Mobile communication system and access gateway having plural user plane AGWs

In an access gateway (AGW) comprising a C-AGW for handling control messages and a plurality of U-AGWs for handling data packets, when a tunnel setup request is issued from one of base stations to hand over a mobile station, the C-AGW selects a new U-AGW being in the lowest load status out of the U-AGWs, estimates the load status of the new U-AGW in the case of changing the tunnel endpoint for the mobile station from a current U-AGW to the new U-AGW. The C-AGW designates the new U-AGW as the tunnel endpoint for the mobile station if the estimated load status satisfies a predetermined condition, but designates the current U-AGW as the tunnel endpoint if the estimated load status does not satisfy the predetermined condition.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent application serial No. 2009-030974, filed on Feb. 13, 2009, the content of which is hereby incorporated by reference into this application.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a mobile communication system and, more particularly, to a mobile communication system including an Access Gateway (AGW) located between a core network and an access network accommodating a plurality of base stations.

(2) Description of Related Art

In a wireless access network, a tunnel is established between a Base Station (BS) and an Access Gateway (AGW) and control messages and user data are transmitted through the tunnel, using a mobile IP (Mobile Internet Protocol) of the IETF (Internet Engineering Task Force). The tunnel of mobile IP is established by exchanging, for example, a Registration Request (RRQ) message and a Registration Reply (RRP) message of Proxy Mobile IP (PMIP) between the BS and the AGW. The formats of RRQ message and RRP message of PMIP are disclosed in IETF RFC3344, sections 3.1 and 3.2.

Meanwhile, in a wireless access network such as UMB (Ultra Mobile Broadband)/CAN (Converged Access Network) of 3rd Generation Partnership Project 2 (3GPP2), separation between a control plane for handling control messages and a user plane for handling user data is pursued. For example, 3GPP2 X. S0054-100-0 v1.0, sections 4.4 and 4.6, disclose that a data path and a signaling path are separated at an AGW.

FIG. 3shows an example of a conventional wireless access network. A home agent (HA)2of mobile IP and an Authentication Authorization and Accounting (AAA) server3for performing user authentication, access authorization, and accounting are connected to a core network1. Base stations (BSs)10(10A,10B, . . .10N) are connected to the core network1via an access gateway AGW4. Reference numeral7denotes a session control apparatus (SRNC: Session Reference Network Controller) and reference numerals20(20A,20B, . . . ) denote mobile stations (ATs).

The AGW4includes an AGW unit5for control use which handles control messages (control packets) and an AGW unit6for user data forwarding which handles user data (user packets). In the following description, the AGW unit5for control use is referred to as a C-AGW (Control plane AGW) and the AGW unit6for user data forwarding as a U-AGW (User plane AGW). In the above wireless access network, control packets are forwarded via the C-AGW5as indicated by dotted lines, and user packets are forwarded via the U-AGW6as indicated by solid lines.

FIG. 4shows an example of a signaling sequence to be performed, for example, to establish a tunnel for forwarding user data between a BS10A and the AGW4when an AT20A is connected to the core network1, in the wireless access network shown inFIG. 3.

When a connection request is issued from the AT20A, an access authentication procedure is executed between the AAA server3and the AT20A via the BS10A, SRNC7, and C-AGW5(SQ10a, SQ10b, SQ10c). At this time, the BS10A is notified from the C-AGW5of an IP address of C-AGW5as AGW-ID (SQ11), and the C-AGW5is notified from the AT20A of an identifier (ATID) of AT20A to be authenticated (SQ12).

Upon completion of the access authentication of AT20A, the BS10A performs configurations (SQ14a, SQ14b) to establish a wireless connection between the AT20A and the BS10A. After that, the BS10A transmits to the C-AGW5a tunnel setup request message to establish a tunnel for forwarding user data. The tunnel setup request includes the identifier (ATID) of AT20A. In this example, a PMIP RRQ message is transmitted as the tunnel setup request (S015). In the case of a system configuration that allows the AGW4to establish a plurality of tunnels for the same AT, the BS10A adds control information (“Primary”) for indicating the first tunnel setup to the PMIP RRQ message.

Upon receiving the PMIP RRQ message, the C-AGW5returns a reply message, which is a PMIP RRP message in this example, to the BS10A (SQ16). The PMIP RRP message includes an IP address of U-AGW6as information (“Endpoint”) for indicating a termination point of the tunnel. Upon receiving the PMIP RRP message from the C-AGW5, the BS10A establishes a tunnel toward the U-AGW6specified by the “Endpoint” (SQ18). Thereby, the AT20A transits into a state capable of communicating user data with a correspondent node connected to the core network1through the tunnel established between the BS10A and the U-AGW6(SQ19a, SQ19b, SQ19c).

