine them to form a single table. It is further
possible to form a single table by combining the L3 routing table,
the default VC table, and the dedicated VC table, if desired. In
this case, the L3 routing table has a format as shown in FIG. 8,
which differs from the L3 routing table t4 shown in FIG. 7 in that
the output connection ID (VPI/VCI) is registered in a field for the
output I/F as well, so that it suffices to search through this
table alone in determining the output connection ID, and therefore
the separate default VC table and dedicated VC table are
unnecessary.
Transmission Terminal
[0178] The steps S7 to S13 in the above described flow chart of
FIG. 7 for a packet transfer procedure at a router is a packet
transmission procedure which is also applicable to a packet
transmission at a terminal as well.
[0179] Here, another example of a transmission terminal for
transmitting a packet will be described with references to FIG. 9
to FIG. 12.
[0180] The terminal (host) 602 in FIG. 1 for transmitting and
receiving packets in this embodiment can have an exemplary
configuration as shown in FIG. 9, which comprises: an ATM layer
processing unit 621; and ATM cell-IP packet conversion unit 622
connected with the ATM layer processing unit 621; an IP layer
processing unit 623 connected with the ATM cell-IP packet
conversion unit 622, and a VC management unit 624 and a destination
management unit 627 connected with the IP layer processing unit
623. Here, the IP layer processing unit 623 includes a data packet
transmission and reception unit 6231 for carrying out transmission
and reception of data packets and a control message transmission
and reception unit 6232 for carrying out transmission and reception
of control messages, and the VC management unit 624 includes a VC
control unit 625 and a VC management table 626, while the
destination management unit 627 includes a destination control unit
628 and a destination management table 629.
[0181] Here, the VC management table 626 has an exemplary table
content as shown in FIG. 10. This VC management table 626 stores a
VC connection target IP address, I/F, VPI/VCI, and status for each
VC managed by the VC management unit 624. The status indicates
whether each VC is already in use somewhere or not.
[0182] Also, the destination management table 629 has an exemplary
table content as shown in FIG. 11. This destination management
table 629 stores a correspondence between a data transmission
destination (which can be indicated by an IP address of a
destination terminal, or by a net ID of a destination network, for
example), I/F, and VPI/VCI.
[0183] Next, a procedure for transmitting a data packet in this
transmission terminal of FIG. 9 will be described with reference to
the flow chart of FIG. 12.
[0184] When data to be transmitted (IP packet) is generated (step
S161), the destination management table 629 is referred to check if
there exists an entry corresponding to the destination IP address
in the generated IP packet (S162). In a case a corresponding entry
exists at the step S162, a corresponding I/F and a corresponding
VPI/VCI are obtained from the destination management table 629
(step S163). Then, the ATM cell is assembled according to a
prescribed format (step S168) and the data packet, i.e., the
assembled ATM cell, is transmitted (step S169).
[0185] In a case a corresponding entry does not exist at the step
S162, a next hop is determined by referring to an IP routing table
provided within the IP layer processing unit 623 (step S164). Then,
whether a transfer by a bypass pipe is wished or not is judged
(step S165).
[0186] In a case the transfer by a bypass pipe is not wished, the
VC management table 626 is referred to obtain I/F and VPI/VCI
corresponding to the next hop (step S167). Then, the ATM cell is
assembled according to a prescribed format (step S168) and the data
packet, i.e., the assembled ATM cell, is transmitted (step
S169).
[0187] In a case the transfer by a bypass pipe is wished, the
bypass pipe is created by using the control message and registered
in the destination management table 629 (step S166), and then, a
corresponding I/F and a corresponding VPI/VCI are obtained from the
destination management table 629 (step S163). Then, the ATM cell is
assembled according to a prescribed format (step S168) and the data
packet, i.e., the assembled ATM cell, is transmitted (step
S169).
Bypass Pipe Set Up/Release Procedure (Hard State)
[0188] Now, a procedure for setting up or releasing a bypass pipe
using a hard state scheme in this embodiment will be D described in
detail. In a case of ATM, the bypass pipe can be provided by either
a PVC (Permanent Virtual Channel) or a VC within VP. The bypass
pipe set up/release procedure to be described below is equally
applicable to either case, so that only a case of using PVC will be
described below as an illustrative example.
[0189] In an exemplary case in which a router-A commands set
up/release of a bypass pipe from a router-A to a router-D through a
router-B, a router-C, and ATM-LANs provided between routers as
shown in a part (a) of FIG. 13, there are two possible outlines for
a control message sequence to be used at a time of set up as
indicated in parts (b) and (c) of FIG. 13, and two possible
outlines for a control message sequence to be used at a time of
release as indicated in parts (d) and (e) of FIG. 13. In setting up
or releasing the bypass pipe, it is preferable to rewrite an ATM
routing control table within one cell time in order to maintain a
transfer efficiency for data packets. In view of this fact, a case
of using the control message sequences as outlined in a part (b)
(set up-1) and a part (e) (release-2) of FIG. 13 will be described
in detail first.
[0190] In this case, detailed control message sequences to be used
at a time of bypass pipe set up are shown in FIGS. 14, 15, and 16,
where FIG. 14 shows a control message sequence for a case in which
the bypass pipe has been set up to a target router, FIG. 15 shows a
control message sequence for a case in which the bypass pipe has
been set up to an intermediate router, and FIG. 16 shows a control
message sequence for a case in which the bypass pipe has not been
set up.
[0191] As indicated in each of FIGS. 14, 15, and 16, a black dot
symbol in these figures represents a router which made a bypass
pipe set up request command (router-A in this case), and a
partially black square symbol in these figures represents a
completion of an ATM transfer set up (ATM layer level set up).
Also, a solid line with an arrow in these figures represents a
control message. Here, a control message at a time of bypass pipe
set up is transferred to a neighboring router hop by hop, using a
default VC provided for this purpose. In addition, a rectangular
enclosure with an arrow in these figures represents a state
transition inside a router and an operation of a router at that
time, where each operation is indicated in an abbreviated format of
"AS(numeral)" whose content is specified in a table shown in FIG.
17.
[0192] In FIG. 17, each operation is specified in terms of the
following parts. A "Transmission Packet" part indicates a type of
packet to be transferred. "Bypass Pipe Management Table" parts
(output side and input side) indicate registration or deletion of a
bypass pipe management table as shown in FIG. 18C for managing from
which input port to which output port the dedicated VCs are
connected. In further detail, the bypass pipe management table of
FIG. 18C has an entry for each bypass pipe ID which specifies VCID,
VPI/VCI, and port at the input side and the output side, along with
its state (internal state). An "ATM Transfer" part indicates a set
up or release of the L2 routing table within the router to carry
out the ATM transfer. An "IP-VC Correspondence table/IP Routing
table" part indicates registration or deletion of an IP-VC
correspondence table as shown in FIG. 18D and an IP routing table
as shown in FIG. 18E. Here, the IP-VC correspondence table of FIG.
18D is used in determining which VC should the packet be outputted
at a time of transferring the packet from the first router of the
bypass pipe according to the destination IP address of the packet.
This IP-VC correspondence table of FIG. 18D is set up in the router
at an entrance of the bypass pipe when the bypass pipe is set
up.
[0193] Also, each interface is provided with a VC management table
as shown in FIG. 18A for specifying a VCID and a target IP address
for each VPI/VCI, and an available VC table as shown in FIG. 18B
for specifying a VCID for each target IP address, in addition to
the IP-VC correspondence table of FIG. 18D.
[0194] On the other hand, each node is provided with the IP routing
table of FIG. 18E for specifying a next hop IP address, an
interface, a virtual next hop IP address, and a packet count for
each destination IP address, in addition to the bypass pipe
management table of FIG. 18C. Here, the next hop IP address
indicates an address of a next node in a case of a usual hop by hop
transfer, and the virtual next hop IP address indicates an address
of a terminal point node of a bypass pipe which corresponds to a
next hop in terms of IP and which is to be used in a case of a
transfer by a bypass pipe, while the packet count indicates a
number of packets transferred, which is to be used as a statistical
information in determining a timing for the bypass pipe set up.
[0195] Now, the detailed control message sequences of FIGS. 14, 15,
and 16 will be described in further detail one by one.
[0196] FIG. 14 is a control message sequence for a case in which
the bypass pipe has been set up completely from the router-A to the
router-D. The black dot symbol indicates that the router-A receives
the bypass pipe set up request command. When this command is
received, the router-A changes the internal state for a pipe ID=#1
from an "idle" state to a "set up request transmission" state by
changing a state of the pipe ID=#1 in the bypass pipe management
table. Then, the VCID and the port used at the output side are
registered in the bypass pipe management table. In addition, the
bypass pipe set up request message is transmitted to the router-B
which is a next stage router on the way to the router-D. This
message includes the pipe ID, the VCID to be used, the final
destination address, and the sender address. In this example the
pipe ID is #1, the VCID is #2, the final destination address is the
router-D, the sender address is the router-A. Here, the final
destination address and the sender address are those contained in
the bypass pipe set up request message, and not those contained in
the header of the IP packet. These series of operations is
indicated by "AS1" in FIG. 17.
[0197] The router-B starts to operate when the bypass pipe set up
request message transmitted from the router-A is received. First,
the router-B checks the condition Pi: whether the dedicated VC to
the router-A is available and whether the router-A is permitted to
set up the bypass pipe to the router-B. Then, the router-B checks
whether the router-B itself is the last router of the bypass pipe
or not by looking up the final destination address of the received
message. Here, the condition for becoming the last router is given
by the condition P2: a case of either "a link to a next router to
which the bypass pipe set up request message is to be sent is not
ATM" or "it is in the identical sub-net as the final destination
address". For this condition P2, it is also possible to consider a
case of "a link to a next router to which the bypass pipe set up
request message is to be sent is not ATM" or "it is identical to
the final destination address".
[0198] In this example, the link to which the bypass pipe set up
request message is to be sent is ATM and the final destination
address is the router-D, so that the router-B is not the last
router of the bypass pipe. Thus, the router-B changes the internal
state for the pipe ID=#1 from an "idle" state to a "set up request
reception" state. Then, the bypass pipe set up request message is
transmitted to the router-C which is a next stage router on the way
to the router-D. Here, the content of the bypass pipe set up
request message has the same pipe ID and final destination address
as those sent by the router-A, while the VCID is changed to that
used by the router-B. After this message is transmitted, the VCIDs
and ports used here are registered in the input side and the output
side of an entry for the pipe ID=#1 in the bypass pipe management
table.
