U.S. patent application number 14/249405 was filed with the patent office on 2014-08-07 for packet switch and switching method for switching variable length packets.
This patent application is currently assigned to HITACHI, LTD.. The applicant listed for this patent is HITACHI, LTD.. Invention is credited to Takeshi AIMOTO.
Application Number | 20140219288 14/249405 |
Document ID | / |
Family ID | 13939877 |
Filed Date | 2014-08-07 |
United States Patent
Application |
20140219288 |
Kind Code |
A1 |
AIMOTO; Takeshi |
August 7, 2014 |
Packet Switch and Switching Method for Switching Variable Length
Packets
Abstract
A packet switch for switching variable length packets, wherein
each of output port interfaces includes a buffer memory for storing
transmission packets, a transmission priority controller for
classifying, based on a predetermined algorithm, transmission
packets passed from a packet switching unit into a plurality of
queue groups to which individual bandwidths are assigned
respectively, and queuing said transmission packets in said buffer
memory so as to form a plurality of queues according to
transmission priority in each of said queue groups, and a packet
read-out controller for reading out said transmission packets from
each of said queue groups in the buffer memory according to the
order of transmission priority of the packets while guaranteeing
the bandwidth assigned to the queue group.
Inventors: |
AIMOTO; Takeshi;
(Sagamihara-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HITACHI, LTD. |
Tokyo |
|
JP |
|
|
Assignee: |
HITACHI, LTD.
Tokyo
JP
|
Family ID: |
13939877 |
Appl. No.: |
14/249405 |
Filed: |
April 10, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12550508 |
Aug 31, 2009 |
8730962 |
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14249405 |
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10197464 |
Jul 18, 2002 |
7602783 |
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12550508 |
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09280980 |
Mar 30, 1999 |
6570876 |
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10197464 |
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Current U.S.
Class: |
370/412 |
Current CPC
Class: |
H04L 49/9063 20130101;
H04L 49/90 20130101; H04L 47/525 20130101; H04L 49/205 20130101;
H04L 47/10 20130101; H04L 49/3009 20130101; H04L 47/521 20130101;
H04L 49/3027 20130101; H04L 47/50 20130101; H04L 47/2441 20130101;
H04L 47/528 20130101 |
Class at
Publication: |
370/412 |
International
Class: |
H04L 12/873 20060101
H04L012/873 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 1998 |
JP |
10-088330 |
Claims
1. A communication apparatus for forwarding a plurality of packets
through input ports and output ports, the communication apparatus
comprising: a buffer memory; a classifier which performs a
classification of a packet the plurality of packets received
through the input ports, by classifying the packet into one of a
plurality of queue groups, in accordance with either at least one
of a transport layer protocol and a layer protocol of an OSI (Open
Systems Interconnection) reference model higher than a transport
layer of the packet; a queuing controller which queues the packet
into the buffer memory based on a result of the classification by
the classifier; a packet read-out controller which reads a packet
classified into another queue group other than a specific queue
group using a bandwidth of a first bandwidth that is unused while
guaranteeing the first bandwidth assigned to the specific queue
group; and a packet sending unit which sends each of the plurality
of packets read from the buffer memory to one of the output
ports.
2. The communication apparatus according to claim 1, wherein the
layer protocol higher than the transport layer is at least one of
HTTP (Hyper Text Transfer Protocol), FTP (File Transfer Protocol),
TELNET (Terminal Connection) and SMTP (Simple Mail Transfer
Protocol).
Description
[0001] The present application is a continuation of application
Ser. No. 12/550,508, filed Aug. 31, 2009; which is a continuation
application of Ser. No. 10/197,464, filed Jul. 18, 2002; now U.S.
Pat. No. 7,602,783; which is a divisional application of Ser. No.
09/280,980, filed Mar. 30, 1999, now U.S. Pat. No. 6,570,876, which
claims priority from Japanese Patent Application No. 10-088330,
filed Apr. 1, 1998, the contents of which are incorporated herein
by reference.
BACKGROUND OF THE INVENTION
[0002] (1) Field of the Invention
[0003] The present invention relates to a packet switch and a
switching method, more particularly to a packet switch and a
switching method for switching variable length packets by
controlling transmission of packets according to the priority of
respective packets. More concretely, the present invention relates
to a packet switch and a switching method suitable for switching
variable length packets in the Internet, as well as intranets, and
capable for transmitting the variable length packets by controlling
a bandwidth thereof.
[0004] (2) Description of the Related Art
[0005] The packet communication is a communication method for
transmitting and receiving data in a form of a packet comprising a
predetermined format of header and a data block obtained by
dividing transmission data into blocks each having a proper length,
for example, 48 byte to 1.5 Kbytes in length. A packet switch
adopts a so-called stored and forward switching method, in which
switching of communication data is carried out after the
communication data as stored temporarily in the switch, so that it
is able to apply a variety of control to the packets passing
through the switch.