In the case where the AGW4includes a single U-AGW6as in the wireless access network shown inFIG. 3, the C-AGW5can return a reply message designating the same U-AGW as the Endpoint, in response to every tunnel setup request received from the base stations10A to10N. However, in the case where the AGW4comprises a C-AGW and a plurality of U-AGWs, when a tunnel setup request is received from one of base stations, the C-AGW5has to assign an optimum U-AGW to an AT by taking the load conditions of the U-AGWs into account. 3GPP2 X. S0054-100-0 v1.0 does not disclose about a method of assigning a specific U-AGW to each AT by the AGW4provided with a plurality of U-AGWs.

In a broadband mobile communication system such as UMB (Ultra Mobile Broadband), an elaborate handover control adaptable to mobile ATs is required in order to achieve high-speed data transmission with high efficiency. In the UMB communication system, BS switching control is performed so as to connect an AT to one of BSs for which both the statuses of uplink channel and downlink channel are the best, for example, by monitoring the status of uplink radio channel from the AT to each BS and the status of downlink radio channel from the BS to the AT, by the AT20and BSs10.

In this case, there is a possibility that handovers of the same AT occur frequently between BSs for a short period depending on the situation of radio channels, with the result that ineffectual control procedures are executed repeatedly. If the conditions for AT handover between BSs occur frequently, it becomes difficult for BSs and AGW to follow up these handovers because a certain time is required for the tunnel setup between BS and AGW.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a mobile communication system and an access gateway (AGW) enabling assignment of an optimum U-AGW selected from among a plurality of U-AGWs when a tunnel setup request occurs from a base station.

Another object of the present invention is to provide a mobile communication system and an access gateway (AGW) capable of assigning a U-AGW to a base station originating a tunnel setup request so as to distribute loads to a plurality of U-AGWs when a tunnel set up request is received from the base station.

To achieve the above objects, one aspect of the present invention resides in a mobile communication system comprising a plurality of base stations for communicating in wireless with mobile stations and an access gateway (AGW) connected to a core network, wherein tunnels for forwarding data packets are established between each of the base stations and the AGW. The AGW comprises an access gateway unit (C-AGW) for control use to communicate control messages with each of the plurality of base stations via an access network and a plurality of access gateway units (U-AGWs) for data forwarding, each of which communicates data packets with the plurality of base stations via the access network. The C-AGW comprises: a first management table for indicating load status information of each of the U-AGWs in association with an address of each of the U-AGWs; and a controller that retrieves the address of a new U-AGW being in the lowest load status from the first management table when a tunnel setup request message including a mobile station identifier was received from one of the base stations, and returns to the base station a reply message designating the address of the new U-AGW as a tunnel endpoint, wherein, when the tunnel setup request message has been transmitted from a base station to which a mobile station having the mobile station identifier is to be handed over, the controller estimates the load status of the new U-AGW in the case of changing the tunnel endpoint for the mobile station from a current U-AGW to the new U-AGW and designates, as the tunnel endpoint in the reply message, the address of the new U-AGW if the estimated load status satisfies a predetermined condition, but the address of the current U-AGW if the estimated load status does not satisfy the predetermined condition.

For example, in the case where L1stands for the load of the current U-AGW, L2the load of the new U-AGW, and ΔL a load occupied by the mobile station questing to establish a tunnel, L1and L2are in a relation L1>L2now, because the new U-AGW is in the lowest load status. When the tunnel endpoint is switched from the current U-AGW to the new U-AGW, the load of the current U-AGW changes from L1to L1−ΔL and the load of the new U-AGW changes from L2to L2+ΔL.

Here, L2+ΔL represents the estimated load status of the new U-AGW in the case of switching the tunnel endpoint. If a condition of L1>L2+ΔL is satisfied, a difference between the load of new U-AGW and the load of current U-AGW can be made smaller than the current state by switching the tunnel endpoint from the current U-AGW to the new U-AGW, and a load distribution effect is obtained. However, if L1is equal to or smaller than L2+ΔL, the switching of the tunnel endpoint from the current U-AGW to the new U-AGW makes the difference between the load of new U-AGW and the load of current U-AGW larger than the current state and the tunnel endpoint switching has an adverse effect on load distribution over the U-AGWs.

More specifically, in another aspect of the present invention, the C-AGW of the access gateway further has a second management table including a plurality of table entries, each of which indicates, in association with a mobile station identifier, an address of one of the base stations and an address of one of the U-AGWs to be endpoints of a tunnel, and when a tunnel setup request message was received from one of the base stations, the controller of the C-AGW searches the second management table for an objective table entry indicating the addresses of the base station and the current U-AGW being the endpoints of an existing tunnel corresponding to the mobile station identifier specified in the tunnel setup request message, so that when the objective table entry is not registered in the second management table, the controller registers a new table entry indicating, in association with the mobile station identifier, the address of the base station and the address of the new U-AGW to the second management table and returns the reply message designating the address of the new U-AGW as the tunnel endpoint to the base station, and when the objective table entry has already been registered in the second management table, the controller determines whether the predetermined condition is satisfied or not based on the estimated load status of the new U-AGW and the load status of the current U-AGW indicated in said first management table.

