U.S. patent application number 11/332180 was filed with the patent office on 2006-06-01 for mobile ip network system and connection switching method.
Invention is credited to Shoji Fukuzawa, Tetsuhiko Hirata, Susumu Matsui, Norihisa Matsumoto, Mika Mizutani, Atsushi Teshima, Masashi Yano.
Application Number | 20060114856 11/332180 |
Document ID | / |
Family ID | 16536291 |
Filed Date | 2006-06-01 |
United States Patent
Application |
20060114856 |
Kind Code |
A1 |
Hirata; Tetsuhiko ; et
al. |
June 1, 2006 |
Mobile IP network system and connection switching method
Abstract
In a mobile IP network system including a plurality of radio
access networks for connecting with mobile stations via radio links
and an IP network connected with a plurality of packet nodes for
transferring IP packets, each of the radio access networks has at
least one base station controller and at least one radio base
station connected to the base station controller. Each of the base
station controllers in the radio access network is connected to the
plurality of packet nodes to each other via a network and selects
one of the plurality of packet nodes in accordance with a state of
each mobile station to establish a logical connection to be used in
IP packet communication of the mobile station.
Inventors: |
Hirata; Tetsuhiko;
(Yokohama, JP) ; Yano; Masashi; (Fujisawa, JP)
; Matsumoto; Norihisa; (Kawasaki, JP) ; Matsui;
Susumu; (Machida, JP) ; Fukuzawa; Shoji;
(Fujisawa, JP) ; Teshima; Atsushi; (Yokohama,
JP) ; Mizutani; Mika; (Santa Clara, CA) |
Correspondence
Address: |
MATTINGLY, STANGER, MALUR & BRUNDIDGE, P.C.
1800 DIAGONAL ROAD
SUITE 370
ALEXANDRIA
VA
22314
US
|
Family ID: |
16536291 |
Appl. No.: |
11/332180 |
Filed: |
January 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09624072 |
Jul 24, 2000 |
7009950 |
|
|
11332180 |
Jan 17, 2006 |
|
|
|
Current U.S.
Class: |
370/331 |
Current CPC
Class: |
H04W 80/04 20130101;
H04W 92/24 20130101; H04L 29/06 20130101; H04W 92/02 20130101; H04W
92/12 20130101; H04W 8/26 20130101; H04W 80/00 20130101; H04W
36/0011 20130101; H04L 69/168 20130101; H04W 76/12 20180201; H04L
69/16 20130101 |
Class at
Publication: |
370/331 |
International
Class: |
H04Q 7/00 20060101
H04Q007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 22, 1999 |
JP |
11-207223 |
Claims
1. A mobile IP network system comprising: a plurality of radio
access networks each connected to mobile stations via radio links;
and an IP network to which a home agent node and a plurality of
packet nodes each for transferring IP packets destined for one of
mobile stations and received from the home agent node to one of
said radio access networks are connected, wherein each of the radio
access networks has at least one base station controller and at
least one radio base station which is connected to the base station
controller to perform radio communications with a plurality of
mobile stations, and wherein each of the base station controllers
is connected to the plurality of packet nodes through a network,
receives an identifier of the previous packet node when one of the
mobile stations moved into a control area of the base station
controller from a control area of the another base station
controller belonging to another radio access network, and selects
either the previous packet node which is communicating IP packets
for the moved mobile station with said home agent node or a
preliminarily designated specific packet node in accordance with a
communication state of the mobile station, thereby to selectively
carry out IP packet communication for the moved mobile station
between the base station controller and the previous packet node or
IP packet communication between the base station controller and the
specific packet node, after performing a registration procedure
between the moved mobile station and said home agent node,
depending on the communication state of the mobile station.
2. The mobile LP network system according to claim 1, wherein each
of said base station controllers selects, with respect to the
mobile station moved from the control area of said another base
station controller to the control area of the base station
controller, said previous packet node when the moved mobile station
is in a state of communicating IP packets with the previous packet
node and requests the previous packet node to communicate IP
packets for the moved mobile station with the base station
controller.
3. The mobile IP network system according to claim 2, wherein each
of said base station controllers has means for monitoring
communication packets of the mobile station which has moved from
the control area of said another base station controller, thereby
to close the communication between the base station controller and
the previous packet node and begin the communication between the
base station controller and the specific packet node, upon
detecting the data transmission and reception of the moved mobile
station is ceased.
4. The mobile IP network system according to claim 1, wherein said
specific packet node has means for notifying to a home agent node
of the moved mobile station which is connected to the IP network
that the mobile station is in a control area of the specific packet
node after setting of beginning the communication between the base
station controller and the specific packet node so that the home
agent node having received the notification transfers IP packets,
which are destined for the moved mobile station and received
thereafter from the IP network, to the specific packet node.
5. The mobile IP network system according to claim 1, wherein each
of said packet nodes has a foreign agent function for transferring
an IP packet received from the home agent node connected to the IP
network to any of the base station controllers.