[0006] In the case of the Internet coming into wide use rapidly in
recent years, data is communicated as variable length packets with
an IP (Internet Protocol) header respectively. Therefore, a packet
switching technique is essential to each node for connecting a
network to another. An inter-networks connecting apparatus (node
apparatus) such as a router is also provided with the packet
switching function even if it is not called a "packet switch"
actually. Consequently, in the present invention, every network
apparatus provided with the packet switching function, including
the node apparatus having such a specific name as router, will be
referred to as a packet switch.
[0007] As a prior art related to such the packet switching, a
router is disclosed in Japanese unexamined Patent Publication No.
7-135512. The prior art intends to provide a router with a function
for controlling the transfer of received packets according to the
priority thereof and a function for controlling the discard of
packets performed when a buffer congestion occurs. According to the
prior art, packets received by a packet receiving unit are queued
in a buffer memory by a priority control unit according to the
transmission priority and the discard priority of each packet, then
they are transmitted to a packet transmission unit according to the
order of the transmission priority. The priority control unit
refers to a mapping table based on the transmission priority
information and the protocol information included in the header of
each received packet to obtain the processing priority and the
discard priority corresponding to the received packet, and stores
the packet in one of queues prepared corresponding to the discard
priority for each processing priority. Stored packets are output
sequentially according to the order of descending processing
priority. When the free area capacity of the buffer memory goes
under a predetermined threshold value, discard control of the
stored packets is carried out to avoid congestion. In this discard
control, packets with higher discard priority are discarded from
queues according to the order of ascending processing priority
until the free area capacity of the buffer memory reaches a target
threshold value.
[0008] In the case of the above related art, only one type of the
mapping table is referred for queuing packets. The transmission
priority and the discard priority of each packet are defined in the
mapping table corresponding to the priority information and the
protocol information included in the header of each of received
packets. Consequently, in the case of the related art, it is
difficult to control a bandwidth for each packet flow and to
provide peculiar packet switching services depending on, for
example, the source or destination network of those packets in a
node apparatus connecting a plurality of networks such as the
Internet.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a packet
switch and a packet switching method that can control a bandwidth
of each of variable length packet flows.
[0010] It is another object of the present invention to provide a
packet switch and a packet' switching method that can guarantee the
bandwidth previously reserved for each of variable length packet
flows by a communication service contract.
[0011] It is still another object of the present invention to
provide a packet switch and a packet switching method that can
perform both bandwidth control and priority control for each
variable length packet flow.
[0012] It is further another object of the present invention to
provide a packet switch and a packet switching method that can
perform both bandwidth control and priority control according to
the communication protocol of variable length packets.
[0013] In order to achieve the above objects, the packet switch of
the present invention comprises a plurality of input port
interfaces, a plurality of output port interfaces, and a packet
switching unit for switching each of variable length packets
received from the input port interfaces to one of the output port
interfaces corresponding to the destination address of the packet,
wherein each of the output port interfaces comprises a buffer
memory for storing transmission packets, a transmission priority
controller configured so as to classify the transmission packets
received from the packet switching unit based on a predetermined
algorithm and queue each of those transmission packets according to
transmission priority thereof into one of a plurality of queue
groups, each of which is assigned an individual bandwidth, a
transmission packet read-out controller for accessing the queue
groups of the buffer memory cyclically to read out transmission
packets from each of those queue groups according to the order of
descending transmission priority while guaranteeing the bandwidth
assigned to each queue group, and a packet transmission circuit for
transmitting the transmission packets read out by the transmission
packet read-out controller to an output port associated with the
output port interface.
[0014] According to an embodiment of the present invention, the
transmission priority controller is, for example, provided with
means for identifying communication service contract and
transmission priority related to each of transmission packets
according to the header information of the transmission packet
received from the packet switching unit, thereby to queue the
transmission packet in a queue corresponding to the identified
transmission priority in a queue group corresponding to the
identified communication service contract.
[0015] More concretely, the transmission priority controller
includes, for example, a first management table for defining the
identifier of the queue group corresponding to the combination of a
source network address and a destination network address and a
second management table for defining a transmission priority
corresponding to the combination of a communication protocol and a
packet priority, thereby to identify a queue group corresponding to
each of the transmission packets by referring to the first
management table based on the source network address and the
destination network address included in the header of the
transmission packet, and to identify the transmission priority of
the transmission packet by referring to the second management table
based on the communication protocol information and the packet
priority information included in the header of the transmission
packet.
[0016] According to another embodiment of the present invention,
the transmission priority controller identifies a queue group
corresponding to each of the transmission packets based on the
protocol information included in the header of the transmission
packet, then queues the transmission packet in one of the queues in
the identified queue group. In this case, for example, the object
of switching is an IP packet which is identified by the protocol of
the network layer of the OSI (Open Systems interconnection)
reference model, and transmission packets are classified into a
plurality of queue groups according to the protocol type of the
transport layer of the OSI reference model, for example, TCP
(Transmission Control Protocol), UDP (User Datagram Protocol), ICMP
(Internet Control Message Protocol), or IGMP (Internet Group
Management Protocol).
[0017] In order to guarantee the bandwidth of each queue group, the
transmission packet read-out controller of the present invention
specifies, for example, a queue group among the queue groups
cyclically to read out transmission packets, assigns a packet read
duration to the specified queue group depending on the bandwidth
thereof, and reads out transmission packets according to the order
of descending transmission priority.