When the estimated load status of the new U-AGW does not satisfy the predetermined condition, the controller of the C-AGW rewrites the base station address in the objective table entry registered in the second management table to the address of the base station having transmitted the tunnel setup request message.

In the case where the tunnel setup request message requests to establish a second tunnel to be coexistent with a first tunnel being used by the mobile station having the mobile station identifier, the controller of the C-AGW registers to the second management table a new table entry indicating, in association with the mobile station identifier specified in the tunnel setup request message, the address of the base station having transmitted the tunnel setup request message and the address of the U-AGW designated as the tunnel endpoint in the reply message.

In one embodiment of the present invention, the C-AGW of the access gateway further has a third management table including a plurality of table entries, each of which indicates, in association with a mobile station identifier, communication quality information to be ensured to a mobile station having the mobile station identifier, and the controller of the C-AGW searches the third management table for communication quality information corresponding to the mobile station identifier specified in the tunnel setup request message and estimates the load status of the new U-AGW in the case of changing the tunnel endpoint, based on the communication quality information and load status information of the new U-AGW indicated in the first management table.

In one embodiment of the present invention, the controller of the C-AGW collects load status information periodically from each of the plurality of U-AGWs and stores the load status information into the first management table. In another embodiment of the present invention, the controller of the C-AGW updates the load status information of each of the U-AGWs stored in the first management table based on the second and third management tables.

According to the present invention, when a tunnel setup request issued from a base station which is a target base station to hand over a mobile station, the C-AGW selects a new U-AGW being in the lowest load status out of the plurality of U-AGWs, estimates the load status of the new U-AGW in the case of switching the tunnel endpoint for the mobile station from the current U-AGW to the new U-AGW, designates the new U-AGW as the tunnel endpoint for the mobile station if the estimated load status satisfies a predetermined condition, but designates the address of the current U-AGW as the tunnel endpoint if the estimated load status does not satisfy the predetermined condition.

According to the present invention, therefore, since the tunnel endpoint switching is avoided if no load distribution effect is expected by the tunnel endpoint switching and the same U-AGW as the endpoint of the existing tunnel having been established by a source base station of the handover can be notified to the target base station as an endpoint of a new tunnel, it becomes possible to forward communication packets for the mobile station via the same U-AGW continuously even when the base station to be connected in wireless to the mobile station has switched to the target base station.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1shows an example of a mobile communication system to which the present invention is applied. In the mobile communication system shown here, an AGW4equipped with a plurality of U-AGWs6(6-1to6-m) is located between an access network8and a core network1. The access network8accommodates a session control apparatus SRNC (Session Reference Network Controller)7and a plurality of base stations10(10A,10B, . . .10N), and the core network1includes a Home Agent (HA)2and an AAA server3. In the AGW4, the plurality of U-AGWs6(6-1to6-m) are connected to a C-AGW5by an AGW internal bus40.

FIG. 2shows logical connection relationships among BSs10, SRNC7, AGW4, HA2, and AAA server3shown inFIG. 1. In the mobile communication system of the present invention, control messages (control packets) are handled by the C-AGW5as indicated by dotted lines, and user data (user packets) are handled in distributive manner by the plurality of U-AGWs6-1to6-mas indicated by solid lines.

In the present embodiment, the C-AGW5is provided with a U-AGW status table for indicating the load status of each U-AGW6, a QoS information table for storing user QoS profile information in association with the identifier ATID of each mobile station (AT) having been authenticated to have an access right, and a U-AGW address table for storing the addresses of a base station (BS) and a U-AGW to be the endpoints of a tunnel in association with ATID, as will be described later. The QoS information table stores as user QoS profile information, for example, QoS information representing priority, maximum bandwidth, etc. to be assured for each AT and other information such as a maximum CPU occupation rate allowed for each AT.

Upon receiving a tunnel setup request message including an AT identifier (ATID) from one of BSs10, the C-AGW5determines whether a table entry including the ATID exists in the U-AGW address table. If the table entry corresponding to the ATID is not registered yet, the C-AGW5determines the load status of each U-AGW by referring to the U-AGW status table, selects the address of an optimum U-AGW to be the tunnel endpoint so that processing load are distributed over the plurality of U-AGWs6-1to6-m, and notifies the U-AGW address to the BS having transmitted the tunnel setup request.