6. A method of switching a connection for communication between a
mobile station connected to any of a plurality of radio access
networks via a radio link and a plurality of packet nodes connected
to an IP network, comprising: a step of connecting between a mobile
station connected to a first radio access network and a first
packet node which is preliminarily related with the first radio
access network; a step of transferring, by said first packet node,
IP packets for the mobile station which are received from a home
agent node of the mobile station, to the first radio access network
using an identifier of the first logical connection; a step of
connecting the mobile station to a second radio access network
adjacent to the first radio access network when the mobile station
moves into an area of the second radio access network; and a step
of requesting from the second radio access network to the first
packet node to communicate IP packets for the mobile station with
the second radio access network while the mobile station connected
to the first packet node, wherein IP packets are communicated
between the mobile station and the first packet node without
performing a registration procedure between the mobile station and
said home agent node until communication of IP packets for the
mobile station is ceased.
7. The switching method according to claim 6, further comprising: a
step of closing, upon detecting that data transmission and
reception ceased, the connection between the mobile node and the
first packet node and beginning the connection between the mobile
node and the second packet, said second packet node being
preliminarily related with the second radio access network.
8. A base station controller for a radio access network for
transmitting and receiving an IP packet to and from a packet node
which is connected to an IP network and has a foreign agent
function for transferring IP packets from a home agent node to
mobile stations, comprising: a first communication interface for
connection to a radio base station, a second communication
interface for communication with a plurality of packet nodes
connected to the IP network, and a control unit connected to the
first and second communication interfaces, wherein the control unit
selectively begins an IP packet communication between the base
station and the packet node or to transfer IP packets for the
mobile station to the mobile station connected to another radio
access network, via the second interface; wherein said control unit
has means for selecting, when the mobile station has moved into the
control area of the base station controller from said another radio
access network, a first packet node which is communicating with the
mobile station in the another radio access network, to request the
first packet node to transfer IP packets for the mobile station to
the base station controller; means for monitoring communication
packets for the mobile station which is communicating with said
first packet node; and means for switching a first connection
between the mobile station and the first packet node to a second
connection between the mobile station and a second packet node
preliminarily related to the base station controller when it is
detected by the monitoring means that the transmission of
communication packets for the mobile station is stopped, wherein
said connection is established after performing a registration
procedure between the moved mobile station and said home agent
node.
9. The base station controller according to claim 8, wherein said
control unit has means for notifying the base station controller in
adjacent one of the other radio access networks of identification
information of a previous packet node which has been communicating
with the mobile station when the mobile station moved out from the
control area of the base station controller to a control area of
the adjacent radio access network.
10. The base station controller according to claim 8, wherein said
second communication interface is connected to a communication
network for connecting the plurality of packet nodes, and said
switching means closes the first connection by requesting said
first packet node to communicate IP packets for the moved mobile
station with the base station controller and establishes said
second connection by requesting said second packet node to
communicate IP packets for the moved mobile station with the base
station controller, when said monitoring means detects that the
transmission of communication packets has stopped.
Description
[0001] The present application is a continuation of application
Ser. No. 09/624,072, filed Jul. 24, 2000, the contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a mobile IP network system
and a connection switching method. More particularly, the invention
relates to a technique of switching a logical connection for IP
packet communications between a radio access network and a packet
node connected to an IP (Internet Protocol) network in association
with movement of a mobile station.
DESCRIPTION OF THE RELATED ART
[0003] In order to enable IP data to be transferred between a
mobile station and a host connected to an IP network typified by
the Internet, a network system in which a mobile communication
network is connected to the IP network via a packet node having a
foreign agent function in a mobile IP is being examined.
[0004] The mobile IP denotes a technique for enabling the
communication between a mobile station and a host to be continued
without changing an IP address even when the connection position
between the mobile station and the IP network changes. In the
mobile IP, a node having a home agent function for each of mobile
stations is preliminarily determined. The home agent function
denotes a function of grasping the current position of mobile
stations under the control, when an IP packet destined for a mobile
station under the control is received, converting the reception
packet to an encapsulated packet destined for a packet node
connected to a radio access network in which the mobile station is
positioned at present, and transmitting the encapsulated packet to
the IP network.
[0005] Each of packet nodes for receiving the encapsulated packet
via the IP network has a foreign agent function. The foreign agent
function denotes here a function of decapsulating the reception
packet and transmitting the obtained IP packet to a radio access
network in which a destination mobile station is positioned.
[0006] By the home agent function and the foreign agent function,
even when a mobile station moves between radio access networks, an
IP packet can be delivered to the mobile station without changing
the IP address of a transmission packet.
[0007] In the following, a node having the home agent function will
be called a home agent node and a node having the foreign agent
function will be called a foreign agent node.
[0008] A communication between a mobile station and a host
connected to an IP network is realized by switching a logical
connection between the mobile station and a foreign agent node by
using a position control function peculiar to a mobile
communication network and routing an IP packet between the foreign
agent node and the host by the mobile IP function.
[0009] The mobile IP is standardized by IETF and is described in,
for example, "IP Mobility Support", C. Perkins, RFC2002, October
1996. A mobile IP data communication in IMT-2000 as a
third-generation mobile communication network is described in
"Wireless IP Network Architecture based on IETF Protocols", Tom
Hiller, 1999 disclosed by TIA as a standardization organization in
North America.