[0199] The router-C also checks whether the dedicated VC between
the router-B and the router-C is available according to the
condition P1, and whether it is the last router of the bypass pipe
according to the condition P2, just as in the router-B. In this
example, it is recognized that it is not the last router of the
bypass pipe. Thereafter, the router-C carries out the operations
similar to those of the router-B described above, and transmits the
bypass pipe set up request message to the router-D.
[0200] When the bypass pipe set up request message is received from
the router-C, the router-D checks whether the dedicated VC between
the router-C and the router-D is available according to the
condition P1, and whether it is the last router of the bypass pipe
according to the condition P2. In this example, the final
destination of this bypass pipe set up request message is the
router-D, it is recognized that it is the last router of the bypass
pipe. Then, the router-D changes the internal state from an "idle"
state to an "exit" state, and returns a bypass pipe set up response
message to the router-C from which the bypass pipe set up request
message has arrived. This message contains the pipe ID, the VCID,
and the sender address. Here, the sender address is the router-D.
Then, the VCID and port used here are registered in the input side
of the bypass pipe management table.
[0201] When the bypass pipe set up response message is received
from the router-D, the router-C changes the internal state from the
"set up request reception" state to a "relay" state. Then, a
previous stage router is recognized from the VCID registered in the
input side of the bypass pipe management table and the bypass pipe
set up response message is transmitted to the router-B. Here, the
content of this message retains the pipe ID, the final destination
address, and the sender address as received while changing the VCID
to that registered in the bypass pipe management table. Then, the
ATM routing table is changed accordingly so as to enable the ATM
transfer.
[0202] When the bypass pipe set up response message is received
from the router-C, the router-B operates similarly as the router-C,
and transmits the bypass pipe set up response message to the
router-A.
[0203] When the bypass pipe set up response message is received
from the router-B, the router-A changes the internal state from the
"set up request transmission" state to an "entrance" state, and
registers the VCID and port used here in the input side of the
bypass pipe management table. Also, the router-A changes the output
target of the IP packet from the default VC to the currently set up
bypass pipe by registering the IP address of the IP packet and the
VPI/VCI of the bypass pipe into the IP-VC correspondence table. In
addition, the virtual next hop IP address for the IP routing table
(L3 routing table) as shown in FIG. 18E is registered. By this, the
set up of the bypass pipe from the router-A to the router-D is
finished.
[0204] FIG. 15 is a control message sequence for a case in which
the bypass pipe has been set up only to an intermediate point. The
black dot symbol indicates that the router-A receives the bypass
pipe set up request command just as in a case of FIG. 14. Here, the
operations from the router-A to the router-C are the same as in a
case of FIG. 14.
[0205] When the bypass pipe set up request message is received from
the router-C, the router-D checks whether the dedicated VC is
available according to the condition P1. Then, when the condition
P1 is not satisfied, the router-D leaves the internal state in the
"idle" state, and returns the bypass pipe set up rejection message
to the router-C. This message contains the final destination
address, the sender address, the pipe ID, and the VCID. In this
example, the final destination address is the router-D, and the
sender address is the router-A.
[0206] When the bypass pipe set up rejection message is received
from the router-D, the router-C changes the internal state from the
"set up request reception" state to an "exit" state. Then, the
bypass pipe set up response message is transmitted to the router-B.
Here, the final destination address of this message is set to be
the router-C. The router-C then finishes its operation by deleting
the output side of the bypass pipe management table.
[0207] Hereafter, the router-B and the router-A operates similarly
as in a case of FIG. 14, such that eventually the bypass pipe from
the router-A to the router-C is set up.
[0208] FIG. 16 is a control message sequence for a case in which
the bypass pipe has not been set up at all as the bypass pipe set
up request transmitted from the router-A is rejected by the
neighboring router-B.
[0209] In this case, when the bypass pipe set up request message is
received, the router-B checks the condition P1 and recognizes that
there is no available dedicated VC, so that the router-B returns
the bypass pipe set up rejection.
[0210] When the bypass pipe set up rejection message from the
router-B is received, the router-A changes the internal state from
the "set up request transmission" state to the "idle" state, and
deletes the output side of the bypass pipe management table, such
that eventually no bypass pipe is set up.
[0211] Next, detailed control message sequences to be used at a
time of bypass pipe release are shown in FIGS. 19, 20, and 21,
where FIG. 19 shows a control message sequence for a case in which
the bypass pipe is released by a router at an entrance of the
bypass pipe, and FIG. 20 shows a control message sequence for a
case in which the bypass pipe is released by a router in a middle
of the bypass pipe. In either case, the release is not a partial
one and the bypass pipe is to be entirely released. FIG. 21 shows a
control message sequence for an exemplary case of an exceptional
processing in which the bypass pipe release request messages are
issued simultaneously from two routers.
[0212] As indicated in each of FIGS. 19, 20, and 21, a black dot
symbol in these figures represents a router which made a bypass
pipe release request command. Also, a solid line with an arrow in
these figures represents a control ; message. Here, a control
message at a time of bypass pipe release is also transferred to a
neighboring router hop by hop, using a default VC provided between
the neighboring routers, just as in a case of the bypass pipe set
up request message. In addition, a rectangular enclosure with an
arrow in these figures represents a state transition inside a
router and an operation of a router at that time, where each
operation is indicated in an abbreviated format of "AR(numeral)"
whose content is also specified in the table shown in FIG. 17
described above.
[0213] Now, the detailed control message sequences of FIGS. 19, 20,
and 21 will be described in further detail one by one.
[0214] FIG. 19 is a control message sequence for a case in which a
router at an entrance of the bypass pipe issues the bypass pipe
release request command. The router-A which is the router at an
entrance of the bypass pipe changes the internal state from the
"entrance" state to a "release request (downward) transmission"
state, and deletes an entry corresponding to this bypass pipe from
the ,IP-VC correspondence table such that the transmission packet
does not use this bypass pipe. Then, the router-A transmits the
bypass pipe release request (downward) to the router-B. This
message contains the pipe ID of the bypass pipe to be released, the
VCID, and the sender address. In this case, the sender address is
the router-A.
[0215] When the bypass pipe release request message is received
from the router-A, the router-B changes the internal state from the
"relay" state to a "release request (downward) transmission" state.
Then, the router-B deletes the input side of the bypass pipe
management table, and transmits the bypass pipe release response
(upward) to the router-A while transmitting the bypass pipe release
request (downward) to the router-C. Here, the bypass pipe release
response message contains the pipe ID, the VCID, and the sender
address. In this case, the sender address is the router-B. On the
other hand, the sender address of the bypass pipe release request
message is the router-A which originally issued this message.
[0216] When the bypass pipe release request message is received
from the router-B, the router-C operates similarly as the
router-B.
[0217] When the bypass pipe release request message is received
from the router-C, the router-D changes the internal state from the
"exit" state to the "idle" state. Then, the router-D deletes the
input side of the bypass pipe management table and transmits the
bypass pipe release response message to the router-C.
[0218] When the bypass pipe release response message is received,
each of the router-C, the router-B, and the router-A changes the
internal state from the "release request (downward) transmission"
state to the "idle" state. By means of these operations, the bypass
pipe is released.
[0219] FIG. 20 is a control message sequence for a case in which a
router in a middle of the bypass pipe (assumed to be the router-B
here) issues the bypass pipe release request command. When the
bypass pipe release request command is received, the router-B
changes the internal state from the "relay" state to a "release
request (upward, downward) transmission" state. Then, the router-B
deletes the ATM routing table in order to finish the ATM transfer,
and transmits the bypass pipe release request (upward) packet to
the router-A while transmitting the bypass pipe release request
(downward) message to the router-C.
[0220] The router-C and the router-D operate similarly as in a case
of FIG. 19.
[0221] When the bypass pipe release request (upward) is received
from the router-B, the router-A changes the internal state from the
"entrance" state to the "idle" state. Then, the router-A deletes
the virtual next hop IP address of the IP routing table by looking
up the user in the bypass pipe management table in order to switch
the IP packet transfer from the bypass pipe to the default VC.
Also, the router-A deletes the entry for this bypass pipe from the
IP-VC correspondence table while deleting the output side of the
bypass pipe management table. Then, the router-A finishes its
operation by transmitting the bypass pipe release response
(downward) message to the router-B.
[0222] When the bypass pipe release response (downward) is received
from the router-A, the router-B changes the internal state from the
"release request (upward, downward) transmission" state to the
"release request (upward) transmission" state. Then, the router-B
finishes its operation by deleting the input side of the bypass
pipe management table.
[0223] FIG. 21 is a control message sequence for an exemplary case
of an exceptional processing at a time of the bypass pipe release,
in which the bypass pipe release request messages are issued
simultaneously from the router-A and the router-B. At a time of
issuing the bypass pipe release request messages from the router-A
and the router-B, the operations are the same as in the normal
cases described above.
[0224] When the bypass pipe release request message is received
from the router-A, the router-B changes the internal state from the
"release request (upward, downward) transmission" state to the
"release request (downward) transmission" state, and deletes the
input side of the bypass pipe management table.
[0225] On the other hand, when the bypass pipe release request
message is received from the router-B, the router-A changes the
internal state from the "release request (downward) transmission"
state to the "idle" state, and deletes the output side of the
bypass pipe management table.
[0226] The procedures and the internal operations for the bypass
pipe set up and release described above can be summarized in terms
of the state transitions inside the router as shown in FIG. 22. It
is to be noted that, in the above description, the procedures and
the internal operations for the bypass pipe set up and release have
been described only for a normal case in which the packet reaches
without a failure. However, in practice, there is also a
possibility for the packet to be lost. For this reason, a timer is
activated whenever the request message is transmitted, such that
when there is no response to that message within a prescribed
period of time (i.e., a case of time-out), a new operation is to be
carried as indicated in FIG. 22.
[0227] In FIG. 22, each node (enclosure) represents the internal
state of the router, and there are nine internal states altogether.
The solid lines with arrows among these internal states represent
the state transitions. Each solid line with an arrow is accompanied
by the indication of an event causing that state transition and an
operation at that time. For instance, when the bypass pipe set up
command arrives in the "idle" state, the internal state is changed
to the "idle & set up request transmission" state, and the
operation AS1 is carried out. Also, in FIG. 22, "!P1" and "!P2"
indicate negations of the above described conditions P1 and P2,
i.e., cases in which the conditions P1 and P2 do not hold,
respectively.
[0228] It is to be noted here that, although not depicted in this
state transition diagram of FIG. 22, in practice, when the router
is in any of the "entrance" state, the "relay" state, and the
"exit" state, whether the bypass pipe is connected is checked
regularly, and it is necessary to return to the "idle" state
whenever the bypass pipe is not connected.