[0018] Furthermore, according to an embodiment of the present
invention, the transmission packet read-out controller includes a
management table for defining a threshold value in proportion to
the bandwidth corresponding to each of the queue groups and a
control means for accessing the plurality of queue groups
cyclically to read out transmission packets continuously from each
of the queue groups, until the total length of the read out packets
exceeds the threshold value defined in the management table and for
storing the surplus length of the read out packet exceeding the
threshold value as an initial value for use in the counting of the
total packet length in the next read cycle.
[0019] The controlling means, for example, checks the initial value
for counting the total packet length associated with one of the
queue groups before reading out transmission packets from the queue
group. If the initial value exceeds its threshold value, the
controlling means subtracts the threshold value from the initial
value and switches the object of packet read out to a next queue
group without reading out any packets from the current queue group.
Consequently, variable length packets are readout to an output
port, while the bandwidth is controlled properly in a long-ranged
view.
[0020] The algorithm provided for the transmission priority
controller to classify transmission packets, as well as the
bandwidth control function provided for the transmission packet
read-out controller can be modified suitably, for example, in
response to a control command issued from an external network
management terminal.
[0021] Another feature of the packet switch of the present
invention resides in that each of the input port interfaces
comprises a receiving buffer memory for storing received packets
temporarily, a relaying priority controller configured so as to
filter the packets received from input ports based on the
destination address of the received packets, classify the filtered
received packets according to their priority based on a
predetermined algorithm, and queue those classified packets in the
receiving buffer memory according to the priority, and a received
packet read-out circuit for reading out the received packets from
the receiving buffer memory according to the order of priority to
supply those packets to the packet switching unit. By transferring
the packets according to the order of priority in both of the input
port interfaces and the output port interfaces, it is possible to
reduce the delay time of high priority packets within the packet
switch more significantly. The switching method of the present
invention for switching variable length packets comprises the steps
of: (a) filtering received packets received from an input port
based on the destination address of each of those packets; (b)
transferring the filtered packets to one of the output ports
interfaces as transmission packets according to the destination
address included in the header of each of those packets; (c)
classifying the transmission packets based on a predetermined
algorithm and queuing the classified packets according to
transmission priority into one of the a plurality of queue groups
assigned with a individual bandwidth respectively; (d) accessing
the plural queue groups cyclically to read out transmission packets
from each of those queues according to the order of transmission
priority while guaranteeing the bandwidth assigned to each of the
queue groups; and (e) transmitting the read out transmission
packets to an output port.
[0022] More specifically, the step (b) of transferring received
packets preferably includes a step (b1) of queuing received packets
according to priority in the receiving buffer and a step (b2) of
reading out the received packets stored in the receiving buffer
according to the order of priority and transferring those packets
as transmission packets to one of the output interfaces.
[0023] In the step (c) for queuing transmission packets, for
example, transmission packets are classified by communication
service contract related to each of those transmission packets and
queued in a queue group corresponding to the communication service
contract by transmission priority. Instead of this, transmission
packets may be classified by communication protocol related to each
of those transmission packets, so that those transmission packets
are queued according to transmission priority in a queue group
corresponding to the protocol thereof in the step (c).
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a block diagram indicating an embodiment of the
packet switch of the present invention.
[0025] FIG. 2 is a configuration of a network to which the packet
switch of the present invention applies.
[0026] FIG. 3 is a format of packets to be processed by the packet
switch of the present invention.
[0027] FIG. 4 is an example of a mapping table 40 for defining a
transmission priority corresponding to both protocol and priority
of each packet.
[0028] FIG. 5 is an example of a mapping table 50 for defining a
bandwidth according to both source and destination addresses of
each packet.
[0029] FIG. 6 is a drawing for explaining the layout of queues
formed according to transmission priority in a buffer area 83-1
prepared for each bandwidth.
[0030] FIG. 7 is an example of a management table provided for a
packet read-out circuit 81 shown in FIG. 1.
[0031] FIG. 8 is a flow chart showing the functions of the packet
read-out circuit 81.
[0032] FIG. 9 is a drawing for explaining the order of packets read
out by the packet read-out circuit 81.
[0033] FIG. 10 is a block diagram` showing another embodiment of
the packet read-out circuit 82-1 shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] At first, the configuration and operation of the packet
switch of the present invention will be described briefly with
reference to FIG. 1.
[0035] The packet switch 1 comprises a plurality of control boards
(10-1 to 10-L) prepared for each of input/output ports, a packet
relaying unit (packet switching unit) for relaying packets between
those control boards 10, and a management unit 9 connected to each
of the control boards 10. Each of the control boards 10 comprises
an input port interface 20 and an output port interface 21.
[0036] The input port interface 20 includes a packet receiving unit
2 for receiving packets flowing on a network from an input port IN,
a relaying priority control unit 3 for storing the packets received
from the packet receiving unit in a receiving buffer memory 72
according to the priority, and a received packet queuing unit 7 for
transferring the packets stored in the receiving buffer memory 72
to the packet relaying unit 4 according to the priority.