[0010] In the mobile IP, when a mobile station is moved from a
control area of a packet node (foreign agent node) to a control
area of another packet node, a registration procedure for switching
the foreign agent node is necessary in the home agent node.
[0011] The mobile station notifies the home agent node of a
destination packet node and the home agent node registers the
destination packet node as a new foreign agent for the mobile
station. Consequently, the home agent node can transfer an IP
packet destined for the mobile station received after that to the
new foreign agent (packet node on the destination side).
[0012] The conventional technique has a problem such that it takes
time from the request of the registration procedure to the
response. Specifically, when a mobile station moves to a control
area of another packet node and is handed over to a radio base
station in the control area, until the registration is completed in
the home agent node, IP packets destined for the mobile station are
transferred from the home agent node to a packet node in the
previous control area, so that the IP packets are not transferred
to the mobile station. Although the dropped IP packets may be
compensated by retransmission of the IP packets from the host in
response to a request from the mobile station, when the amount of
the dropped IP packets is large, a problem such that the
retransmission of the IP packets severely deteriorates the
throughput occurs.
SUMMARY OF THE INVENTION
[0013] It is an object of the invention to provide a mobile IP
network system and a connection switching method in which dropout
of an IP packet which occurs during a registration procedure of a
destination packet node is prevented.
[0014] In order to achieve the object, the present invention is
characterized in that each of base station controllers in a radio
access network selectively establishes a logical connection or a
logical link with a plurality of packet nodes each having a foreign
agent function.
[0015] More specifically, a mobile IP network system of the
invention comprises: a plurality of radio access networks each
connected to a mobile station via a radio link; and an IP network
to which a plurality of packet nodes for transferring an IP packet
are connected, and is characterized in that a base station
controller in each of the radio access networks is connected to the
plurality of packet nodes, and each of the base station controllers
selects one of the plurality of packet nodes in accordance with a
state of each mobile station, and sets a logical connection to be
used in IP packet communication of the mobile station.
[0016] In the network system according to the invention, when a
mobile station is moved from a control area of another radio access
network to the control area of one of the base station controllers,
the base station controller can sets a logical connection for the
mobile station with a previous packet node which has communicated
with the mobile station in the control area of the another radio
access network. That is, according to the invention, when a mobile
station is moved from a radio access network to another radio
access network, the IP packet communication can be continued
without performing a registration procedure for switching a foreign
agent node. Thus, the problem of the dropout of IP packets in
association with the registration procedure can be solved.
[0017] Another characteristic of a mobile IP network system
according to the invention is that each of the base station
controllers has means for monitoring a transmitting and receiving
state of data to and from a mobile station which has moved from the
control area of another radio access network, detects that data
transmission and reception of the mobile station is stopped,
cancels the logical connection between the base station controller
and the previous packet node, and sets a new logical connection for
the mobile station between the base station controller and a
preliminarily designated specific packet node.
[0018] When the packet node to be connected to the base station
controller via the logical connection is switched, the registration
procedure by the home agent node is necessary. According to the
invention, however, since the registration procedure is performed
during the data transmission and reception of the mobile terminal
is stopped, the problem of the dropout does not occur.
[0019] The foregoing and other objects, advantages, manner of the
operation and novel features of the present invention will be
understood from the following detailed description when read in
conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a diagram schematically showing the construction
of a conventional mobile IP network system.
[0021] FIG. 2 is a diagram specifically showing a radio access
network 2.
[0022] FIG. 3 is a diagram showing schematic constructions of a
mobile station 1, a radio access network 2, a packet node 3, and a
home agent node 5 in FIG. 1.
[0023] FIG. 4 is a diagram showing schematic constructions of base
stations 6 and base station controllers 7 constructing the radio
access network 2.
[0024] FIG. 5 is a diagram showing a schematic construction of a
control unit 31 in the packet node 3.
[0025] FIG. 6 is a diagram for explaining the flow of communication
data between the mobile station 1 and the host 4 in the
conventional mobile IP network system.
[0026] FIG. 7 is a diagram showing a registration procedure
sequence in the conventional mobile IP network system.
[0027] FIG. 8 is a diagram for explaining a change in a transfer
route of an IP packet in the conventional mobile IP network
system.
[0028] FIG. 9 is a processing sequence for changing a transfer
route of an IP packet in the conventional mobile IP network
system.
[0029] FIG. 10 is a diagram showing an example of the construction
of a mobile IP network system according to the invention.
[0030] FIGS. 11A, 11B and 11C are diagrams showing formats of a
transmission packet from a host to a mobile station, a transfer
packet from a home agent node to a packet node, and a transfer
packet from the packet node to a base station controller,
respectively.
[0031] FIG. 12 is a diagram showing a processing sequence for
changing a transfer route of an IP packet in a mobile IP network
system of the invention.
[0032] FIG. 13 is a block diagram showing schematic constructions
of a mobile station 1, a radio access network 2, a packet node 3
and a home agent node 5 constructing a mobile IP network system of
the invention.
[0033] FIG. 14 is a diagram specifically showing the radio access
network 2 in the invention.
[0034] FIG. 15 is a diagram showing the construction of a control
unit 71 in a radio access network of the invention.
[0035] FIG. 16 is a diagram showing the construction of a link
management table 203-3 in FIG. 15.