[0229] Next, with references to flow charts of FIGS. 23 and 24, an
exemplary bypass pipe set up procedure using control message
exchanges in an exemplary situation shown in FIG. 25 will be
described.
[0230] In FIG. 25, ATM-LANs 11 to 15 (#1 to #5) are inter-networked
by routers 1A, 1B, and 1C having network layer processing units,
where each network layer processing unit corresponds to the network
layer processing unit 35 in a configuration of FIG. 5. In this
example, there are a default VC 10.times. with VCI=$x between the
router 1A and the router 1B and a default VC 10a with VCI=$a
between the router 1B and the router 1C, and a bypass pipe formed
by a dedicated VC 10y with VCI=$y and a dedicated VC 10b with
VCI=$b is to be set up from the router 1A to the router 1C.
[0231] First, when the bypass pipe set up request is recognized
(step S2001), the router 1A looks up the internal routing table
(step S2002) and transmits the bypass pipe set up request message
to a next stage router 1B (step S2003) in order to set up the
dedicated VC between this router 1A and the next stage router 1B.
Here, the bypass pipe set up request message is to be transferred
hop by hop between the neighboring routers, so that it is always
transmitted through the default VC between the neighboring
routers.
[0232] In this embodiment, the VP pipe is established between the
neighboring routers, and the default VC and the dedicated VC to be
used for the datagram transfer are both contained in this VP. In
this case, the bypass pipe set up request message contains at least
(1) the IP address of the start point router, (2) the IP address of
the end point router, and (3) the VCI value desired to be used
within the VP pipe.
[0233] For example, in a case the router 1A desires to establish
the bypass pipe, the router 1A captures the VCI value "$y" of the
dedicated VC within the VP between this router 1A and the router
1B, and transmits the datagram via that dedicated VC (step
S2004).
[0234] Here, the router 1A may start the transmission of the
datagram toward the router 1C through this VC with VCI=$y
immediately, or at a certain period of time after the sending of
the message, or after a message reception acknowledgement is
received from the router 1B side in some way. As will be described
below, in any of these cases, this VC has the network layer
processing unit in a middle of the route as the receiving target,
so that even if this VC is not connected with the end point router
end-to-end, it is possible to transmit the datagram through this
VC. At this point, VCI=$y is going to be registered as the
destination datalink layer identifier (VPI/VCI value in this
embodiment) of the router 1C on the routing table within the router
1A. Here, however, the metric value remains unchanged and does not
decrease even when the dedicated VC is established.
[0235] The router-B receives the bypass pipe set up request message
through the default VC between the router 1A and the router 1B as
described above (step S2005). By means of this message, the
router-B can recognize the fact that "it is requested to establish
this VC with VCI=$y as the bypass pipe to the router 1C in the VP
containing the default VC". At this point, the L2 routing table of
the datalink layer switch unit 202 within the router 1B may be set
up such that the connection target of this VC with VCI=$y is set as
the network layer processing unit within the router 1B, or the
connection target may be as the network layer processing unit
within the router 1B for all VCI values within the VP in advance at
a time of the VP establishment (step S2006). At this point, the VC
with VCI=$y in this VP is connected to the network layer processing
unit within the router 1B so that it is not ATM transfer, but it is
possible even at this point to transmit the datagram through this
VC to reach the router 1C eventually.
[0236] Next, with regard to the end point router of the bypass pipe
set up request message, the network layer processing unit of the
router 1B searches the next hop router by looking up its own
routing table (step S2007). In a case this router 1B is the relay
router (step S2008 NO), the router 1B selects the next hop router
which is the router 1C by looking up the routing table (step
S2009). Then, the router 1B captures a still unused VCI value ($b
for example) in the VP between this router 1B and the router 1C,
and transmits the bypass pipe set up request message through the
default VC to the next hop router IC by rewriting the desired VCI
value of the above (3) to Sb (step S2010).
[0237] Here, at the router 1B, it is possible to generate the
dedicated VC by directly connecting this VC and the VC with VCI=$y
in the VP between the router 1A and the router 1B at the ATM layer.
Here, the direct connection at the ATM layer is realized by
directly setting up the header conversion table of the add/drop and
header conversion unit 32 as described above in a case the network
layer processing unit which received the bypass pipe set up request
message itself is the two port router, or by directly setting up
the the switch table in the switch input/output processing unit as
described above in a case the network layer processing unit which
received the bypass pipe set up request message itself is the
multi-port router, or by directly issuing the primitive for the set
up to the processing function governing the table set up (step
S2011). One of the feature of the present invention lies in this
point.
[0238] This table set up may be carried out immediately after the
reception of the bypass pipe set up request message, or at a
certain period of time after the message has been sent out to the
next stage router, or after a message reception acknowledgement is
received from the next stage router in some way.
[0239] FIG. 25 shows a situation (intermediate state) of the
default VC and the dedicated VC for the datagram transfer using the
router 1A as the start point after the above described procedure
has been carried out.
[0240] Up to now, the procedure for setting up or releasing a
bypass pipe using a hard state scheme has been described according
to the control message sequences as outlines in parts (b) and (e)
of FIG. 13. Alternatively, it is also possible to carry out the set
up or the release of a bypass pipe according to the control message
sequences as outlined in parts (c) (set up-2) and (d) (release-1)
of FIG. 13, where a part (c) of FIG. 13 shows a control message
sequence for the set up which is similar to that of a part (e) of
FIG. 13 for the release as described above, while a part (d) of
FIG. 13 shows a control message sequence for the release which is
similar to that of a part (b) of FIG. 13 for the set up.
[0241] More specifically, the control message sequence as outlined
in a part (c) of FIG. 13 is a case in which the bypass pipe is set
up step by step using sequential exchange of the bypass pipe set up
request message and the bypass pipe set up response message between
each neighboring routers.
[0242] In this case, when the router-A requests the setup of the
bypass pipe, the router-A transmits the bypass pipe set up request
message to the router-B. In response, if the set up of the
requested bypass pipe is to be permitted, the router-B transmits
the bypass pipe set up response message to the router-A. By means
of this, the router-A can recognize that the dedicated VC has been
set up between the router-A and the router-B, so that the router-A
makes the setting to transmit the data packets through this newly
set up dedicated VC. At this point, the dedicated VC has not been
set up beyond the router-B yet, so that the router-B carries out
the conventional network layer transfer to the router-C.
[0243] Next, the router-B determines whether to set up the bypass
pipe between this router-B and the next stage router-C as well, and
in a case of setting up such a bypass pipe. the router-B transmits
the bypass pipe set up request message to the router-C. Then, when
the bypass pipe set up response message from the router-C is
received, the router-B makes the setting to carry out the datalink
layer transfer within this router-B between the dedicated VC for
the packet transfer from the router-A to the router-B and the
dedicated VC for the packet transfer from the router-B to the
router-C. By means of this, the bypass pipe has been set up from
the router-A to the router-C, and the transfer at the router-B can
be switched from the conventional network layer transfer to the
faster datalink layer transfer.
[0244] Here, whether or not to transmit the bypass pipe set up
request message to a next stage router can be determined by manners
similar to those for determining a timing for bypass pipe set
up/release which will be described in detail below.
[0245] By repeating the similar operation at the router-C as well,
it is possible to set up the bypass pipe from the router-A to the
router-D.
Bypass Pipe Set Up/Release Procedure (Soft State)
[0246] Next, a procedure for setting up or releasing a bypass pipe
using a soft state scheme in this embodiment will be described in
detail.
[0247] In short, this scheme operates as follows. In this scheme,
the transmitting side router can transmit the bypass pipe set up
request message regularly at a certain time interval. Then, the
router at an intermediate stage of the bypass pipe is given a
time-out value for the bypass pipe, such that this time-out value
is reset by the reception of the bypass pipe set up request
message, for example. By means of this, it is possible to prevent
the bypass pipe that is no longer used from being left as a
garbage. Alternatively, the router at an intermediate stage of the
bypass pipe can monitor a presence or absence of the cell traffic
in each bypass pipe, and when there is no traffic in some bypass
pipe over a certain period of time, it judges that this bypass pipe
is no longer used and resets this bypass pipe, i.e., changes the
reception target of the VC constituting that bypass pipe to the
router processing unit within this router and resets the
information concerning the transmission source and the reception
target for that VC. In this manner, the similar effect as described
above can also be achieved.
[0248] Here, it is not necessary for the bypass pipe set up request
message to carry a set up request for just one bypass pipe per one
message, and it is possible for a single message to carry set up
requests for a plurality of bypass pipes. In general, a number of
bypass pipes can trace the identical route in a course of reaching
to their respective end point routers, so that it is useful to
carry set up requests for a plurality of dedicated VCs in the
bypass pipe set up request message from viewpoints of the reduction
of the traffic and the ease of the management. In particular, in a
case of requesting the set up of a plurality of bypass pipes at
once as in a case of the abnormality to be described below, this
scheme is also useful in preventing the occurrence of the
congestion at the CPU within the router and the network.
[0249] Now, the bypass pipe set up/release procedures in this
scheme will be described in detail.
[0250] In an exemplary case in which a router-A commands set
up/release of a bypass pipe from a router-A to a router-D through a
router-B, a router-C, and ATM-LANs provided between routers as
shown in a part (a) of FIG. 26, there are two possible outlines for
a control message sequence to be used at a time of set up as
indicated in parts (b) and (c) of FIG. 26, and two possible
outlines for a control message sequence to be used at a time of
release as indicated in parts (d) and (e) of FIG. 26.
[0251] Here, a case of using the control message sequence as
outlined in a part (b) (set up-1) of FIG. 26 which is the receiver
initiative soft state type bypass pipe control protocol will be
described in detail first. In this case, the bypass pipe management
table of FIG. 18C described above should be modified to include an
additional "previous router" field for registering an IP address of
a previous stage router, which is to be registered at a time of
receiving the path message, and to be utilized in determining a
path of the bypass pipe.
[0252] In this case, the router-A regularly transmits a path
message toward the router-D in order to permit the bypass pipe up
to the router-D and notify the path of the bypass pipe to the
intermediate routers. Each of the router-B and the router-C which
are the intermediate routers in this example transfers this message
to its next stage router, while registering the IP address of its
previous stage router into the previous router field of the bypass
pipe management table in order to record the path. Thus, the
router-B registers the IP address of the router-A, and the router-C
registers the IP address of the router-B, while the router-D which
received the path message registers the IP address of the router-C
into the previous stage router field of the bypass pipe management
table.