[0037] The output port interface 21 includes a transmission
priority control unit 5 for storing the packets received from the
relaying unit 4 selectively in one of a plurality of queue groups
formed in a transmission buffer 83 (83-1 to 83-j), a transmission
packet queuing unit 8 for reading out the packets stored in the
transmission buffer 83 according to the transmission priority while
guaranteeing the bandwidth assigned to each queue group, and a
packet transmission unit 6 for transmitting the transmission
packets read out by the transmission packet queuing unit 8 to an
output port OUT connected to a network.
[0038] The relaying priority control unit 3 is provided with a
filtering function of referencing to a routing table based on the
destination address included in the header of each received packet
to determine whether the transmission packet should be relayed to
another network or not. If it is determined that the transmission
packet should be relayed to another network, the packet is given an
output port identifier, then queued in the receiving buffer memory
72 according to the priority. More concretely, the relaying
priority control unit 3 determines a relaying priority based on the
management information (packet priority information, protocol
information, network address, etc., which will be described later
in detail with reference to FIG. 3) and stores the received packet
in a queue Qi corresponding to the determined relaying priority.
The queue Qi is one of a plurality of packet queues Q1 to Qn formed
by relaying priority in the receiving buffer memory 72.
[0039] In the received packet queuing unit 7, packets are read out
by the packet read-out circuit 71 sequentially from the queues
formed in the receiving buffer memory 72 according to the order of
descending priority, then output to the packet relaying unit 4. The
relaying unit 4 comprises, for example, a bus or crossbar switch
for switching the packets received from the receiving packet
queuing unit 7 provided in each control board 10 to one of the
other control boards identified by the output port identifier added
to the packet.
[0040] The transmission priority control unit 5 stores packets
received from the relaying unit 4 in a transmission buffer memory
83 (83-1 to 83-j) as transmission packets.
[0041] A feature of the present invention resides in that the
transmission priority control unit 5 forms a multi-dimensional
queue structure in the transmission buffer 83 by classifying
transmission packets into a plurality of groups base on the header
information of each of those packets and queuing those transmission
packets according to the transmission priority for each group.
[0042] In the illustrated embodiment, the transmission buffer 83 is
divided into a plurality of buffer areas, each of which includes a
plurality of queues (Q10 to Q1n) . . . (Qj0 to Qjn), so that a
total of j queue groups 83-1 to 83-j are formed. The transmission
priority control unit 5, as will be described later, refers to the
mapping tables 40 and 50, which will be described later with
reference to FIGS. 4 and 5, based on the control information (e.g.,
packet priority information, protocol information, network address,
etc. as will be described later in detail with reference to FIG. 3)
included in the header of each packet, thereby determining the
transmission priority and the queue group of the transmission
packet. Each of the queue groups, as will be described later, is
assigned with an individual bandwidth, and each of transmission
packets is stored in the queue Qik in one of those queue groups
corresponding to the transmission priority.
[0043] The transmission packet queuing unit 8 includes first stage
read-out circuits 82 (82-1 to 82-j) for reading out packets
according to the transmission priority from each queue group
(buffer area 83-i) and a next stage read-out circuit 81 for
outputting the packets read out by those first-stage read-out
circuits to the transmission unit 6 according to the bandwidth
assigned to each queue group.
[0044] The packet transmission unit 6 transmits packets received
from the read-out circuit 81 to an output port OUT. The output port
identifier added by the relaying priority control unit 3 to each
received packet is removed by the transmission priority control
unit 5 or the packet transmission unit 6. Grouping of transmission
packets performed by the transmission priority control unit 5 is
made, to put in the concrete, for each communication service
contract between a line provider and a network user or customer
user group. The read-out circuit 81 reads out transmission packets
sequentially from each of the queue groups so as to adapt to the
communication service level promised by each contract.
[0045] A communication service contract mentioned here means a
bandwidth guarantee contract exchanged between a network user and a
network line provider (or an Internet communication provider). More
concretely, it means a contract between a business company or a
public agency and a line provider. According to such a contract, a
communication service level including such items as communication
quality (e.g., packet delay time, delay variability, packet discard
rate, etc.), an assigned bandwidth, etc., is guaranteed for each
user. Each of those network line providers is thus responsible for
the contracted communication service level with respect to each
packet flow on the subject network.
[0046] A network manager can change the packet queuing algorithm in
the transmission priority control unit 5 and the read-out algorithm
in the read-out circuits 81 and 82 via the management unit 9 by
issuing a command, for example, from the management terminal PT
shown with a reference numeral I6Cn in FIG. 2.
[0047] The packet queuing algorithm used by the transmission
priority control unit 5 can be changed by updating the contents in
the mapping tables 40 and 50 and the packet read-out algorithm used
by the read-out circuit 81 can be changed by updating the contents
in the management table 60 as will be described later.
[0048] Next, a configuration of the packet switch of the present
invention, as well as how to use the packet switch will be
described with reference to FIG. 2.
[0049] The network shown in FIG. 2 comprises sub-networks 15An,
15Bn, 15Am, and 15Bm, and a backbone network 15Cn for connecting
those sub-networks to each other. Each of the sub-networks 15An to
15Bm is connected to packet communication terminals 16An, 16Bn,
16Am, and 16Bm respectively.