[0036] FIG. 17 is a flowchart showing an example of processing
operations of a logical link changing unit 203-2 in FIG. 15.
[0037] FIG. 18 is a flowchart showing another example of processing
operations of the logical link changing unit 203-2 in FIG. 15.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] First, for easier understanding of the present invention, a
conventional mobile IP network system will be described with
reference to FIGS. 1 to 9.
[0039] FIG. 1 shows a general construction of the conventional
mobile IP network system.
[0040] The mobile IP network system comprises: a mobile station 1;
a plurality of radio access networks 2 (2A, 2B, . . . ); packet
nodes 3 (3A, 3B, . . . ) each for connecting each of the radio
access networks to an IP network 102; a home agent node 5 of the
mobile station 1; and a host (or server) for performing
communications with the mobile station. The mobile station 1 and
the radio access network 2 are connected via, for example, a radio
link 100 using CDMA. The radio access network 2 and the packet node
3 are connected via a dedicated line 101. The host 4 and the home
agent node 5 are connected to the IP network 102, and each of the
packet nodes 3 has a foreign agent function in a mobile IP.
[0041] Each of the radio access networks 2 (2A, 2B, . . . )
comprises, for example as shown in FIG. 2, one or more base station
controllers 7 (7A, 7B, . . . ) connected to the packet node 3 and
one or more radio base stations 6 each connected to any of the base
station controllers via a dedicated line 103. The packet node 3 and
the base station controllers 7 have the connecting relation of 1 to
m, and the base station controller 7 and the base stations 6 have
the connecting relation of 1 to n. The functions of the base
station controller 7 and the base station 6 may be collected in a
single device called a radio access point.
[0042] FIG. 3 shows schematic constructions of the mobile station
1, radio access network 2, packet node 3 and home agent node 5.
[0043] The mobile station 1 comprises: a man-machine interface
(MMI) 12 including an external device interface function; a radio
frequency unit (RF unit) 13 for communicating with the radio access
network 2 through a radio channel; and a control unit 11 connected
to those elements.
[0044] The radio access network 2 comprises: a radio frequency unit
(RF unit) 22 for communicating with the mobile station 1 via a
radio channel; a dedicated line interface (dedicated line control
unit) 23 for communicating with the packet node 3; and a control
unit 21 connected to those elements.
[0045] The packet node 3 comprises: one or more dedicated line
interfaces 32 for communicating with the radio access network 2; an
IP network interface 33 for a connection to an IP network; and a
control unit 31 connected to those elements.
[0046] The home agent node 5 comprises an IP network interface 52
for a connection to the IP network and a control unit 51.
[0047] FIG. 4 shows an example of a specific construction of the
radio access network 2.
[0048] The radio access network 2 comprises the one or more base
station controllers 7 (7A, 7B, . . . ) and the plurality of base
stations 6 (6A, 6B, 6C, . . . ) each connected to any of the base
station controllers.
[0049] Each base station 6 comprises an RF unit 62 for
communicating with the mobile station 1 via a radio channel; a
dedicated line interface (dedicated line control unit) 63 for
communicating with the base station controller 7; and a control
unit 61 connected to those elements.
[0050] Each of the base station controllers 7 comprises one or more
dedicated interfaces (dedicated line control units) 72 for
communicating with the base station 6; a dedicated line interface
(dedicated line control unit) 73 for communicating with the packet
node 3; and a control unit 71 connected to those elements.
[0051] The RF unit 22 in the radio access network shown in FIG. 3
corresponds to the RF unit 62 in the base station 6, the dedicated
line interface 23 corresponds to the dedicated line interface 73 in
the base station control unit 7, and the control unit 21
corresponds to a combination of the control unit 61 in the base
station and the control unit 71 in the base station controller.
[0052] FIG. 5 shows the construction of the control unit 31 in the
packet node 3.
[0053] In the control unit 31, an OS 202 operates on hardware 201
comprising a CPU and a memory, and AP (application software) 203
which determines the behavior of a packet node operates under the
control of the OS 202. Each of the control units in the mobile
station 1, base station 6, base station controller 7 and home agent
node 5 has basically the construction similar to that of the
control unit 31.
[0054] FIG. 6 shows the flow of communication data between the
mobile station 1 and the host 4 in the conventional mobile IP
network system.
[0055] The host 4 generates an IP packet including transmission
data to the mobile station 1 and an IP address of the mobile
station 1 and transmits the IP packet to the IP network 102. The IP
packet is received by the home agent node 5 of the mobile station
1.
[0056] The home agent node 5 stores the corresponding relation
between an IP address of each of mobile stations under the control
and an IP address of each of packet nodes connected to the radio
access network as a destination. The home agent node 5 obtains the
IP address of the packet node 3A to which the reception packet is
transferred on the basis of the IP address of the mobile station
included in the reception packet from the host 4, adds
(encapsulates) a new header in which the IP address of the packet
node 3A is set as a destination address to the reception packet,
and transmits the resultant to the IP network 102.