[0253] When the router-D wishes to utilize the bypass pipe, the
router-D transmits a reservation message to the address registered
in the previous stage router field of the bypass pipe management
table, which is the router-C in this example. IN the bypass pipe
management table, the dedicated VC to be used as the bypass pipe is
registered in the input side. This reservation message is
transmitted regularly, and a timer T1 (not shown) is activated
whenever this reservation message is transmitted, such that the
same message is transmitted again when this timer indicates the
time-out.
[0254] When the reservation message is received from the router-D,
the router-C checks the condition P3: this router is not the first
router of the bypass pipe. When this condition P3 is checked, the
router-C transmits the reservation message to the previous stage
router-B, while rewrites the ATM routing table to enable the ATM
transfer between the dedicated VC from the router-B to the router-C
and the dedicated VC from the router-C to the router-D. In
addition, the router-C registers the dedicated VCs into the input
side and the output side of the bypass pipe management table, and
activates a timer T2 (now shown) in order to monitor, the fact that
the reservation message is regularly transmitted.
[0255] The router-B operates similarly as the router-C, and
transfers the reservation message to the router-A. When the
reservation message is received from the router-B, the router-A
recognizes that it is the first router of the bypass pipe by
checking the condition P3, and registers the dedicated VC to the
output side of the bypass pipe management table, while changing the
IP routing table and the IP-VC correspondence table. Then, the
router-A activates the timer T2 in order to monitor the fact that
the reservation message is regularly transmitted. By means of these
operations, the bypass pipe from the router-A to the router-D can
be set up.
[0256] A case of using the control message sequence as outlined in
a part (c) (set up-2) of FIG. 26 which is the sender initiative
soft state type bypass pipe -control protocol can also be realized
similarly as in a case of the receiver initiative soft state type
bypass pipe control protocol described above.
[0257] As for the bypass pipe release procedure in this scheme,
there are two methods including a method for sending an explicit
release message, and a method for releasing the bypass pipe when
the timer indicates the time-out as the regularly transmitted
reservation messages stop arriving. The control message sequences
as outlined in a part (d) (release-1) and a part (e) (release-2) of
FIG. 26 belong to the former method of sending an explicit release
message.
[0258] In a case of a part (d) of FIG. 26 for releasing from the
router-A side, the router-A changes the internal state from the
"entrance" state to the "idle" state. Then, the router-A deletes
the output side of the bypass pipe management table as well as the
virtual next stage router from the IP-VC correspondence table and
the IP routing table, and stops the timer T2. Then, the router-A
notifies the release explicitly to the router-B by sending the
release message.
[0259] When the release message is received from the router-A. the
router-B changes the internal state from the "relay" state to the
"idle" state. Then, the router-B deletes the dedicated VC related
to the bypass pipe to be released from the input side and the
output side of the bypass pipe management table, rewrites the ATM
routing table in order to stop the ATM transfer, and stops the
timer T2. Then, the router-B sends the release message to the next
router-C.
[0260] The router-C operates similarly as the router-B, and sends
the release message to the router-D.
[0261] When the release message is received from the router-C, the
router-D changes the internal state from the "exit" state to the
"idle" state. Then, the router-D deletes the input side of the
bypass pipe management table, and stops the timer T1.
[0262] A case of a part (e) of FIG. 26 for releasing from the
router-D side can also be realized similarly as in a case of a part
(d) of FIG. 26 described above.
[0263] In this case, the router-D changes the internal state from
the "exit" state to the "idle" state, and sends the release message
to the router-C. Then, the router-D deletes the input side of the
bypass pipe management table, and stops the timer T1.
[0264] When the release message is received from the router-D, the
router-C changes the internal state from the "relay" state to the
"idle" state, deletes the input side and the output side of the
bypass pipe management table, and rewrites the ATM routing table.
Then, the router-C sends the release message to the router-B, and
stops the timer T2.
[0265] The router-B operates similarly as the router-C, and sends
the release message to the router-A.
[0266] When the release message is received from the router-B, the
router-A changes the internal state from the "entrance" state to
the "idle" state. Then, the router-A deletes the output side of the
bypass pipe management table as well as the virtual next stage
router from the IP-VC correspondence table and the IP routing
table, and stops the timer T2.
[0267] In the above, a case of explicit release has been described,
but there is also a case in which the release message packet is
lost in a middle, so that it is necessary to make it possible to
release the bypass pipe by using a local timer. Namely, the
reservation message is to be regularly transmitted from the exit
router while the bypass pipe is active, so that when it is
recognized that the reservation message has stopped arriving, the
bypass pipe can be released.
[0268] To this end, each router has the timer T2, which is reset
whenever the reservation message arrives. When the reservation
message has stopped arriving and this timer T2 indicates the
time-out, the router changes the internal state to the "idle"
state, and deletes the bypass pipe management table along with the
ATM routing table, the IP routing table, and the IP-VC
correspondence table relates to this bypass pipe.
[0269] The procedures and the internal operations for the receiver
initiative soft state type bypass pipe set up and release described
above can be summarized in terms of the state transitions inside
the router as shown in FIG. 27.
[0270] In FIG. 27, each node (circular enclosure) represents the
internal state of the router, and there are four internal states
altogether. The solid lines with arrows among these internal states
represent the state transitions. Each solid line with an arrow is
accompanied by the indication of an event causing that state
transition and an operation at that time. Here, each operation is
indicated in an abbreviated format of "A(numeral)" whose content is
specified in a table shown in FIG. 28 similar to the table of FIG.
17 described above.
[0271] Similarly, the procedures and the internal operations for
the sender initiative soft state type bypass pipe set up and
release described above can be summarized in terms of the state
transitions inside the router as shown in FIG. 29 similar to the
state transition diagram of FIG. 27. Here, each operation is
indicated in an abbreviated format of "B(numeral)" whose content is
specified in a table shown in FIG. 30 similar to the table of FIG.
17 described above.
[0272] Next, with reference to the flow chart of FIG. 31, the
operation of the router in a case of a change in the routing table
of the router due to the routing protocol operation will be
described. Here, the change of the routing table includes a case
corresponding to a change of the topology of the internet
environment, a case corresponding to a change of the metric value
that can happen in a case of an abnormality such as the breakdown
of an intermediate router or ATM-LAN, etc.
[0273] In the following, a case in which the bypass pipe route is
changed will be described. In this case, the change of the routing
table is handled as follows.
[0274] For the neighboring router, when the router processing unit
of the router recognizes an occurrence of an abnormality such as a
case in which the routing information that is supposed to be
transmitted regularly fails to arrive, or a case in which a
calculation result of the metric value has increased (step S4002),
this router processing unit rewrites the L2 routing table for the
dedicated VC connected toward that neighboring router, to make this
router processing unit itself as the reception target of that VC
(step S4004). Consequently, as for the datagram received from that
VC which had been the dedicated VC until then, the transfer is
continued according to this updated routing table in that router
processing unit.
[0275] Here, if this dedicated VC becomes out of use as the routing
information according to the existing routing protocol such as RIP
is transmitted toward the upstream side of this dedicated VC, and
the routing route has changed subsequent to the recognition of the
abnormality on the upstream side, the registered information on
this dedicated VC will be eventually deleted within a certain
period of time by the time-out, etc. caused as the bypass pipe set
up request message that is supposed to be transmitted regularly
fails to arrive, or as the traffic stops existing in that VC.
[0276] On the other hand, when the "entrance" state router
recognized the change of the routing table (step S4002 YES and step
S4007 YES), the bypass pipe set up request message is issued
according to the newly rewritten routing table in this router.
Thereafter, the bypass pipe set up procedure is carried out again
according to the procedure of FIGS. 23 and 24 described above, for
example (step S4008). Then, the datagram can be transmitted through
this newly set up bypass pipe.
[0277] At a time of the breakdown of the network or the router at
an intermediate stage, the changes can occur in a plurality of
routing tables at once, so that the bypass pipe setup request
message to be newly issued makes a plurality of set up requests for
the bypass pipes in an identical direction simultaneously within
this message. By means of this, it is possible to reduce a number
of bypass pipe set up request message packets within the network,
while the processing function (such as CPU) within the router for
handling this message can handle these requests within this single
message, so that it is also possible to reduce a processing load
and achieve a quick recovery.
[0278] It is to be noted that a case of explicitly sending the
bypass pipe set up request message has been described above, but it
is also possible for the start point router to immediately start
transmitting the datagram through an unused VC of the new route. In
this case, the algorithm of FIGS. 40 and 41 to be described below
is going to be employed.
Bypass Pipe Set Up Procedure (In-band)
[0279] Next, a procedure for setting up or releasing a bypass pipe
using an in-band scheme for handling the control messages will be
described in detail. In this scheme, the control packet for
commanding the bypass pipe set up/release os transferred through
the dedicated VC to be used as a constituent element of that bypass
pipe itself, that is, the data packet and the control packet are
transferred by the identical dedicated VC.
[0280] FIG. 32 shows a control message sequence for the bypass pipe
set up in this scheme, for an exemplary case of setting up the
bypass pipe from the router R2 to the router R4 through the router
R3 and the ATM-LANs between the routers as indicated in a part (a)
of FIG. 32. In this case, as indicated in a part (b) of FIG. 32, at
a time of the bypass pipe set up, the router R2 for commanding the
set up of the bypass pipe from the router R2 to the router R4
transmits the "Bypass Pipe Setup" message to the router R3 through
the dedicated VC-A. When this "Bypass Pipe Setup" message is
received from the router R2, the router R3 transmits the "Bypass
Pipe Setup" message to the router R4 through the dedicated VC-B. In
response, the router R4 transmits the "Bypass Pipe Ack" message to
the router R3 through the dedicated VC-B, and then the router R3
transmits the "Bypass Pipe Ack" message to the router R2 through
the dedicated VC-B. By means of these operation, the bypass pipe
from the router R2 to the router R4 as indicated in a part (c) of
FIG. 32 is established.
[0281] As for the bypass pipe release. the cell flow is monitored
at each router, and the bypass pipe is released by the judgement of
each router using appropriate timer in this scheme.
Case of Using SVC
[0282] Up to this point, it has been assumed that the VC is given
in a form of a PVC. However, it is also possible for the VC to be
given in a form of an SVC (Switched Virtual Channel).
[0283] In a case of using the SVC, the bypass pipe set up procedure
can be realized in any of the following four methods.