[0050] Each of the sub-networks 15An to 15Bm is provided with
packet switches 1An, 1Bn, 1Am, and 1Bm. The packet switches 1An and
1Bn are connected to a packet switches 1Cn in the network 15Cn
through the lines 14An and 14Bn respectively. The packet switches
1Am and 1Bm are connected to a packet switch 1Cm in the network
15Cn through the lines 14Am and 14Bm respectively. In the backbone
network 15Cn are connected the packet switches 1Cm and 1Cm to each
other through a line 14C.
[0051] The packet switches 1 of the present invention shown in FIG.
1 are used as packet switches 1Cn and 1Cm of the backbone network.
16Cn indicates a management terminal operated by the manager of the
network 15Cn. According to the commands issued from this management
terminal 16Cn, the control information held in the packet switches
1Cn and 1Cm, that is, the contents in the tables 40, 50, and 60 can
be updated.
[0052] Generally, a packet communication can perform a multiplex
communication, wherein a bandwidth indicating a communication
capability of a line per unit time is divided to assign the
bandwidth to a plurality of users.
[0053] In the case of the network shown in FIG. 2, the
communication 10 line 14C of the backbone network is shared by the
communication between the sub-networks 15Bn and 15Bm and the
communication between the sub-networks 15Bn and 15Bm. Packet
communication allows each line to be used effectively through the
statistical multiplexing effect by sharing a line among a plurality
of communications such way and by assigning a bandwidth to each of
those communications only when it is needed actually.
[0054] In this case, it is assumed that the communication between
the sub-networks 15An and 15Am is executed under the contract A and
the communication between the sub-networks 15An and 15Am is
executed under the contract B, and the network provider who owns
the backbone network 15C provides packet flows on the line 14C with
packet switching services according to the service levels
guaranteed by the contracts A and B. This example is equivalent to
a case in which the sub-networks 15An and 15Am are, for example, of
the head office and a branch office of a company A and the
sub-network 15Bn and 15Bm are of the head office and a branch
office of a company B, and each of those companies A and B perform
their intranet communications according to the contracts with the
Internet communication provider C.
[0055] The packet switch of the present invention provides the
following two forms of usage for a plurality of contract parties
who share the line 14C.
[0056] The first form of usage distributes the bandwidth of the
line 14C to both contracts A and B equally or with a weight
according to the contract contents respectively, through the rate
based scheduling. If there are a plurality of packet flows for the
same contract, packet switching is carried out equally for each of
those packet flows or according to the protocol and the packet
priority of each packet flow.
[0057] The second form of usage allows only one contract, for
example, the packet flow of the contract A to use the full
bandwidth of the line 14C through the head-of-line scheduling. In
this case, the guaranteed bandwidth is set as 0 for all the packet
flows of other contracts except for the contract A, and packet
switching for these contracts are carried out using the residual
bandwidth of the contract A. According to this second form of
usage, the user of a contract B can make a communication with a
less cost by using the residual bandwidth of the contract A,
although the communication quality is not guaranteed for the
contract B. If there are a plurality of packet flows for the same
contract, packet switching is carried out equally to each of the
packet flows or according to the protocol and the priority of each
packet flow just like in the first form of usage.
[0058] None of the conventional packet switches is provided with
such the function for guaranteeing communication services for
respective contracts stated, above and the function for controlling
transmission of a plurality of packet flows under the same contract
according to the priority with respect to such variable length
packets as IP packets.
[0059] FIG. 3 shows a format of the packets handled by the packet
switch of the present invention.
[0060] A packet 30 comprises a header portion 31 and a data portion
32. The header portion 31 includes packet priority information 33,
a service request 34, protocol information 35, a source address 36,
and a destination address 37. The packet priority information 33
indicates the processing priority of the packet. The service
request 34 indicates the information of a service requested by the
packet, for example, a request for reliability and high speed
performance. These items are equivalent to the priority (0 to 2nd
bits), the low delay request (3rd bit), the high through-put
request (4th bit), and the high reliability information (5th bit)
of the TOS (Type Of Service) field defined in the header of each IP
packet used for the Internet.
[0061] The protocol information 35 indicates the type of the
communication protocol used for the packet, that is, the type of
the packet. If the packet 30 is an IP packet, the protocol
information 35 identifies the type of the transport layer header 39
following the header 31. For the most frequently used protocols,
TCP (Transmission Control Protocol), UDP (User Datagram Protocol),
ICMP (Internet Control Message Protocol), and IGMP (Internet Group
Management Protocol) are well known.
[0062] The source address 36 indicates the address of a source
device from which the packet is transmitted. The destination
address 37 indicates the address of a destination device to which
the packet is forwarded. These addresses correspond to the SA
(Source IP Address) and the DA (Destination IP Address) in a case
of IP address system.
[0063] The IP address comprises an IP network address and an IP
host address. The IP network address identifies a sub-network
connected to a source or destination terminal and the IP host
address identifies the source or destination terminal. The
communication service contract described above can be identified
with the combination of such a source IP network address and a
destination IP network address.