[0057] Each of the packet nodes 3 stores the corresponding relation
between the IP address of each of the mobile stations connected to
the radio access network under the control and an ID of a logical
connection (Point to Point Protocol (PPP) connection) between the
mobile station and the packet node itself. The packet node 3A
removes or decapsulates the IP header from the encapsulated packet
received from the home agent node 5, obtains a PPP connection ID
corresponding to the mobile station on the basis of the IP address
of the mobile station 1 included in the original IP packet
received, adds the PPP connection ID to the original IP packet, and
transmits the resultant packet to the radio access network 2A under
the control. The packet transmitted from the packet node 3A is
transferred in the radio access network 2A in accordance with the
PPP connection ID and is transmitted from the base station to the
mobile station 1 as a destination.
[0058] The transmission data from the mobile station 1 to the host
4 is transmitted to the packet node 3A via the PPP connection
between the mobile station 1 and the packet node 3A as an IP packet
including the IP address of the host 4 as a destination address.
The IP packet is transferred to the IP network 102 by the packet
node 3A and is received by the host 4.
[0059] FIG. 7 shows a sequence of a registration procedure in the
conventional mobile IP network system.
[0060] In order to realize an IP packet transfer by the
above-described mobile IP, it is necessary to register in the home
agent node a packet node, between which and the mobile station the
logical connection (PPP connection) is established, as a foreign
agent node.
[0061] When a radio link is established between the mobile station
1 and the base station 6C in the area in which the mobile station 1
is positioned by the base station controller 7B in the radio access
network 2A (step 401), a request for starting packet service
(transmission and reception of packets) is sent from the base
station controller 7B in the radio access network 2A to the packet
node 3A (402), and a logical connection (PPP connection) is
established between the packet node 3A and the mobile station 1
(403).
[0062] After the PPP connection is established, the packet node 3A
notifies the mobile station 1 of the IP address of the packet node
itself via the PPP connection (advertisement:404). The mobile
station 1 which has received the advertisement requests the packet
node 3A for registration (405), and the packet node 3A transfers
the registration request to the home agent node 5 of the mobile
station 1 (406). The home agent node 5 which has received the
registration request from the mobile station 1 registers the packet
node 3A as a foreign agent corresponding to the mobile station 1
and then sends a registration response to the packet node 3A
(407).
[0063] When the packet node 3A transfers the registration response
to the mobile station 1 (408), the registration procedure is
completed. By the procedure, the IP packet transmitted from the
host 4 to the mobile station 1 is transferred from the home agent
node 5 to the packet node 3A registered as a foreign agent, so that
it can be transferred to the mobile station 1 via the PPP
connection established between the packet node 3A and the mobile
station 1 (409).
[0064] FIG. 8 shows a change in the IP packet transfer route in the
conventional IP network system in association with a movement of
the mobile station.
[0065] For example, when the mobile station 1 moves from the radio
access network 2A as a control area of the packet node 3A to the
radio access network 2B as a control area of the packet node 3B, as
a result of hand-over between the base stations, the radio link
established between the base station 6C in the radio access network
2A and the mobile station 1 and the logical connection (PPP
connection) established between the mobile station 1 and the packet
node 3A are released. In stead, a radio link between the base
station 6D in the radio access network 2B and the mobile station 1
and a logical connection (PPP connection) between the mobile
station 1 and the packet node 3B are established.
[0066] A registration procedure is executed in the radio access
network 2B as a destination and the packet node 3B is registered as
a new foreign agent of the mobile station 1. Consequently, the IP
packet transmitted from the host 4 to the mobile station 1 is
transferred from the home agent node 5 to the packet node 3B and is
transferred from the packet node 3B to the mobile station 1 via the
PPP connection as shown by arrows with solid lines.
[0067] FIG. 9 shows a processing sequence for changing the IP
packet transfer route in the conventional mobile IP network
system.
[0068] When the mobile station 1 moves toward the control area of
the radio access network 2B while performing communication with the
host via the PPP connection with the packet node 3A (409), the
mobile station 1 compares the reception strength of a control
signal received from the base station 6C in the radio access
network 2A shown in FIG. 8 with that of a control signal received
from the base station 6D in the radio access network 2B. At a time
point the reception strength from the base station 6D becomes
stronger, a request of handover to the base station 6D is issued
(501).
[0069] The handover request is notified from the base station
controller 7B in the radio access network 2A to the base station
controller 7C in the radio access network 2B via a control circuit
connecting these base station controllers (502). If the base
station 6D can accommodate the mobile station 1, the base station
controller 7C returns a handover response to the base station
controller 7B (503). When the base station controller 7B which has
received the handover response instructs the handover to the mobile
station 1 (504), the base station 6D as a destination allocates a
radio channel to the mobile station 1, and a new radio link is
established between the mobile station 1 and the radio access
network 2B (505).
[0070] The base station controller 7C in the radio access network
2B establishes the logical connection between the mobile station 1
and the packet node 3B and requests to start transmission and
reception of packets to and from the mobile station 1 (506). In
parallel with this, the base station controller 7B in the radio
access network 2A closes the logical connection established between
the mobile station 1 and the packet node 3A (507). The packet node
3B which has received the request from the base station controller
7C establishes a logical connection (PPP connection) with the
mobile station (508) and notifies the IP address of the packet node
to the mobile station 1 (advertisement: 509).