[0284] (1) After the ATM signaling is completed, the control
messages are transmitted in the same direction by the same
procedure as in a case of using the PVC described above.
[0285] (2) After the control messages are transmitted, the ATM
signaling is carried out in an opposite direction.
[0286] (3) After the ATM signaling is completed, the control
messages are transmitted in an opposite direction.
[0287] (4) The bypass pipe set up message is embedded into the ATM
signaling message.
[0288] The method (1) is a method which uses the SVC but the SVC is
handled similarly as the PVC by setting up the VC in advance.
[0289] It is noted here that it has been assumed in the above
description that the default VC and some dedicated VCs are set up
for the bypass pipe control in advance, but it is also possible to
provide a VP of a prescribed capacity between the routers in
advance instead. In such a case, the operations since the VC is
established in the VP until the VC is released are the same as a
communication scheme utilizing the VC.
[0290] In addition, instead of providing the VPs in mesh shape
among all the routers in advance, it is also possible to utilize an
SVP (Switched VP) in which the VP is connected between the routers
by the ATM signaling upon an arrival of the data packet to be
communicated (which makes the first VC request between these
routers). In this case, the operations since the VP is connected by
the ATM signaling until the VP is disconnected is the same as a
communication scheme utilizing the VP.
[0291] The method (2) is a method which establishes the bypass pipe
by using the bypass pipe set up request message. Here, the
algorithm is similar to that shown in FIGS. 23 and 24 described
above.
[0292] In this case, the first stage router generates the bypass
pipe set up request message. Then, this message is forwarded to the
next stage router by using the default VC according to the routing
table provided in the router (steps S2001 to S2004 of FIG. 23).
[0293] When this message is received, the router of an intermediate
stage establishes the link layer connection (ATM connection in this
embodiment) between this router and the previous stage router,
while forwarding that message to the next stage router (Steps S2005
to S2010). In addition, the VC established between this router and
the previous stage router is connected at the ATM layer with the VC
established (by the next stage router) between this router and the
next stage router by the setting of the L2 routing table (step
S2011 of FIG. 24).
[0294] The last stage router establishes the link layer connection
between this router and the previous stage router, and sets the
router processing unit within this router as the terminal point of
that connection (step S2006).
[0295] By means of a series of these operations, the bypass pipe
can be set up in this method (2). In short, this is a method in
which the establishment of the bypass pipe is sequentially
requested to the next stage router explicitly by means of the
bypass pipe set up request message.
[0296] The method (3) is a method in which the establishment of the
datalink layer connection is carried out by the previous stage
router, rather than the next stage router as in the method (2)
described above. More specifically, this method can be carried out
according to the flow charts of FIGS. 33 and 34 as follows.
[0297] When the bypass pipe set up request is recognized, the
datalink layer switch unit of the first stage router-A which wishes
to establish the bypass pipe recognizes the next stage router by
looking up the routing table within that router, and requests the
establishment of the bidirectional VC between this router and the
next stage router to the ATM-LAN (steps S7001 to S7003). Here, the
requested VC is a bidirectional VC because the InARP message to be
described below will be transmitted in an opposite direction in
which case. At this point, a special message such as the bypass
pipe set up request message is not issued.
[0298] Then, the intermediate stage router-B receives the bypass
pipe set up request from the ATM-LAN in which the sub-net is shared
with the previous stage router-A (step S7006). Here, at this point,
the use of this VC is unknown and the end point IP address to be
the start point of this VC is also unknown, so that the router-B
generates the InARP request message and transmits this InARP
request message to this VC (step S7007).
[0299] Then, when the InARP request message reaches to the
router-A, the router-A returns its own IP address as the InARP
response message, along with a destination sub-net ID of that VC
indicating that it wishes to use this link layer connection (VC) as
the dedicated VC between this router and a particular sub-net
identified by that sub-net ID either as a part of the InARP
response message or as a separate message from the InARP response
message, through that VC (step S7004). In the former case, it is
necessary to adopt a special format for the InARP response
message.
[0300] When this InARP response message is received, the router-B
recognizes that VC as the dedicated VC for the packets destined to
that particular sub-net (step S7008). In addition, by looking up
the routing table within that router, the router-B requests the
establishment of the VC to the ATM-LAN connected with the next
stage router-C (step S7011). Also, when that VC is established and
it is recognized by the next stage router that this VC is for the
bypass pipe, the VC of the previous stage and this VC are directly
connected at the ATM layer by the setting of the L2 routing table
within that router, such that these VCs can be passed through by
only the ATM layer processing (step S7012).
[0301] The final stage router-C recognizes that the VC requested to
be set up to it is that for the bypass pipe with this router as the
end point (S7008) according to the InARP response message (or a
message following the InARP message) by carrying out the above
described steps S7006-S7008, and as this router is an "exit" router
(step S7009 YES), this router connects that VC to the network layer
processing unit within this router (step S7010).
[0302] In this case, it should be noted that an ID of the sub-net
to be the terminal point of the bypass pipe is entered into the
InARP response message (or a separate message).
[0303] By means of a series of these operations, the bypass pipe
can be set up in this method (3).
[0304] It is to be noted that this method (3) uses the
bidirectional VC, so that the dedicated VC given in a form of the
bidirectional VC is going to be produced. Hence, in order to
prevent a plurality of such bidirectional dedicated VC to be set up
between any two routers, when one bypass pipe set up procedure is
carried out in one direction while another bypass pipe set up
procedure is also carried out in an opposite direction
simultaneously such that the dedicated VC to the target sub-net has
already been established in that one direction by the procedure in
the opposite direction at some intermediate stage router, this
intermediate stage router may directly connect these VCs at the ATM
layer by the setting of the L2 routing table, so as to reduce time
required for the bypass pipe set up considerably and simplify the
bypass pipe set up procedure.
[0305] The method (4) is a method which carries out the bypass pipe
set up by utilizing the ATM signaling. Here, for the ATM signaling,
the so called well known VC for the ATM signaling is utilized.
[0306] In FIG. 35, several control message sequences for the bypass
pipe set up and release in this method are shown for an exemplary
case of setting up or releasing the bypass pipe as indicated in a
part (e) of FIG. 35 from the router R2 to the router R4 through the
router R3 and the ATM-LANs provided between the routers as
indicated in a part (a) of FIG. 35. Here, each ATM-LAN has a call
control device 605 for handling the ATM signaling therein.
[0307] As the control message sequence for the bypass pipe set up,
three sequences are shown in parts (b), (c), and (d) of FIG.
35.
[0308] In the set up-1 shown in a part (b) of FIG. 35, the SETUP
message of the ATM signaling is sequentially transmitted through
the call control devices 605, from the router R2 to the router R3
first, and then from the router R3 to the router R4. After that,
the CONNECT message of the ATM signaling is sequentially
transmitted through the call control devices 605, from the router
R4 to the router R3 first, and then from the router R3 to the
router R2. When the CONNECT message is returned to the router R2,
the bypass pipe set up is completed.
[0309] In the set up-2 shown in a part (c) of FIG. 35, the SETUP
message of the ATM signaling is transmitted through the call
control device 605-1 from the router R2 to the router R3. When the
SETUP message is received from the router R2, the router R3
transmits the SETUP message through the call control device 605-2
to the router R4 while at the same time the router R3 also
transmits the CONNECT message through the call control device 605-1
to the router R2. When the SETUP message is received from the
router R3, the router R4 transmits the CONNECT message to the
router R3. When these CONNECT messages reached to the router R2 and
the router R3, respectively, the bypass pipe set up is
completed.
[0310] In the set up-3 shown in a part (d) of FIG. 35, after the
control message sequence similar to the set up-2 described above is
carried out, the router R4 transmits the Bypass Pipe Ack message
which is an independent control message different from those of the
ATM signaling. When this Bypass Pipe Ack message is received at the
router R2, the bypass pipe set up is completed.
[0311] On the other hand, as the control message sequence for the
bypass pipe release, two sequences are shown in parts (f) and (g)
of FIG. 35.
[0312] The release-1 shown in a part (f) of FIG. 35 is similar to
the set up-1 described above in that the REL (release) message of
the ATM signaling is sequentially transmitted through the call
control devices 605, from the router R2 to the router R3 first, and
then from the router R3 to the router R4. After that, the RELCOM
(release complete) message of the ATM signaling is sequentially
transmitted through the call control devices 605, from the router
R4 to the router R3 first, and then from the router R3 to the
router R2. When the RELCOM message is returned to the router R2,
the bypass pipe is released.
[0313] The release-2 shown in a part (g) of FIG. 35 is similar to
the set up-2 described above in that the REL message of the ATM
signaling is transmitted through the call control device 605-1 from
the router R2 to the router R3. When the REL message is received
from the router R2, the router R3 transmits the REL message through
the call control device 605-2 to the router R4 while at the same
time the router R3 also transmits the RELCOM message through the
call control device 605-1 to the router R2. When the REL message is
received from the router R3, the router R4 transmits the RELCOM
message to the router R3. When these RELCOM messages reached to the
router R2 and the router R3, respectively, the bypass pipe is
released.
[0314] It is to be noted that the bypass pipe set up and the bypass
pipe release are totally independent operations so that any desired
combination of the above described control message sequences for
the set up and the control message sequences for the release may be
adopted.
Timing for Switching to Bypass Pipe
[0315] As for the timing for switching the data packet transfer
from the usual IP transfer to the ATM level transfer using the
bypass pipe, the following two cases can be considered.
[0316] (i) The data packet transfer is switched to that using the
bypass pipe after the bypass pipe is set up all the way to the
target node.
[0317] (ii) The data packet transfer is switched to that using the
bypass pipe for any part of the bypass pipe that has been
established by then, as the bypass pipe is sequentially set up
between each neighboring nodes.
[0318] As for the handling of the data packets before the data
packets can be transmitted through the bypass pipe, the following
two cases can be considered.
[0319] (i) The data packets are transferred by using the default VC
before the bypass pipe set up is completed.
[0320] (ii) the data packets are kept awaiting at an entrance of
the bypass pipe until it becomes possible to transfer the data
packets through the bypass pipe.
[0321] In a case of using the connection-less network layer
protocol as in the current IP, either one of the above (i) or (ii)
for the data packet transfer switching timing can be used, while it
seems preferable to transfer the data packets by using the default
VC before the bypass pipe set is completed.