[0064] Next, description will be made for the mapping tables 40 and
50 referred by the transmission priority control unit 5 to classify
transmission packets.
[0065] FIG. 4 shows an example of the mapping table 40 referred to
determine transmission priorities among a plurality of packet flows
transmitted under respective contracts.
[0066] The mapping table 40 is a two dimensional matrix arranging,
for example, the protocol 35 included in each packet header 31 as
column information 41 and the priority information 33 included in
the packet header 31 as row information 42, wherein a value is
assigned to indicate the transmission priority corresponding to
each combination of the priority information 33 and the protocol
35. Each value (0 to 7) of the transmission priority defined in the
mapping table 40 also indicates the value of a second index k of
the queue Qik formed in the transmission buffer area 83-i shown in
FIG. 1.
[0067] The type of the protocol 35 may be classified into, for
example, TCP and UDP according to the transport layer protocol of
the OSI reference model. It may also be classified according to a
layer upper than the transport layer, for example, into HTTP (Hyper
Text Transfer Protocol), FTP (File Transfer Protocol), TELNET
(Terminal Connection), SMTP (Simple Mail Transfer Protocol), and
etc. depending on the port number if the protocol type is TCP.
[0068] Generally, in the case of an interactive type or connection
oriented network protocol such as TCP, the source terminal
transmits a next packet after receiving an ACK packet from the
destination terminal. On the contrary, in the case of a batch type
or connectionless network protocol such as UDP, the source terminal
can transmit packets one after another without waiting for an ACK
packet from the destination terminal. Consequently, if a higher
transmission priority is given to packet flows of the interactive
type or connection oriented network protocol and a lower priority
is given to packet flows of the batch type or connectionless
network protocol in the mapping table 40, it is able to improve the
total through-put of the packet switch 1.
[0069] FIG. 5 shows a configuration of the mapping table 50
referred by the transmission priority control unit 5 to identify
the contract associated with each of the transmission packets and
to specify a queue group corresponding to the contract from among
the queue groups 83-1 to 83-j shown in FIG. 1.
[0070] The mapping table 50 is a two-dimensional matrix arranging
the source network address included in the source address 36 of
each packet header 31 as column information 51 and the destination
network address included in the destination address 37 of the
packet header 31 as row information 52, wherein an identification
number (contract identifier) of queue group is assigned
corresponding to each combination of a source network address and a
destination network address.
[0071] The reason why transmission packets are buffered in queue
groups by contract in the present invention is that reading of
packets from the transmission buffer 83 is controlled so as to
provide each transmission packet flow with a contracted bandwidth.
In the embodiment shown in FIG. 5, a contract is identified by the
combination of a source network address and a destination network
address, and the identification number of a queue group
corresponding to each contract is defined in the mapping table 50.
Each contracted bandwidth is shown in parentheses for reference in
the mapping table 50.
[0072] A queue group identification number as described above is
assumed as the value of the first index i of the queue Qik formed
in the transmission buffer area 83-i. In the illustrated example,
the communication between a terminal connected to the sub-network
Am and a terminal connected to the sub-network An is carried out
under the contract A to which the bandwidth BW1 is assigned. It
will thus be understood that packets for this contract A are queued
in the queue group 83-1. For each combination of a source network
address and a destination network address, which is not included in
any specific contract, a null indicated with a symbol "-" is set.
Packets having the address information corresponding any of such
combinations are discarded by the transmission priority control
unit 5. Discarding of such packets that are communicated between
non-contracted networks may contribute to improve the security of
the packet communication.
[0073] The transmission priority control unit 5 refers to the two
types of mapping tables 40 and 50 as described above in order to
queue transmission packets in the transmission buffer 83.
Consequently, a plurality of queue groups 83-1 to 83-j are formed
in the transmission buffer 83. Each of those queue groups 83-1 to
83-j has an identification number defined in the mapping table 50
as shown in FIG. 1. And, in each of those queue groups are formed a
plurality of queues corresponding to a transmission priority
defined in the mapping table 40 respectively as shown in FIG.
6.
[0074] Transmission packets stored in the queue groups 83-1 to 83-j
are read out by the packet read-out circuits 82-i to 82-j according
to the transmission priority for each queue group, then transmitted
to the packet transmission unit 6 by the packet read-out circuit
81, while the contracted bandwidth of each queue group is
guaranteed.
[0075] Hereunder, the operation of the packet read-out circuit 81
will be described with reference to FIGS. 7 and 8.
[0076] FIG. 7 shows a configuration of the management table 60
which is referred by the packet read-out circuit 81 to control
bandwidths. The management table 60 comprises a plurality of
records corresponding to the queue groups 83-1 to 83-j. Each of
those records comprises a queue group identification number 61, a
bandwidth 62 assigned to each queue group, and a counter area 63
for counting the length of transmission data read out from each
queue group.
[0077] FIG. 8 shows a flow chart for a control operation performed
by the packet read-out circuit 81.