[0071] In response to reception of the advertisement, the mobile
station 1 requests a registration of a foreign agent to the packet
node 3B (510) and the packet node 3B transfers the registration
request to the home agent node 5 (511). After registering the
packet node 3B as a new foreign agent of the mobile station 1, the
home agent node 5 transmits a registration response to the packet
node 3B (512). When the registration response is transferred from
the packet node 3B to the mobile station 1 (513), it is able to
perform a packet communication via the PPP connection between the
mobile station 1 and the packet node 3B (514).
[0072] As described above, in the conventional mobile IP network
system, when a mobile station moves to the control area of another
radio access network, in association with a handover of the mobile
station between the base stations, the registration procedure for
switching the foreign agent is executed. In this case, during a
period (T1) since the mobile station is handed over to the
destination radio access network until switching of the lo foreign
agent is completed, the home agent node 5 keeps on transferring the
IP packets destined to the mobile station 1 to the previous packet
node 3A. The mobile station 1 cannot therefore receive the IP
packets transmitted from the host during the period T1, so that a
considerable amount of IP packets are dropped out.
[0073] With reference to FIGS. 10 to 18, the construction of the
mobile IP network system according to the invention and the method
of switching the connection will be described.
[0074] FIG. 10 shows an example of the construction of a mobile IP
network system according to the invention.
[0075] The invention is characterized in that the plurality of
packet nodes 3 (3A, 3B, . . . ) having the foreign agent function
which are connected to the IP network 102 and the base station
controllers 7 (7A, 7B, 7C, . . . ) in the radio access networks 2
are connected via a network 104 such as an ATM network.
[0076] In the conventional mobile IP network system, the packet
node 3 and the base station controllers 7 have the connecting
relation of 1 to m via the dedicated lines 101, and each of the
base station controllers can communicate with the IP network only
via a specific packet node coupled via a dedicated line. On the
contrary, in the mobile IP network system of the invention, the
packet nodes 3 and the base station controllers 7 have the
connecting relation of k to m (k, m.gtoreq.2) via the network 104.
A logical connection can be selectively established between each of
the base station controllers 7 and any of the packet nodes 3.
[0077] The present invention is characterized in that, for example,
when the mobile station 1 which is performing the IP packet
communication via the packet node 3A moves from the radio access
network 2A to the radio access network 2B and is handed over from
the base station 6C to the base station 6D, the base station
controller 7C in the destination establishes a logical connection
with the previous packet node 3A so that the mobile station 1 can
continue the IP packet communication via the packet node 3A.
[0078] In the mobile IP network system, for example, as shown in
FIG. 11A, the host 4 generates an IP packet PA in which an IP
header including an IP address 601 of a destination mobile station
is added to transmission data 600 destined for the mobile station 1
and transmits the IP packet PA to the home agent node 5 of the
destination mobile station. A packet is transferred from the host 4
to the home agent node 5 in the form of, for example, an
encapsulated packet obtained by adding the IP address of the home
agent node as a destination IP address to the IP packet PA.
[0079] The home agent node 5 has a management table in which the IP
address of a packet node in the radio access network in which each
of the mobile stations is positioned at present is stored in
correspondence with the IP address of a mobile station under the
control. When a packet from the host 4 is received, the home agent
node 5 refers to the management table on the basis of the IP
address 601 of the destination mobile station included in the
reception packet PA and retrieves the IP address of the packet node
3A to which the reception packet is transferred. The home agent
node 5 adds an IP header including an IP address 602 of the packet
node 3A as a destination address to the received IP packet PA and
transmits the resultant as an encapsulated packet PB shown in FIG.
11B to the IP network 102.
[0080] The packet node has a management table in which the
corresponding relations among the IP address of the mobile station
which is performing communication via the PPP connection, the PPP
connection ID, and the IP address of the base station controller
related to the PPP connection. When a packet is received from the
home agent node 5, the packet node decapsulates the reception
packet PB, refers to the management table on the basis of the
destination mobile station IP address 601 in the obtained IP packet
PA, and retrieves the corresponding PPP connection ID and the IP
address of the base station controller (BSC). The packet node 3A
adds a header including a PPP connection ID 603 and an IP address
604 of the base station controller 7B as a destination address to
the reception IP packet PA and transmits the resultant in the form
of a packet PC shown in FIG. 11C to the network 104. When the
network 104 is an ATM network, the packet PC is converted to a
plurality of ATM cells to each of which a cell header including an
ID (VPI/VCI) of the logical connection between the packet node 3A
and the base station controller 7B is added and the resultant is
transmitted to the network 104.
[0081] The base station controller 7B eliminates the IP address 604
from the reception packet PC and transfers the resultant packet to
the base station 6C specified by the PPP connection ID 603. The
base station 6C transfers the reception packet to the mobile
station 1 via a radio link specified by the PPP connection ID 603.
The mobile station 1 checks the destination IP address 601 of the
reception packet and performs a process of receiving the IP packet
destined to itself.
[0082] FIG. 12 shows a processing sequence for changing the
transfer route of the IP packet in the mobile IP network system of
the invention. In FIG. 12, in order to make comparison with the
conventional processing sequence described in FIG. 9 easier, the
corresponding steps are designated by the same reference numerals.