InFIG. 2, user packets to be communicated by an AT20A are forwarded through a tunnel9A established between the BS10A and the U-AGW6-1. User packets to be communicated by an AT20B are forwarded through a tunnel9B established between the BS10B and the U-AGW6-2, and user packets to be communicated by an AT20C are forwarded through a tunnel9C established between the BS10N and the U-AGW6-m.

Now, assume that the AT20A has moved from a coverage area of BS10A into a coverage area of BS10B as indicated by a dotted line box20A, in a state where a table entry for the AT20A has been already registered in the U-AGW address table when establishing the tunnel9A. In the present embodiment, when a tunnel setup request for the AT20A is received from the BS10B, the C-AGW5searches the U-AGW status table for the address of a U-AGW being in the lowest load status and retrieves the address of U-AGW6-1corresponding to the identifier of the AT20A from the U-AGW address table.

If the address of the U-AGW corresponding to the identifier of the AT20A has not been registered in the U-AGW address table, the C-AGW5notifies the BS10B of the address of a new U-AGW, which is in the lowest load status and retrieved from the U-AGW status table, as the tunnel endpoint address. When the U-AGW6-1was selected as the new U-AGW, for example, a new tunnel9A(1) is established between the BS10B and the U-AGW6-2. If a U-AGW6-2was selected as the new U-AGW, a new tunnel9A(2) is established between the BS10B and the U-AGW6-2.

When the U-AGW6-2is selected as the new U-AGW, for example, in the state that the address of the U-AGW6-1corresponding to the identifier of the AT20A has been already registered in the U-AGW address table as in the handover of this example, the C-AGW5refers to the U-AGW status table and estimates transitions of load statuses of the U-AGWs6-1and6-2in the case of switching the endpoint of the tunnel for the AT20A from the current U-AGW6-1to the new U-AGW6-2. The C-AGW5notifies the BS10B of the address of the new U-AGW6-2as the tunnel endpoint address only when the load statuses of the new U-AGW6-2in the case of switching the endpoint satisfies a predetermined condition. If the estimated load status of the new U-AGW6-2does not satisfy the predetermined condition for U-AGW switching, the C-AGW5notifies the BS10B of the address of the current U-AGW6-1as the tunnel endpoint address. In this case, the new tunnel9A(1) for the AT20A is established between the BS10B and the U-AGW6-1so that forwarding of packets to be communicated by the AT20A is controlled by the same U-AGW6-1as before.

FIG. 5shows the format of a Registration Request (RRQ) message80of Proxy Mobile IP (PMIP) as an example of a tunnel setup request message to be transmitted from each base station (BS)10to the C-AGW5.

The RRQ message80comprises a message body81and an extension part82. The message body81is a main part other than the extension part of a Registration Request message described in IETF RFC3344, section 3.3, and includes a message type81aindicating that this message is RRQ and other information81bincluding IP addresses, etc. The extension part82includes a mobile station identifier (ATID)83, a binding type84indicative of the type of tunnel, and other information85. The binding type84includes information for discriminating whether the tunnel requested to be set up by the RRQ message80is the first tunnel (“Primary”) for the mobile station specified by ATID83or the second or subsequent tunnel (“Reverse Link (RL) Only”) to be set up for upward data transmission. The other information85includes information such as a service class required by the AT.

FIG. 6shows the format of a PMIP RRP message90to be returned from the C-AGW5to the BS10as a reply message in response to the RRQ message80.

The RRP message comprises a message body91and an extension part92. The message body91is a main part other than the extension part of a Registration Reply message described in IETF RFC3344, section 3.4, and includes a message type91aindicating that this message is RRP and other information91bindicating IP addresses, etc. The extension part92includes the mobile station identifier (ATID)93, a tunnel endpoint94, and other information95. In the field of tunnel endpoint94, the IP address of U-AGW having been selected from among the U-AGWs6-1to6-mby the C-AGW5is set.

FIG. 7shows the format of a User QoS Profile message70to be transmitted from the AAA-server3to the C-AGW5.

The User QoS Profile message comprises a control information part71, a mobile station identifier (ATID)72, and a user QoS profile73representing a communication service quality (QoS) ensured to the AT identified by the ATID72. The control information part71includes a message type indicating that this message70is a user QoS profile message and other information. The user QoS profile73includes, for example, priority74of communication service, a maximum bandwidth (BW)75available for the AT, and other information76.

FIG. 8is a block structural diagram sowing an embodiment of the C-AGW5. The C-AGW5comprises a controller (processor)51, a program memory52for storing protocol processing routines and other control programs to be executed by the controller51, a data memory53, a network interface (NW-INF)54-1for connecting to the core network1, a network interface (NW-INF)54-2for connecting to the access network8, an AGW interface (AGW-INF)55for connecting to the AGW internal bus40, a user interface56, and an internal bus50interconnecting the above mentioned components. In the data memory53, a U-AGW status table57, a QoS information table58, a U-AGW address table59, and other data storage areas are formed.