[0322] In a case of the connection oriented network layer protocol,
however, it seems preferable to transfer the data packets by using
the bypass pipe after the bypass pipe set up is completed up to the
target node as far as the data packet transfer switching timing is
concerned, while it seems appropriate to keep the data packets
awaiting at an entrance of the bypass pipe until it becomes
possible to transfer the data packets through the bypass pipe as
far as the data packet handling before the data packet can be
transmitted through the bypass pipe. Here, however, it is assumed
that the connection set up request at the network layer level is to
be encapsulated within the control message for the bypass pipe set
up.
Timing for Bypass Pipe Set Up/Release
[0323] Here, the timing for starting the above described bypass
pipe set up/release procedure in this embodiment will be
explained.
[0324] Each node can recognize a need to set up the bypass pipe and
transmit the control message in the following situations.
[0325] (1) When a statistical value calculated at that node has
reached to a prescribed value.
[0326] (2) When any of the following messages is received:
[0327] (i) RSVP message (Path message, Reservation message,
etc.);
[0328] (ii) ST II message (Connect message, Accept message,
etc.);
[0329] (iii) TCP syn or fin message.
[0330] (3) When there is an instruction from the application (such
as an instruction which requests a securing of a bandwidth or a QoS
by an IP layer or an upper layer of the host, for example).
[0331] (4) When it is recognized that the bypass pipe has not been
set up at a time of packet transmission.
[0332] Also, each node can recognize a need to release the bypass
pipe in the following situations.
[0333] (1) When a statistical value calculated at that node has
reached to a prescribed value.
[0334] (2) When there is an instruction from the application (such
as an instruction which requests a securing of a bandwidth or a QoS
by an IP layer or an upper layer of the host, for example).
[0335] Here, it is to be noted that, in a case of dealing with the
hard state type protocol as in a case of the ST II, the bypass pipe
is released only by the explicit release request, whereas in a case
of dealing with the soft state type protocol as in a case of the
RSVP (Resource Reservation Protocol), in addition to the release of
the bypass pipe at a time of receiving the explicit release
request, the bypass pipe can also be released by each router on the
route individually when each router stops receiving the regularly
transmitted bandwidth maintaining request (Refresh message in the
RSVP).
[0336] Now, with reference to an exemplary configuration shown in
FIG. 36, various types of nodes which can utilize the bypass pipe
in this embodiment will be explained. Here, for an exemplary case
of transmitting the data packet through the bypass pipe from left
to right in the figure, the following nodes may have a need to set
up the bypass pipe between the router R2 and the router R4.
[0337] (1) A non-ATM transmission side host or application (such as
the host Hi).
[0338] (2) An ATM transmission side host or application (such as
the host H3).
[0339] (3) An initial stage cell switching router (such as the
router R2).
[0340] (4) An intermediate stage cell switching router (such as the
router R3).
[0341] (5) A final stage cell switching router (such as the router
R4).
[0342] (6) An ATM reception side host or application (such as the
host H4).
[0343] (7) A non-ATM reception side host or application (such as
the host H2).
[0344] Among them, (1) can be realized in the ST II for example,
while (7) can be realized in the RSVP for example. The others can
be realized by means of the bypass pipe control messages.
[0345] Now, some exemplary cases of the timing for starting the
bypass pipe set up procedure will be described in detail.
[0346] (A) Case of Using Statistical Information
[0347] First, a case of using the statistical information in
determining the timing for starting the bypass pipe set up
procedure will be described. This function can be realized by the
datalink layer connection set up judgement unit 205 in the
configuration of FIG. 4 described above.
[0348] This datalink layer connection set up judgement unit 205
commands the set up or release of the datalink layer connection
according to the statistical information obtained by the network
layer switch unit 204, and updates the datalink layer routing table
in the datalink layer switch unit 202 to reflect that statistical
information. Here, when more packets than a prescribed number are
received, transmitted, or transferred, the datalink layer
connection is set up and this connection is registered in the
datalink layer routing table. Also, when no packet arrives over a
prescribed period of time, the datalink layer connection is
released, and this connection is deleted from the datalink layer
routing table.
[0349] More specifically, this operation is carried out according
to the flow chart of FIG. 37 as follows.
[0350] In this case of FIG. 37, there is provided a network layer
packet statistical information t5 which indicates a number of
received packets as a count value to be updated whenever the packet
is transferred at the network layer switch unit 204. The datalink
layer connection set up judgement unit 205 looks up this network
layer packet statistical information (step S31), and if the-count
value (COUNT) is greater than a constant value (CONST1) (step S32
YES), the datalink layer connection (L2 connection) is set up (step
S33), and an entry for this connection is registered in the
datalink layer routing table (L2 routing table) (step S34). Also,
if the count value (COUNT) is less than another constant value
(CONST2) (step S35 YES), the datalink layer connection (L2
connection) is released (step S36), and an entry for this
connection is deleted from the datalink layer routing table (L2
routing table) (step S37). Then, the network layer packet
statistical information t5 is reset (step S38), and after a wait
for a prescribed timer time set by a timer (not shown) (step S39),
the above operation is repeated.
[0351] Here, by setting CONST1=1 for example, it is possible to
carry out the packet transfer for the first packet alone, and then
switch to the cell transfer for the subsequent packets.
[0352] Also, as a method for releasing the datalink layer
connection, it is possible to adopt a method in which a certain
time value (CONST3) is set as the count value (COUNT) in the
network layer packet statistical information t5 whenever a packet
is received, and sequentially reduced as time elapses, such that
the datalink layer connection is released when the count value
becomes 0.
[0353] Also, instead of using the network layer packet statistical
information as described above, it is also possible to use the
statistical information for the datalink layer data in a similar
manner to release the datalink layer connection.
[0354] (B) Case of Set Up at a Time of Router Activation
[0355] Next, a case of starting the bypass pipe set up procedure
when a connection target router is activated will be described. In
this case, the operation is carried out according to the flow chart
of FIG. 38 as follows.
[0356] When the routing information is transmitted from the
neighboring router (step S1001), the router can recognize that a
new router has appeared at several hops ahead, and that this new
router has not been connected to the same ATM-LAN as this router
according to its metric value.
[0357] Then, this router checks whether the default VC between this
router and the neighboring router has been established (step
S1002), and if not, this router establishes the default VC for the
datagram transfer between this router and the neighboring router
(step S1003). Then, this router carries out a mutual confirmation
using the user-user data, or a mutual confirmation using the
signaling data element, or a mutual confirmation using InARP, with
respect to the neighboring router (step S1004). Meanwhile, the
routing information transmitted from the neighboring router is
registered into the routing table in this router (step S1005).
[0358] Then, this router produces a correspondence table for the
layer 3 address and the layer 2 address/VPI/VCI (step S1006). This
correspondence table corresponds to a table of X FIG. 8 described
above or tables of FIGS. 18D and 18E described above.
[0359] At this point, when this router recognizes that there exists
a sub-net which is not connected by the direct end-to-end ATM
connection at several hops ahead, this router checks if it is
possible to establish the bypass pipe (step S1007), and if so, the
bypass pipe set up procedure as described above is carried out
(step S1008) to establish the direct end-to-end ATM connection
between this router and that new router, and then the datagram
transmission by using that bypass pipe is carried out (step
S1009).
[0360] (C) Case of Set Up at a Time of Packet Transmission
[0361] Next, a case of starting the bypass pipe set up procedure at
a time of the packet transmission will be described. In this case,
the operation is carried out according to the flow chart of FIG.
39, where the steps identical to those in the flow chart of FIG. 7
described above are given the same reference numerals in the figure
and their descriptions will be omitted.
[0362] The operation according to FIG. 39 differs from that of FIG.
7 in that, after the dedicated VC search at the step S9 has failed,
before the default VC search at the step S10 is carried out,
whether or not to set up the dedicated VC is judged (step S21).
Then, if the dedicated VC is to be set up, the dedicated VC setup
procedure is carried out (step S22) and the operation proceeds to
the step S12, whereas otherwise the default VC search at the step
S10 is carried out.
[0363] (D) Case of Set Up at a Time of Resource Reservation
Protocol Reception
[0364] Next, a case of starting the bypass pipe set up procedure
when a resource reservation protocol (such as RSVP, ST II, etc.)
for the network layer is received will be described.
[0365] In this case, the bypass pipe set up procedure is carried
out when the set up message of the resource reservation protocol is
received, and the bypass pipe release procedure is carried out when
the release message of the resource reservation protocol is
received. Here, in a case the resource reservation protocol is the
RSVP, the session ID of the RSVP may be used as the bypass pipe
ID.
[0366] It is noted here that it is also possible to set up or
release the bypass pipe according to the set up or release command
of the transport layer protocol such as TCP, instead of the
resource reservation protocol. In general, it is possible to set up
or release the bypass pipe according to the connection set up or
release message at the layer above the network layer.
Bypass Pipe Set Up/Release Procedure Using No Control Message
[0367] Next, the bypass pipe set up/release procedures without
using any control message in this embodiment will be described in
detail.
[0368] First, with references to the flow charts of FIGS. 40 and
41, the first bypass pipe set up/release procedure using no control
message will be described.
[0369] When the first stage router receives the datagram destined
to the sub-net which is several hops ahead, to which the bypass
pipe has not been set up and for which the direct delivery is not
supported by this router (step S3001), in order to establish the
bypass pipe up to that sub-net, this router looks up the routing
table in this router to check the next stage router (step S3002),
and captures one arbitrary unused VC to the next stage router other
than the default VC within the VP connected to the next stage
router (step S3003). Then, the datagram destined to that sub-net is
transmitted through that VC (step S3004).
[0370] At the subsequent stage router, the terminal point of each
unused VC between this router and the neighboring router is set in
advance as the network layer processing unit in this router (step
S3005) such that the receiving targets of all the VCs within the VP
for datagram transfer are set in the L2 routing table in
advance.
[0371] Then, the second stage router which received the datagram
destined to some unregistered sub-net through the VC other than the
default VC from the first stage router (step S3006) recognizes that
the previous stage router wishes to use that VC as the dedicated VC
destined to the destination sub-net of the received datagram, as
this datagram is received from the VC other than the default
VC.
[0372] Then, unless this second stage router is the final stage
router of this dedicated VC (step S3007 NO), this second stage
router looks up the routing table in this router to check the next
stage router (S3009), captures one arbitrary unused VC to the next
stage router other than the default VC within the VP connected to
the next stage router and transmits the datagram destined to that
sub-net through that VC (step S3010), while this VC between the
second stage router and the third stage router is directly
connected at the ATM layer with the VC between the first stage
router and the second stage router by an appropriate setting in the
L2 routing table (step S3011).
[0373] The third and subsequent intermediate stage routers also
operate similarly as the second stage router.