In the following, on the precondition that the mobile IP network
system of FIG. 10 is used, description of the above sequence will
be omitted here but the processing sequence for changing the IP
packet transfer route in the invention will be described.
[0083] When the mobile station 1 which is PPP connected to the
packet node 3A is moved to the control area of the radio access
network 2B, a handover request is sent from the mobile station 1 to
the base station controller 7B in the radio access network 2A
(501), and a radio channel of the radio access network 2B is
allocated to the mobile station 1 via handover procedures 502, 503
and 504 similar to the conventional handover procedures (505).
[0084] In the present invention, when the base station controller
7B in the radio access network 2A which has received the handover
request (501) from the mobile station 1 notifies the handover
request to the base station controller 7C in the radio access
network 2B, the ID of the packet node 3A to which the mobile
station 1 is presently PPP connected is also notified to the base
station controller 7C (502).
[0085] The base station 6C itself may send the handover request
(501) with respect to the mobile station 1 to the base station
controller 7B when the base station 6C detects that the strength of
the received radio wave from the mobile station 1 which is
performing communications drops below a predetermined level. It is
also possible that the mobile station 1 issues a handover request
to the base station controller 7C via the destination base station
6D and the base station controller 7C instructs handover to the
mobile station 1. In this case, the base station controller 7C has
to be notified of the ID of the base station controller 7B, which
is being connected from the mobile station 1, to inquire the base
station controller 7B of the ID of the packet node which is PPP
connected to the mobile station 1.
[0086] When a radio link is established between the mobile station
1 and the destination base station 6D (505), in the conventional
system, the base station controller 7C connected to the base
station 6D sends a request of the packet transmission and reception
to and from the mobile station 1 to the specific packet node 3B
preliminarily designated (506) and a new logical connection (PPP
connection) to communication with the mobile station 1 is
established (508). In contrast, in the invention, the base station
controller 7C sends the request of packet transmission and
reception to and from the mobile station 1 to the previous packet
node 3A to which the mobile station 1 is PPP connected at the time
of handover (701). The packet node 3A changes the destination
address 604 to the IP address of the base station controller 7C as
a request source in a state where the PPP connection to the mobile
station 1 is maintained, and transfers the IP packet destined to
the mobile station 1 to the base station controller 7C. When an ATM
network is used as the network 104, a preset PVC (Permanent Virtual
Connection) can be used for the packet communication between the
base station controller and the packet node.
[0087] In parallel with the operation of the base station
controller 7C, the base station controller 7B closes the logical
connection for the mobile station 1 between the base station
controller 7B and the packet node 3A (702). In this case, since the
connecting relation between the mobile station 1 and the packet
node 3A is unchanged, the registration procedure of the foreign
agent node is unnecessary and communication interruption time T2 in
the destination radio access network 2B is extremely short.
[0088] In the invention, each of the base station controllers
monitors a transmitting and receiving state of the IP packet for
each mobile station under control, confirms that the transmission
and reception of the IP packet to and from the mobile station is
ceased, and executes the registration procedure. For example, the
base station controller 7C is provided with a data flow monitoring
timer for repeating measurement of elapsed time each time the IP
packet is transmitted and received to and from the mobile station
1. When the data flow timer times out, it is determined that the
transmission and reception of the IP packet is ceased. A request of
starting packet service (packet transmission and reception) is sent
to a specific packet node (in this example, the packet node 3B)
which is preliminarily designated for each base station controller
(506) and the logical connection related to the mobile station 1
with the packet node 3A which has been performing communications is
closed (704). By the operation, the logical connection (PPP
connection) between the mobile station 1 and the packet node 3B is
established (508) and a registration is executed by a procedure
(509 to 513) similar to the conventional one.
[0089] In order to shorten the time required for the registration,
for example, it is also possible that, at the time point a handover
request is received (502), the base station controller 7C requests
the specific packet node 3B to set a temporary logical connection
and, when the data flow monitoring timer times out, an
advertisement request is issued to the mobile station 1. It is also
possible to restart the data flow monitoring timer by the base
station controller 7C after completion of the registration
procedure and, when the timer times out again, a dormant processing
(705) for releasing the radio channel allocated to the mobile
station 1 may be executed in order to effectively use the radio
channel.
[0090] FIG. 13 shows schematic constructions of the mobile station
1, radio access network 2, packet node 3 and home agent node 5
which construct the mobile IP network system of the invention.
[0091] The difference from the conventional system shown in FIG. 3
is that the radio access network 2 and the packet node 3 have
interfaces (IP network interfaces: ATM network interfaces) 24 and
34 for connection to the common network 104 in place of the
dedicated line interfaces 23 and 32.
[0092] FIG. 14 specifically shows the construction of the radio
access network 2.
[0093] Each of the base station controllers 7 (7A and 7B) in the
radio access network 2 has a line interface (IP network interface:
ATM network interface) 74 for connection to the common network 104
in place of the dedicated line interface 73 for communicating with
the packet node 3. The common network 104 is an IP network such as
an ATM network and includes IP nodes (ATM switches) 8A, 8B, 8C, . .
. for accommodating the plurality of base station controllers 7 and
the plurality of packet nodes 3.