[0078] The packet read-out circuit 81 initializes count values in
the counter area 63 of the management table 60 and the value of a
parameter p to zero respectively (steps 102 and 104), then
increments the value of the parameter p (step 106). After this, the
packet read-out circuit 81 compares the value of CNT(p) of the
counter 63 with the value of BW(p) of the bandwidth 62 in the p-th
record of the management table 60. If the CNT(p) is equal to or
more than the BW(p), the packet read-out circuit 81 subtracts the
value of BW(p) from the value of CNT(p) (step 120), then compares
the parameter p with the maximum value j (step 124). If the value
of the parameter p is less than the 10 maximum value j, the control
sequence returns to step 106, otherwise returns to step 106 after
clearing the value of parameter p to zero.
[0079] If the CNT(p) value is less than the BW(p) value in step
108, the packet read-out circuit 81 reads out a packet from the
p-th queue group QG(p) of the output buffer 83 and transmits the
packet to the packet transmission unit 6 (step 110). If there is no
output packet to be read out in the queue group QG(p) (step 112),
the packet read-out circuit 81 clears the counter CNT(p) value to
zero (step 122), then performs the processing of step 124. When the
packet read-out circuit 81 reads out a packet from the queue group
Qt3(p), the packet read-out circuit 81 adds the packet 20 length to
the counter CNT(p) (step 114), then returns to step 108.
[0080] FIG. 9 shows an explanatory view of a sequence of packets
read out through the read control operation described above. It is
assumed here that packets are read out from three queue groups
QG(1), QG(2), and QG(3) to which bandwidths BW(i), BW(2), and BW(3)
are assigned, respectively, for simplifying the description. The
rate of the above bandwidths is assumed to be
BW(1):BW(2):BW(3)=3:2:1.
[0081] According to the control flow chart shown in FIG. 8, the
value of parameter p is changed so that each queue group can get a
packet read cycle cyclically. Packets are read out from each queue
group continuously until the total length of read packets exceeds
the value of a contracted bandwidth BW(p) registered in the
management table 60. When the total length of the read packets
exceeds the value of the contracted bandwidth BW(p), the packet
read-out circuit 81 subtracts the contracted bandwidth BW(p) value
from the counter CNT(p) value, then transfers the packet read cycle
to next queue group. Consequently, as shown in FIG. 9, when packets
P1, P2, and P3 are read out from the first queue group QG(1), the
read cycle is transferred to the second queue group QG(2). At this
time, the counter CNT(I) value of the queue group 00(I) indicates
the length of the residual part of the packet P3 shown with a
dotted line.
[0082] When packets P4 and P5 are read out from the second queue
group QG(2), the read cycle is transferred to the third queue group
QG(3). Since the contracted bandwidth of the third queue group
QG(3) is small, the read cycle is transferred to the first queue
group QG(1) when one packet P6 is read out in this example.
[0083] When packets P7 and P8 are read out from the first queue
group QG(1), the read cycle is transferred to the second queue
group QG(2). In this example, since a long packet PS was read out
from the second queue group QG(2) in the previous read cycle, the
value of the counter CNT(2) exceeds the value of the contracted
bandwidth BW(2). Consequently, in this read cycle, no packet is
read out from the second queue group QG(2) and the read cycle is
transferred to the third queue group QG(3) after performing
subtraction on the value of the counter CNT(2). By repeating the
read operations stated above, a series of packets are sent out to
the output port OUT sequentially, in the order of P1, P2, . . . ,
P14. Thus, although the contracted bandwidth is exceeded
temporarily, as just like outputting of packets P4 and P5 from the
queue group QG(2), the contracted bandwidths of all the queue
groups are guaranteed for packet switching in a long-range
view.
[0084] According to the controlling of packet read-out described
above, if it is detected that there is no transmission packet in
any one of the queue groups, a chance to read out packets comes
round to residual queue groups in a shorter cycle. Consequently, it
becomes possible for residual queue groups to effectively use the
bandwidth assigned for the empty queue group. In addition, if all
the queue groups except one become empty, read cycles are given to
the residual queue group almost continuously. As a result, the
queue group can use the bandwidth of the output line all to itself,
thus receiving a benefit of services over its contracted level.
[0085] In FIG. 5, the j-th queue group is used to store such
transmission packets that have an extra combination of a source
network address and a destination network address other than that
correspond to bandwidth guarantee contracts registered in the table
50. For the j-th queue group, assigned is a residual bandwidth BWj
which is a residual bandwidth of the output line left by the other
contractors. The user of the residual bandwidth BWj shares the
residual bandwidth with other non-contract users, so the user can
receive a benefit of less-cost communications, although the
communication service quality is not so good.