FIG. 9is a block structural diagram sowing an embodiment of the U-AGW6. The U-AGW6comprises a controller (processor)61, a program memory62for storing various control programs to be executed by the controller61, a data memory63, a network interface (NW-INF)64-1for connecting to the core network1, a network interface (NW-INF)64-2for connecting to the access network8, an AGW interface (AGW-INF)65for connecting to the AGW internal bus40, and an internal bus60interconnecting the above mentioned components.

In the program memory62, a control program for measuring the load status of the U-AGW6and periodically notifying the C-AGW5of the measured load status is stored. In the data memory63, a buffer area64comprising a transmission buffer area for temporarily storing transmission packets and a reception buffer area for temporarily storing received packets is formed. The network interface (NW-INF)64-2for connecting to the access network8may be connected to the access network8, together with the NW-INFs64-2of the other U-AGWs in the same AGW4, via a packet switch associated with the AGW4.

FIG. 10illustrates an embodiment of the U-AGW status table57formed in the memory53of the C-AGW5.

The U-AGW status table57comprises a plurality of table entries corresponding to the U-AGWs6-1to6-mconnected to the C-AGW5. Each table entry includes, as U-AGW load status information in association with U-AGW address571, for example, a use rate of CPU572, a use rate of buffer573, and other information574. The use rate of buffer573varies depending on the number of user packets waiting for being processed in the reception buffer area of the U-AGW. The other information574includes, for example, a communication bandwidth of U-AGW and a use rate of the bandwidth.

FIG. 11illustrates an embodiment of the QoS information table58formed in the memory53of the C-AGW5.

The QoS information table58comprises a plurality of table entries, each of which indicates the relation between the mobile station identifier (ATID)581and user QoS profile582. The user QoS profile582indicates, for example, a priority582A of communication service or resource allocation for a mobile station identified by the ATID581, a maximum bandwidth (BW)582B available for the mobile station, a communication service class (Allowed Service Class)582C, and a maximum CPU occupation rate582D allowed for the mobile station. As the communication service class, information for specifying a communication service class ensured to the AT user by a contract beforehand, for example, a service class of data communication, voice communication, or video communication is stored.

FIG. 12illustrates an embodiment of the U-AGW address table59formed in the memory53of the C-AGW5.

The U-AGW address table59comprises a plurality of table entries, each of which indicates, in association with a mobile station identifier (ATID)591, a U-AGW address592, a base station (BS) address593, and a binding type594. The U-AGW address592and the BS address593represent IP addresses of the U-AGW and the base station to be the endpoints of a tunnel for forwarding user packets, respectively. As the binding type594, “Primary” is stored when the tunnel established between a base station designated by the BS address593and a U-AGW designated by the U-AGW address592is the only one for the mobile station having the ATID591and “RL Only” is stored when the tunnel is the second or subsequent one coexisting with the first tunnel.

In the case where a management apparatus for supervising the session status of each mobile station is located as an entity governing the BS, for example, each base station may decide whether the binding type should be “Primary” or “RL Only” in accordance with control information supplied from the management apparatus.

InFIG. 12, for example, a table entry EN1indicates that the tunnel (tunnel9A inFIG. 2) established between the base station10A having the IP address “IP10A” and the U-AGW6-1having the IP address “IP6-1” is the first tunnel for the AT20A. Likewise, a table entry EN2indicates that the tunnel (tunnel9B inFIG. 2) established between the base station10B having the IP address “IP10B” and the U-AGW6-2having the IP address “IP6-2” is the first tunnel for the AT20B.

FIG. 13illustrates the first embodiment of a signaling sequence for establishing a tunnel for forwarding user data between the base station10and one of U-AGWs6-1to6-min the mobile communication system of the present invention.

Here, a signaling sequence will be explained, similarly toFIG. 4, about the case where the AT20A is connected to the core network1, in the wireless access network shown inFIG. 2, but the explanation for the same part as the conventional signaling sequence described with respect toFIG. 4will be simplified by applying the same reference symbols as used inFIG. 4.

In the present embodiment, each U-AGW6(6-1to6-m) periodically measures the use rate of CPU, the use rate of buffer, and other resource parameter values indicative of its load status and notifies the C-AGW5of the status information indicating the above mentioned values by a U-AGW status notification message (SQ01). Although transmission of the U-AGW status notification message from each U-AGW6to the C-AGW5is repeated periodically, this transmission is typified by SQ01inFIG. 13for simplification. Upon receiving a U-AGW status notification message from one of U-AGWs6, the C-AGW5updates the load status information such as the use rate of CPU572, use rate of buffer573, and other information574in a table entry corresponding to the source address (the U-AGW address) of the received message in the U-AGW status table57.