[0374] When the destination sub-net of the datagram received from
the unused VC is a sub-net for which the direct delivery is
supported by this router, the router recognizes that it is the
final stage router to which the dedicated VC is destined, so that
this VC is registered as the bypass pipe destined to this router,
and the transfer target of the received datagram is set to be the
network layer processing unit in this router (step S3008).
[0375] By means of these operations, it is possible to construct
the bypass pipe environment without using any bypass pipe set up
request message. In this procedure, the bypass pipe is constructed
only at the route in which the datagram to be transmitted actually
exists, so that there is an advantage that a wasteful set up
operation for a bypass pipe which is actually not going to be used
can be eliminated.
[0376] Next, with references to FIG. 42 to FIG. 48, the second
bypass pipe set up/release procedure using no control message will
be described.
[0377] The following description is based on an exemplary
configuration as shown in FIG. 42 in which the ATM-LANs 603 have
switches 604 (604a to 604e) connecting the routers 601 (router-A
and router-B) and the terminals 602 (host Hi and host H2) to the
ATM-LANs 603, where the switch 604a provides a VC (PVC) between the
host HI and the router-A, the switches 604b and 604c provide a VC
(PVC) between the router-A and the router-B and the switches 604d
and 604e provide a VC (PVC) between the router-B and the host
H2.
[0378] In this case, each terminal 602 has a configuration as shown
in FIG. 43, which is basically similar to that of FIG. 9 and which
comprises: an ATM layer processing unit 621; and ATM cell-IP packet
conversion unit 622 connected with the ATM layer processing unit
621; an IP layer processing unit 623 connected with the ATM cell-IP
packet conversion unit 622, and a VC management unit 624 and a
destination management unit 627 connected with the IP layer
processing unit 623, where the VC management unit 624 includes a VC
control unit 625 and a VC management table 626, while the
destination management unit 627 includes a destination control unit
628 and a destination management table 629.
[0379] On the other hand, each router 601 has a configuration as
shown in FIG. 44, which comprises: an ATM layer processing unit 611
(corresponding to the datalink layer switch unit 202 of FIG. 4);
and ATM cell-IP packet conversion unit 612 (corresponding to the
datalink layer-network layer translation unit 203 of FIG. 4)
connected with the ATM layer processing unit 611; an IP layer
processing unit 613 (corresponding to the network layer switch unit
204 and the network layer control unit 207 of FIG. 4) connected
with the ATM cell-IP packet conversion unit 612: and a bypass pipe
management unit 617 connected with the ATM layer processing unit
611 and the IP layer processing unit 613 and a VC management unit
614 connected with the IP layer processing unit 613 (corresponding
to the the datalink layer connection set up judgement unit 205 and
the datalink layer control unit 206 of FIG. 4), where the VC
management unit 614 includes a VC control unit 615 and a VC
management table 616, while the bypass pipe management unit 617
includes a bypass pipe control unit 618 and a bypass pipe
management table 619.
[0380] Here, the switches 604a to 604e have route control tables
with initial settings as indicated in FIG. 45A to FIG. 45E,
respectively, while the host Hi, the host H2, the router-A, and the
router-B have the VC management tables 616 with initial settings as
indicated in FIG. 46A to FIG. 46D, respectively.
[0381] Now, with reference to the flow chart of FIG. 47, a
procedure for the data packet transmission by the transmission
terminal 602 in this case will be described first.
[0382] When data to be transmitted is generated (step S101), the
destination management table 629 is referred to check if there
exists an entry corresponding to the destination IP address in the
generated IP packet (S102). In a case a corresponding entry exists
at the step S102, a corresponding I/F and a corresponding VPI/VCI
are obtained from the destination management table 629 (step S103).
Then, the ATM cell is assembled according to a prescribed format
(step S107) and the data packet, i.e., the assembled ATM cell, is
transmitted (step S108).
[0383] In a case a corresponding entry does not exist at the step
S102, a next hop is determined by referring to an IP routing table
provided within the IP layer processing unit 623 (step S104), where
the IP routing table registers the correspondence between the
destination IP address and the next hop IP address.
[0384] Then, the VC management table 626 is referred to obtain
available I/F and VPI/VCI corresponding to the next hop (step
S105), and the status field in the VC management table 626
corresponding to the obtained I/F and VPI/VCI is updated while the
destination management table 629 is updated by adding a new entry
(step S106). Then, the ATM cell is assembled according to a
prescribed format by adding the obtained VPI/VCI (step S107) and
the data packet, i.e., the assembled ATM cell, is transmitted (step
S108).
[0385] Next, with reference to the flow chart of FIG. 48 a
procedure for the data packet handling by the router 601 in this
case will be described.
[0386] When the data packet (ATM cell) is received (step 511), the
bypass pipe management table 619 is referred by the ATM layer
processing unit 611 (step S112) to check if there exists a bypass
pipe corresponding to the I/F and the VPI/VCI of the received ATM
cell (step S113).
[0387] In a case the corresponding bypass pipe exists at the step
S113, the ATM level exchange is executed at the ATM layer
processing unit 611 (step S114), and the data packet (ATM cell) is
transmitted to the bypass pipe by only the ATM level processing
(step S116).
[0388] In a case the corresponding bypass pipe does not exist at
the step S113, the ATM cell is disassembled and given to the IP
layer processing unit 613, to determine a next hop according to the
IP routing table provided therein. Then, the VC management table
616 is referred to obtain available I/F and VPI/VCI corresponding
to the next hop, according to the IP address of the next hop. Then,
the ATM cell is assembled again by adding the obtained VPI/VCI
(step S115) and the data packet, i.e., the assembled ATM cell, is
transmitted (step S116).
[0389] At the same time, the bypass pipe control unit 618 registers
a set of the I/F and the VPI/VCI at times of reception and
transmission of that ATM cell into the bypass pipe management table
619, to produce a new bypass pipe while updating the bypass pipe
management table 619. By means of this operation, the subsequent
ATM cells having the same transmission source and the same
destination arriving to this router after this updating of the
bypass pipe management table 619 can be transferred at high speed
by only the ATM level processing at the ATM layer processing unit
611.
[0390] In a case the VC cannot be obtained for some reasons such as
a lack of bandwidth or an occurrence of obstruction, the ATM cell
loss will be caused. It is also possible to keep the subsequent ATM
cells awaiting in a buffer (now shown) provided in the ATM layer
processing unit 611 until the bypass pipe management table 619 is
updated.
[0391] Here, the VC is basically bidirectional, so that when each
of the terminal 602 and the router 601 obtains the VCID, if any
unused VCID is secured at random, there is a possibility for the
same VCID to be secured from both sides. In order to prevent such a
case in which the same VCID is secured from both sides, it is
possible to determine in advance a VCID of the VC given by a PVC
that can be secured from a node on one side.
[0392] The deletion of the entry from the bypass pipe management
table 619 can be realized by a method using the ATM level message
such as the OAM cell which is different from the control message at
the network layer level, or by a method for deleting the entry
according to a statistical information such as a traffic on the
bypass pipe.
[0393] Next, with references to FIG. 49 to FIG. 51, the third
bypass pipe set up/release procedure using no control message will
be described.
[0394] In the second procedure described above, the VCs of the same
function are setup between the terminal 602 and the router 601 as
well as between the routers 601. In this third procedure, the
default Vc and the dedicated VC are set up between the terminal 602
and the router 601 as well as between the routers 601. Then, a
sender who wishes to make the conventional IP level transfer of the
data packet at the router 601 utilizes the default VC for the data
packet transmission, while a sender who wishes to make the ATM
level transfer of the data packet at the router 601 as much as
possible utilizes the dedicated VC for the data packet
transmission.
[0395] In this case, each terminal 602 has a configuration similar
to that shown in FIG. 43 described above, except that the VC
management table 626 in the VC management unit 624 has an internal
configuration as shown in FIG. 49, which includes a default VC
management table 6261 for registering a VPI/VCI of a VC defined in
advance as the default VC for each VC connection target and an
other VC management table 6262 for registering a VPI/VCI of a VC
other than the default VC. Similarly. each router 601 has a
configuration similar to that shown in FIG. 44 described above,
except that the VC management table 616 in the VC management unit
614 has an internal configuration similar to that shown in FIG. 49,
which includes a default VC management table 6161 for registering a
VPI/VCI of a VC defined in advance as the default VC for each VC
connection target and an other VC management table 6162 for
registering a VPI/VCI of a VC other than the default VC.
[0396] Now, with reference to the flow chart of FIG. 50, a
procedure for the data packet transmission by the transmission
terminal 602 in this case will be described first.
[0397] When data to be transmitted is generated (step S121), the
destination management table 629 is referred to check if there
exists an entry corresponding to the destination IP address in the
generated IP packet (S122). In a case a corresponding entry exists
at the step S122, a corresponding I/F and a corresponding VPI/VCI
are obtained from the destination management table 629 (step S123).
Then, the ATM cell is assembled according to a prescribed format
(step S130) and the data packet, i.e., the assembled ATM cell, is
transmitted (step S131).
[0398] In a case a corresponding entry does not exist at the step
S122, a next hop is determined by referring to an IP routing table
provided within the IP layer processing unit 623 (step S124), and
whether the ATM transfer is wished as much as possible or not is
decided (step S125).
[0399] When it suffices to make the conventional IP level transfer
(step S125 NO), the default vC management table 6261 in the VC
management table 626 is referred to obtain I/F and VPI/VCI
corresponding to the next hop (step S128), and the destination
management table 629 is updated (step S129). Then, the ATM cell is
assembled according to a prescribed format (step S130) and the data
packet, i.e., the assembled ATM cell, is transmitted (step
S131).
[0400] On the other hand, when it is wished to make the ATM level
transfer as much as possible (step S125 YES), the other VC
management table 6262 in the VC management table 626 is referred to
obtain available I/F and VPI/VCI corresponding to the next hop
(step S126), and the other VC management table 6262 and the
destination management table 629 are updated (step S127). Then, the
ATM cell is assembled according to a prescribed format (step S130)
and the data packet, i.e., the assembled ATM cell, is transmitted
(step S131).
[0401] Next, with reference to the flow chart of FIG. 51 a
procedure for the data packet handling by the router 601 in this
case will be described.
[0402] When the data packet (ATM cell) is received (step S141), the
bypass pipe management table 619 is referred to check if there
exists a bypass pipe corresponding to the I/F and the VPI/VCI of
the received ATM cell (step S142).
[0403] In a case the corresponding bypass pipe exists at the step
S142, the ATM level exchange is executed at the ATM layer
processing unit 611 (step S143), and the data packet (ATM cell) is
transmitted to the bypass pipe by only the ATM level processing
(step S150).