[0094] FIG. 15 shows an embodiment of the control unit 71 in the
base station controller in each of the radio access networks.
[0095] The control unit 71 in the base station controller
comprises: hardware 201 such as a CPU and a memory, a real-time OS
202, and an application 203 which operates under the control of the
OS. The application has not only a radio resource management unit
203-1 but also, for each of the mobile stations under the control,
a data flow monitor 203-4 for monitoring the flow of transmission
and reception data, a data flow monitoring timer 203-5 for
measuring time in which the data transmission and reception to and
from each of the mobile stations is ceased on the basis of the
result of the monitoring of the data flow monitor, a timer
information table 203-6 for storing data such as a time-out value
required by the data flow monitoring timer, a link management table
203-3 for memorizing a packet node which is PPP connected at
present for each mobile station under the control, and a logical
connection changing unit 203-2 for controlling the switching of the
logical connection (PPP connection) on the basis of the link
management table.
[0096] The link management table 203-3 stores, for example as shown
in FIG. 16, the relations among an ID 301 of a mobile station under
the control of the base station controller 7, an ID 302 of a packet
node to which the mobile station is PPP connected at present, and
an ID 303 of a preliminarily designated specific packet node. As
the ID 303 of the specific packet node, a packet node having the
shortest connecting path with the base station controller 7 is
registered.
[0097] FIG. 17 shows processes of the logical link changing unit
203-2 executed by the control unit 71 in the base station
controller 7 when the data flow monitoring timer 203-5 times
out.
[0098] When the data transmission and reception of a certain mobile
station is stopped for predetermined time or longer and the data
flow monitoring timer 203-5 times out, the logical link changing
unit 203-2 refers to the link management table 203-3 and compares
the packet node 302 in connection and the designated packet node
303, corresponding to the mobile station, thereby determining
whether or not the mobile station is PPP connected to the
preliminarily designated specific packet node (step 801).
[0099] In the case where the mobile station is PPP connected to the
preliminarily designated packet node, the routine advances to a
dormant mode and the radio channel allocated to the mobile station
is released (802). The data flow monitoring timer is started again
and the process is terminated (804). If the mobile station is PPP
connected to a packet node except for the designated packet node, a
request for starting the transmission and reception of packets to
and from the mobile station is issued to the designated packet node
in order to PPP connect the mobile station to the designated packet
node. After the ID of the designated packet node is registered in
the packet node in connection field 302 (803), the data flow
monitoring timer is started again and the process is terminated
(804).
[0100] FIG. 18 shows the processing operation of the logical link
changing unit 203-2 in the base station controller 7 in the radio
access network 2 which does not have the dormant processing
function.
[0101] The logical link changing unit 203-2 waits for a time-out
signal from the data flow monitor 203-4 (901). When the time-out
signal is received, that is, it is detected that the data
transmission and reception of a certain mobile station is ceased
for predetermined time or longer, it is determined, by referring to
the link management table 203-3, whether or not the mobile station
is PPP connected to the specific packet node preliminarily
designated in the self base station controller (902).
[0102] When the mobile station is PPP connected to the designated
packet node, measurement of the data flow is started again (904).
When the mobile station is PPP connected to a packet node other
than the designated packet node, in order to PPP connect the mobile
station to the designated packet node, a request for starting the
transmission and reception of a packet to and from the mobile
station is sent to the designated packet node and the ID of the
designated packet node is registered in the field 302 of the packet
node in connection (903). After that, the measurement of the data
flow is started again (904).
[0103] As obviously understood from the embodiment, the invention
is characterized in that the plurality of packet nodes 3 connected
to the IP network 102 and a plurality of base station controllers 7
in the radio access network 2 are connected to each other via the
network 104, and each of the base station controllers can
selectively connect the mobile station handed over from another
radio access network to any of the packet nodes.
[0104] In the embodiment shown in FIG. 10, the network 104 for
connecting the packet node 3 and the base station controller to
each other and the IP network 102 to which the home agent node is
connected are separate networks. In order to achieve the object of
the invention, however, the network 104 may be a part of the IP
network 102. That is, the following manner may be also used in
which each of the base station controllers 7 is connected to the IP
network 102 and, for example, the packet node 3A transfers an IP
packet, which is transferred from the home agent 5 to the packet
node 3A via the IP network 102, to the base station controller 7B
or 7C via the IP network 102.
[0105] As obviously understood from the foregoing embodiment,
according to the invention, a logical connection can be selectively
established between each of the base station controllers in the
radio access network and an arbitrary packet node having the
foreign agent function. Consequently, when a mobile station is
handed over from one radio access network to another radio access
network, without switching the foreign agent node in the
destination radio access network, the mobile station can be
logically connected to the previous packet node and the IP packet
communication can be continued. The mobile IP packet communication
which avoids dropout of packets during execution of the
registration for switching the foreign agent node can be therefore
performed.
[0106] According to the invention, since the registration of the
foreign agent node is executed during the period in which the IP
packet transmission and reception is ceased, even when the foreign
agent node is switched to the optimum packet terminal in
association with the movement of the mobile station, dropout of
packets during the registration period can be avoided.
* * * * *