In the access authentication procedure SQ10ato SQ10cfor authenticating the mobile station (AT)20A shown inFIG. 13, when succeeded in the access authentication (including user authentication) of the AT20A, the AAA server3transmits to the C-AGW5the user QoS profile including the priority, maximum BW, service class, maximum CPU occupation rate, etc. allowed for the AT20A as a User QoS profile message (SQ13).

Upon receiving the User QoS profile message from the AAA server3, the controller51of the C-AGW5executes a user QoS profile receiving routine, not shown inFIG. 8, and checks whether the AT identifier (ATID) notified from the AT20A at step SQ12inFIG. 13has already been registered as ATID581in the QoS information table58. If the ATID of the AT20A is not registered yet in the QoS information table58, the controller51adds a new table entry indicating the correspondence of the ATID to the user QoS profile notified from the AAA server3into the QoS information table58. When the ATID of the AT20A has already been registered as ATID581in the QoS information table58, the controller51terminates the user QoS profile receiving routine without updating the QoS information table58.

Upon completion of the access authentication of the AT user, the BS10A performs configurations (SQ14a, SQ14b) for connecting with the AT20A through a wireless channel. After that, the BS10A transmits to the C-AGW5a tunnel setup request (PMIP RRQ) message80to establish a tunnel for forwarding user data (SQ15). The request message includes the identifier (ATID)83of the AT20A and the binding type84as shown inFIG. 5.

Upon receiving the tunnel setup request (PMIP RRQ) message80, the controller51of the C-AGW5refers to the U-AGW status table57to select a U-AGW being in the lowest load status among the U-AGWs6-1to6-mas the U-AGW to be assigned to the AT20A. In this example, U-AGW6-11sselected as the U-AGW to be assigned to the AT20A. Then, the controller51returns to the BS10A a response (PMIP RRP) message90shown inFIG. 6which includes the IP address of the U-AGW6-1as the tunnel endpoint94(SQ16). At this time, the controller51updates the U-AGW address table59in the memory53by adding a new table entry that indicates, in association with the ATID93specified in the PMIP RRQ message, the IP address of the U-AGW6-1to be the tunnel endpoint, the IP address of the base station having transmitted the PMIP RRQ message, and the binding type84indicated in the PMIP RRQ message80.

FIG. 14illustrates an RRQ receive processing routine200to be executed by the controller51in response to receiving the tunnel setup request (PMIP RRQ) message.

In the RRQ receive processing routine200, the controller51selects a U-AGW (address) being now in the lowest load status, based on the use rate of CPU572, use rate of buffer573, and other information574indicated in the U-AGW status table57(step201). It is assumed here that U-AGW6-1was selected as the U-AGW being in the lowest load status.

The controller51then checks whether the requesting ATID83specified in the received PMIP RRQ message80has already been registered as the ATID591in the U-AGW address table59(step202). It is assumed here that the requesting ATID83is not yet registered in the U-AGW address table59and the PMIP RRQ message80has been transmitted from the base station10A to the C-AGW5. In this case, the controller51assigns a new U-AGW (U-AGW6-1in this example) selected at step201to the AT20A (211) and adds to the U-AGW address table59a new table entry EN-1indicating the correspondence among the ATID83of the requesting AT and the binding type84specified in the PMIP RRQ message80, the IP address of the U-AGW6-1, and the IP address of the base station having transmitted the PMIP RRQ message80(212). After that, the controller51returns a reply (PMIP RRP) message90including the IP address (“IP6-1) of the U-AGW6-1as the tunnel endpoint94to the base station10A having transmitted the PMIP RRQ message90(213, SQ16inFIG. 13) and terminates the RRQ receive processing routine200.

In the case where the requesting ATID specified in the PMIP RRQ message90has already been registered as ATID591in the U-AGW address table59, as in the case of AT handover between base stations which will be described later, that is, when the PMIP RRQ message80was transmitted from the base station10B to which the AT20A is going to be handed over, the controller51compares the address of new U-AGW selected at step201and the address of current U-AGW registered in association with the requesting ATID in the U-AGW address table59(203). If the address of the new U-AGW matches with the address of the current U-AGW, the controller51assigns the address of the current U-AGW indicated in the U-AGW address table to the AT20A (206A).

If the address of the new U-AGW does not match with the address of the current U-AGW, for example, in the case where the current U-AGW is U-AGW6-1and the new U-AGW is U-AGW6-2, the controller51estimates the load status of the new U-AGW6-2in the case of switching the endpoint of tunnel from the current U-AGW6-1to the new U-AGW6-2, based on the current load status information of the new U-AGW6-2indicated in the U-AGW status table57and the user QoS profile information of the requesting AT20A indicated in the QoS information table58(204). After that, the controller51determines whether the predetermined condition for U-AGW switching is satisfied or not by comparing the estimated load status of the new U-AGW6-2and the load status of the current U-AGW6-1(205).