[0404] In a case the corresponding bypass pipe does not exist at
the step S142, the ATM cell is disassembled and given to the IP
layer processing unit 613 (step S144), and a next hop is determined
according to the IP routing table provided in the IP layer
processing unit 613 (step S145).
[0405] Then, when the received ATM cell is a cell transmitted from
the default VC (step S146 YES), the default VC management table
6161 in the VC management table 616 is referred to obtain I/F and
VPI/VCI corresponding to the next hop, according to the IP address
of the next hop (step S147). Then, the ATM cell is assembled again
by adding the obtained VPI/VCI (step S149) and the data packet,
i.e., the assembled ATM cell, is transmitted (step S150).
[0406] On the other hand, when the received ATM cell is a cell
transmitted from the dedicated VC (step S146 NO), the other VC
management table 6162 in the VC management table 616 is referred to
obtain available I/F and VPI/VCI corresponding to the next hop,
according to the IP address of the next hop (step S148). Then, the
ATM cell is assembled again by adding the obtained VPI/VCI (step
S149) and the data packet, i.e., the assembled ATM cell, is
transmitted (step S150).
[0407] At the same time, the bypass pipe control unit 618 registers
a set of the I/F and the VPI/VCI at times of reception and
transmission of that ATM cell into the bypass pipe management table
619, to produce a new bypass pipe while updating the bypass pipe
management table 619. By means of this operation, the subsequent
ATM cells having the same transmission source and the same
destination arriving to this router after this updating of the
bypass pipe management table 619 can be transferred at high speed
by only the ATM level processing at the ATM layer processing unit
611.
Multi-Point to Point Bypass Pipe Set Up/Release Procedure
[0408] Next, the bypass pipe set up/release procedures for a
multi-point to point connection in this embodiment will be
described in detail.
[0409] The following description is based on an exemplary
configuration as shown in FIG. 52 in which the ATM-LANs 111 to 118
are inter-networked by the routers 11A to 11F, where the ATM-LANs
111 to 118 have sub-net IDs equal to #1 to #8, respectively.
[0410] In this case, the operation of the node (router) 11A for
transmitting the bypass pipe set up request is the same as that
described in conjunction with FIG. 23 above.
[0411] On the other hand, the next stage router 11B operates
according to the flow chart of FIG. 53 as follows.
[0412] When the bypass pipe set up request message is received from
the router 11A (step S6005), the router 11B captures the VCI value
of the dedicated VC from the previous stage router 11A and sets the
network layer processing unit of that router as the terminal point
of that dedicated VC (step S6006).
[0413] Then, the router 11B analyzes the terminal sub-net of the
received bypass pipe set up request message (step S6007) to
determine whether to transfer this message to the next stage router
or not (step S6008).
[0414] In a case of transferring this message, whether the bypass
pipe to the terminal sub-net has already been established or not is
determined (step S6009), and when the bypass pipe has already been
established, that dedicated VC is directly connected to that bypass
pipe at the ATM layer level by an appropriate setting in the L2
routing table, so as to become a multiplexing point for that
dedicated VC (step S6010).
[0415] On the other hand, when the bypass pipe has not been
established, the routing table is looked up to determine the next
stage router (step S6011), and the bypass pipe set up request is
transferred to the next stage router (step S6012). Then, the router
11B captures the VCI value of the bypass pipe to the next stage
router, and directly connects the VCI values of the bypass pipe and
that dedicated VC at the ATM layer level by an appropriate setting
in the L2 routing table (step S6013).
[0416] Here, in a course of the bypass pipe set up, especially when
a number of routers to pass is numerous, it is possible to
encounter a situation in which the VC directly connected at the ATM
layer exists up to an intermediate stage router but it has not
reached to the final stage router yet. In such a case, the L2
routing table in the router may have a setting in which the
connection target of the VC in a process of being generated is set
to the network layer processing unit in that router.
[0417] By means of this, the datagram is transferred only by the
ATM layer up to that router as the datagram can pass through the
other routers up to that router by the ATM layer processing alone,
so that compared with the hop by hop datagram transfer, the high
speed datagram transfer is possible even during the bypass pipe set
up process.
[0418] Also, in this case, the timing for switching the connection
target of the VC from the network layer processing unit of the
router to the next stage VC, i.e., the timing for rewriting a
header conversion table or a switch table (L2 routing table) in the
router, can be set to a time at which one packet has passed through
that VC, it is possible to prevent an occurrence of a packet
destruction (a situation in which only a part of the packet is
transferred to the router while the other part of the packet is
transferred to the next stage router via the bypass pipe) at this
switching timing. For example, in a case of carrying out the ATM
cell assembling of the datagram by using the AAL (ATM Adaptation
Layer) type 5, this switching timing can be learned from the
user-user data field of the ATM cell, so that it suffices to carry
out the table rewriting when this switching timing is
recognized.
[0419] Next, a set up of a multi-point to point bypass pipe in a
case in which a number of ATM-LANs to be inter-networked has
increased will be described.
[0420] When the router 11E and the router 11F are activated, the
router 11E establishes the default VC between the router 11B and
this router 11E, while the router 11F establishes the default VC
between the router 11C and this router 11F, and the operation such
as the routing information exchange is carried out through these
default VCs. By means of the routing information exchange, the
routers 11E and 11F recognize the existence of the router 11A at
several hops ahead, and an establishment of the bypass pipe to this
router 11A is attempted, as in the steps S3001 to S003 of FIG. 40
described above.
[0421] Actually, the router 11F recognizes the existence of the
router 11B (sub-nets #2 and #5), the router 11A (sub-net #1), and
the router 11E (sub-net #7) at several hops ahead according to the
routing information exchange, so that the router 11F can transmit a
bypass pipe set up request message containing three set up requests
for three bypass pipes to these routers 11B, 11A, and 11E, to the
router 11C. The router 11E can also transmit the similar bypass
pipe set up request message to the router 11B.
[0422] In this case, when the bypass pipe set up request message
for a bypass pipe in a direction from the router 1F to the router
11A is received from the router 11F, the router 11C operates as
follows.
[0423] Here, as shown in FIG. 54, the router 11C already has a
bypass pipe 131 between the router 11A and this router 1C.
Consequently, the multiplexing of the bypass pipes is carried out
within the router 11C. In other words, the when the VC for the
bypass pipe from the router 11F is captured, the router 11C merges
this VC to the bypass pipe 131 from the router 11C to the router
11A that has already been established earlier. Namely, the VC from
the router 11F to the router 11A and the VC from the router
processing unit in this router 11C to the router 11A are both
connected to the bypass pipe 131 from the router 11C to the router
11A by using a table in the add/drop and header conversion unit
within this router 11C (or a switch table in a case of a multi-port
router).
[0424] Similarly, when the bypass pipe set up request message for a
bypass pipe in a direction from the router 11E to the router 11A is
received from the router 11E, the router 11B utilizes the bypass
pipe 131 to the router 11A that has already been established in
this router 11B, by merging the VC for the bypass pipe from the
router 11E to the bypass pipe 131 by an appropriate setting of a
table in the add/drop and header conversion unit within this router
11B (or a switch table in a case of a multi-port router), such that
the datagram from the router 11E can reach to the router 11A by
only the ATM layer processing.
[0425] Thus, in this case, as shown in FIG. 55, the bypass pipes
from the router processing units in the routers 11E and 11F are
merged at the router 11B to effectively form a spanning tree with
the router 11A as a root and the other routers as nodes.
[0426] Hence, the multi-point to point connection obtained in this
procedure is obtained by the merging of the connections in the
routers, and not by a use of a multi-point connection of the
ATM-LAN. Consequently, this multi-point to point ATM connection can
be realized by the protocol among the routers alone, and the
datalink layer is not necessarily required to have a function of a
multi-point connection.
[0427] As described, in this procedure, it is possible to form the
multi-point to point ATM connection as shown in FIG. 55 in which
each router functions as a root (destination) and the other routers
functions as leaves (start point).
[0428] Here, the cell flow from this multi-point to point ATM
connection is merged at each router functioning as a node, the
multiplexing of the datagram is necessary, and the following should
be taken into account.
[0429] First, in a case of using the ALL type 3/4, a different MID
(Multiplex Identifier) should be assigned to the source of each
datagram. By means of this, it becomes possible for the router 11A
to identify each transmission source.
[0430] Second, in a case of using the AAL type 5, the transmission
source identification at the cell level is impossible at the router
11A, so that the add/drop function in the router or the ATM switch
should be provided with such a function that, in a given VC, until
a transmission of one AAL-PDU (datagram) is finished, the other
PDUs are not allowed to flow into that given VC.
[0431] In the multi-point to point ATM connection obtained by this
procedure, each router functions as a root (destination) and the
branch points (nodes) of this multi-point to point ATM connection
are located at the routers. In this manner, it becomes possible to
realize the dedicated Vc with a smaller number of VCs (or more
specifically, a smaller number of ATM-LANs inter-networked to one
ATM-LAN).
[0432] Thus, in this procedure, the spanning tree for the datagram
transfer which is generated by the routing protocol operating among
the routers is directly realized by the multi-point to point
connection formed by the ATM connections. Note here that, within
each ATM-LAN, each of these multi-point to point VCs is basically
the point to point VC, which may be a VC associated with QoS.
[0433] In this procedure, as a plurality of datagrams from a
plurality of locations are multiplexed into one VC at the router,
there is a possibility for an overflow of the VC capacity or a cell
loss within the ATM switch to occur, in a case of the traffic
concentration. Such an overflow or a cell loss can be prevented by
any of the following measures.
[0434] (1) For the VC in which the congestion or the cell loss is
likely to occur, the relay of the cell to that VC by only the ATM
layer processing can be temporarily or partially interrupted and
the routing to the router processing unit is used instead.
[0435] (2) For the lower stream of the spanning tree (i.e., at a
side closer to the terminal point router), a larger bandwidth
resource can be secured in advance compared with the upper
stream.
[0436] (3) Basically, the cell loss occurs at the router which
becomes a node of the spanning tree. Consequently, an ATM switch in
such a router can be selectively formed by a high performance
switch capable of realizing the lower cell loss rate compared with
the ATM switch in the ATM-LAN.
[0437] It is to be noted that, besides those already mentioned
above, many modifications and variations of the above embodiments
may be made without departing from the novel and advantageous
features of the present invention. Accordingly, all such
modifications and variations are intended to be included within the
scope of the appended claims.
* * * * *