[0086] According to the packet read-out control of the present
invention, when a bandwidth guaranteed contractor stops
communications, the bandwidth for the contractor is released to the
users of the residual bandwidth BWj. It is assumed that, as an
exaggerated example, a specific user X makes a contract for
guaranteeing the exclusive use of the full bandwidth of the output
line 14C and the residual bandwidth of the user X is assigned to
the other users. In this case, by modifying the control flow chart
shown in FIG. 8, it is also able to realize such a packet read-out
control of the head-of-line scheduling that release the full
bandwidth of the line 14C to the other users until the next packet
flow of the user X arrives whenever the packet flow of the user X
stops
[0087] In the case of such a head-of-the-line scheduling sequence,
packets are basically read out repetitively from a queue group of
the user X. If there is no packet to be read out in the queue group
of the user X, one of the other queue groups is accessed. In this
case, packets may be read out one after another by checking whether
there is a new packet arrived in the queue group of the user X each
time one packet is read out. According to the present invention,
therefore, it is possible to realize not only the first usage form,
but also the second usage form, thereby providing communication
services appropriately to both of the bandwidth contractor and
other non-contractors
[0088] The read-out circuit 82 controls the order of packets to be
read out from each queue group, for example, the order of the
packets P1, P2, P3, P7, . . . in the first queue group OG(1). In
other words, the contracted bandwidth BW(i) assigned to each queue
group is further divided by the read-out circuit 82 so as to be
assigned to a plurality of queues Oil to Qin in the queue
group.
[0089] In this case, how to assign a bandwidth to each queue is
varied widely. In the most basic method, packets are read out from
the queues in the order of descending priority and subsequent
priority queue is accessed to read out packets when the higher
priority queue becomes empty. Instead of this method, it is also
possible to assign a bandwidth to each queue according to the order
of priority beforehand, then give a different readout time to each
queue just like the method used by the read-out circuit 81. In this
case, the controlling procedure is modified so that the queue group
QG(p) is replaced with the queue Q(p) in the flow chart shown in
FIG. 8.
[0090] In order to simplify controlling of packet reading more, it
is also possible to assign the number of packets readable
continuously for each queue beforehand regardless of the packet
length so that packets are read out from the next queue when the
assigned number of packets are readout from one queue according to
the order of descending priority. It is also possible to read out
packets one by one from each queue simply according to the order of
descending priority, if necessary.
[0091] According to the flaw of output packets from the output
buffer 83 to the output port OUT, the read-out circuit 82 is
located in front of the read-out circuit 81. However, in a
viewpoint of the read-out control procedure, a queue group is
determined first by the read-out circuit 81, then the read 20 out
circuit 82 corresponding to the determined queue group reads out
packets from one of the queues in the group as shown in the flow
chart in FIG. 8.
[0092] In the packet switch shown in FIG. 1, a read-out circuit 82
is disposed for each queue group in order to make it easier to
understand the present invention. In this case, while packets are
read out from one queue group and passed to the next stage read-out
circuit 81, none of the read-out circuits 82 in other queue groups
transmits packets. Consequently, all the packets stored in the
output buffer 83 may be read out by one read-out circuit 82 by
switching over the queue groups in turn, in an actual
application.
[0093] In addition, if an address table for indicating the
addresses of the first packets of the respective queues is prepared
for each queue group and if the address table is referred in
accordance with the queue group QG(p) specified in step 110 in FIG.
8 to read out packets from a queue identified by the priority, the
functions of both read-out circuits 81 and 82 can be realized by a
processor or a dedicated hardware circuit.
[0094] FIG. 10 indicates the packet read-out circuit 82 in another
embodiment.
[0095] This packet read-out circuit 82 comprises a complete
priority type controlling circuit 821 for controlling the read out
of packets so that all the packets are read out from the first
priority queue, then from the next and subsequent priority queues
sequentially, a rate based scheduler type of controlling circuit
822 for controlling the reading out of packets so that packets are
read out from a plurality of queues in a queue group according to
each assigned bandwidth, and a selector circuit 823 for selecting
any one of the two controlling circuits according to a control
signal from the management unit 9. One of the controlling circuits
821 and 822 is activated according to the control signal from the
management unit 9. According to this embodiment, the read-out mode
of the transmission packet in the packet switch 1 can be switched
over in a moment by a command supplied from a management terminal
operated by the network manager.
[0096] In the above embodiment, description has been made for
packet switching in the network layer of the OSI reference model
represented by IP packets, but the technical concept of the present
invention may also apply to the data link layer of the OSI
reference model, thereby controlling the bandwidth for each of the
queue groups described above, for example, in an ETHERNET LAN
switch.
[0097] In the embodiment described with reference to FIG. 5, the
bandwidth of each queue group is controlled under each contract
identified from both source and destination network addresses. The
present invention may also apply to another embodiment in which the
transmission priority control unit 5 classifies transmission
packets by protocol, for example, TCP and other protocols into two
groups, and transmission packets are queued into a plurality of
queues for each queue group according to the packet priority
included in the header information of each packet. In this case,
bandwidths may be assigned to queue groups in such a manner that
the whole bandwidth of an output line is assigned only to TCP
packet flows and the residual bandwidth is assigned to the packet
flows of other protocols.
[0098] As to be understood from the above description, according to
the present invention, it is possible to provide a packet switching
in which the packet transmission priority is changed for each
network connected to the node apparatus (packet switch) in a
communication network such as the Internet in which a plurality of
networks are connected through a common line. In addition,
according to the present invention, it is also possible to provide
a packet switch and a packet switching method that can change the
transmission priority even with a communication protocol as needed
while the communication bandwidth is guaranteed for each user
according to the communication service contract.
* * * * *