For example, in the case where L1stands for the load of the current U-AGW6-1indicated in the U-AGW status table57, L2the load of the new U-AGW6-2and ΔL a load occupied by the requesting AT, L1and L2are in a relation L1>L2now because the new U-AGW6-2is in the lowest load status. When the endpoint of the tunnel for the requesting AT is switched from the current U-AGW6-1to the new U-AGW6-2, the load of the current U-AGW6-1changes from L1to L1−ΔL and the load of the new U-AGW6-2changes from L2to L2+ΔL.

Here, if L1is larger than L2+ΔL, the difference between the load of U-AGW6-1and the load of U-AGW6-2can be made smaller than the current state by switching the tunnel endpoint from the current U-AGW6-1to the new U-AGW6-2and a load distribution effect is obtained. However, if L1is smaller than L2+ΔL, the switching of the tunnel endpoint from the current U-AGW6-1to the new U-AGW6-2makes the difference between the load L1−ΔL of the current U-AGW6-1and the load L2+ΔL of the new U-AGW6-2larger than the current state. In this case, the tunnel endpoint switching has an adverse effect on load distribution.

The U-AGW switching condition at step205means a conditional expression for determining whether the tunnel endpoint switching contributes to load distribution, based on the load state of the current U-AGW6-1and the estimated load state of the new U-AGW6-2in the case of switching the tunnel endpoint. When the new U-AGW6-2is in the lowest load status, the relation L1≧L2is satisfied inevitably. In this case, the tunnel endpoint switching contributes to load distribution if the loads L1, L2and ΔL are in a relation L1−L2>ΔL.

The controller51assigns the address of the current U-AGW indicated in the U-AGW address table59to AT20A when the U-AGW switching condition is not satisfied (206A), and assigns the address of the new U-AGW selected at step201to the AT20A only in the case where the U-AGW switching condition is satisfied (206B). After assigning the U-AGW address to the AT20A, the controller51determines the binding type84specified in the PMIP RRQ message80(207).

When the biding type indicates “RL Only”, that is, in the case where the mobile communication system shown inFIG. 1has a system configuration that allows establishing a plurality of tunnels for the same AT, the controller51adds a new table entry EN-1to the U-AGW address table59(212). The new table entry EN-1indicates the correspondence among the ATID83of requesting AT and the binding type84specified in the PMIP RRQ message80, the IP address of the current U-AGW6-1, and the source IP address of the PMIP RRQ message80indicating the BS10A (212). After that, the controller51returns a reply (PMIP RRP) message specifying the IP address of the U-AGW assigned at step206A or206B as the tunnel endpoint94, to the base station10B having transmitted the PMIP RRQ message and terminates the routine200.

When the binding type in the PMIP RRQ message80indicates “Primary”, the controller51rewrites the BS address593of the table entry registered in the U-AGW address table59to the address of the base station10B having transmitted the PMIP RRQ message (208). After that, the controller51returns a reply (PMIP RRP) message specifying the IP address of the U-AGW assigned at step206A or206B as the tunnel endpoint94, to the base station10B having transmitted the PMIP RRQ message (209), releases the existing tunnel having been used before the handover (210), and terminates the routine200.

Returning toFIG. 13, when the PMIP RRP message90is received from the C-AGW5, the BS10A establishes a tunnel toward the U-AGW6-1according to the IP address “IP6-1” of U-AGW specified by the “Endpoint”94in the received message (SQ18), whereby the AT20A becomes in the state capable of communicating user data with the correspondent node via the BS10A and the U-AGW6-1(SQ19a, SQ19b, SQ19c).

Next, a description will be made by referring toFIG. 15about a signaling sequence of an AT handover to be performed when the AT20A has moved from the coverage area of BS10A into the coverage area of BS10B shown inFIG. 2. InFIG. 15, as the sequences SQ10ato SQ19care the same as those inFIG. 13, their description will be omitted.

Assume here that the AT20A being in the state of communication through the tunnel established between the base station10A and the U-AGW6-1has moved into the coverage area (service area) of the BS10B. The AT20A monitors the status of radio channel for each base station periodically, for example, by measuring the quality of pilot signals received from the base stations10A and10B or by communicating control information with each base station.

When the status of the radio channel of the new base station10B has become better than that of base station10A, the AT20A starts a procedure to handover the AT20A from the base station10A to the base station10B. The handover of AT20A, however, may be initiated by the base station10A or10B.

Upon receiving a handover request from the AT20A, the base station10B performs the access authentication procedure of AT20A, with the AAA server3via the SRNC7and the C-AGW5(SQ20a, SQ20b, SQ20c). In this case, similarly to the first access authentication procedure (SQ10a, SQIOb, SQ10c) detailed inFIG. 13, the IP address of C-AGW5to which the base station10B is linked is notified from the C-AGW5to the base station10B, the identifier (ATID) of the AT20A is notified from the AT20A to the C-AGW5, and the user QoS profile corresponding to the ATID is notified from the AAA server3to the C-AGW5.

Upon receiving the user QoS profile from the AAA server3, the controller51of the C-AGW5executes the user QoS profile receive processing routine. This time, as the table entry corresponding to the ATID of the AT20A has already been registered in the QoS information table58, update of QoS information table58is not carried out.

Upon completing the access authentication procedure (SQ20a, SQ20b, SQ20c), the base station10B performs configurations (SQ24a, SQ24b) for communicate with the AT20A through a wireless channel, and transmits a tunnel setup request (PMIP RRQ) message80to the C-AGW5(SQ25). The PMIP RRQ message80transmitted from the base station10B to the C-AGW5includes the identifier (ATID) of the AT20A and “Primary” as its binding type.

Upon receiving the PMIP RRQ message80from the base station10B, the controller51of the C-AGW5selects a U-AGW to be assigned to the AT20A by executing the RRQ receive processing routine200described by referring toFIG. 14. This time, as the table entry EN1corresponding to the identifier (ATID) of the AT20A has already been registered in the U-AGW address table59, the controller51assigns U-AGW6-j(current U-AGW or new U-AGW) to the requesting AT20A according to steps203to206A or206B and updates the U-AGW address table59. After that, the controller51returns to the base station10B a reply (PMIP RRP) message90specifying the IP address of the U-AGW6-jby the “Endpoint”94(step209, SQ26inFIG. 15).

After transmitting the PMIP RRP message90, the controller51releases the existing tunnel9A between the base station10A and the U-AGW6-1, for example, by transmitting a tunnel release message to the base station10A (step210, SQ27inFIG. 15). The tunnel may be released by instructing the U-AGW6-1to release the tunnel from the controller51through the AGW internal bus and by transmitting a tunnel release message from the U-AGW6-1to the base station10A. The existing tunnel is released, for example, by timer control when a predetermined time passed after the PMIP RRP message was transmitted.

Upon receiving the reply (PMIP RRP) message90from the C-AGW5, the base station10B establishes a tunnel toward the U-AGW6-j(e.g., U-AGW6-1in this example) specified by the “Endpoint” (SQ28), whereby the AT20A becomes in the state capable of communicating user data via the base station10B and U-AGW6-j(SQ29a, SQ29b, SQ29c).

According to the present embodiment, when a handover of AT20A occurs, the C-AGW5selects a new U-AGW being now in the lowest load status, but assigns the same U-AGW6-1as used before the handover to the tunnel endpoint after the handover of the AT20A unless the load of the new U-AGW estimated in the case of switching the tunnel endpoint satisfies the predetermined condition of U-AGW switching. It is possible, therefore, to realize inter-base station handover of AT without requiring route change between the AGW4and the core network. Further, by switching the tunnel endpoint to the new U-AGW when the estimated load of the new U-AGW satisfies the condition of U-AGW switching, the difference between the load of the new-AGW and the load of the current U-AGW can be decreased than the current state. It is possible, therefore, to optimize the load distribution over the U-AGWs each time the tunnel endpoint switching occurs.

In the embodiment ofFIG. 15, when the AT20A has moved from the coverage area of the base station (BS)10A into the coverage area of the base station (BS)10B, a new tunnel (tunnel9A(1) or9A(2) inFIG. 2) is established between the base station10B and the U-AGW6-jand the existing tunnel (tunnel9A inFIG. 2) having been established between the base station10A and the U-AGW6-1is released. On the other hand, according to the RRQ receive processing routine200illustrated inFIG. 14, when the binding type84indicates “RL Only” in the tunnel setup request (PMIP RRQ) message80, a new tunnel can be established between the base station10B and the U-AGW6-j, while the existing tunnel between the base station10A and the U-AGW6-1remains.

In the above described embodiment, a tunnel (reverse link: “RL Only”) for upward transmission is established as a new tunnel9A(1) or9A(2) for the AT20A in the state where the first tunnel (reverse link/forward link: “Primary”)9A for bidirectional transmission has been established. Such a tunnel setup function is provided in the above-mentioned UMB (Ultra Mobile Broadband) wireless system.

If the AT handover is controlled so as to promptly hand over the AT20A from the base station10A to the base station10B when the AT20A has entered the coverage area of the BS10B, a reverse handover from the base station10B to the base station10A would occur when the AT20A has returned to the coverage area of the BS10A. Since establishing a tunnel between base station and U-AGW6needs a certain period of time, the load of the C-AGW5increases with frequent handovers between base stations. However, by establishing tunnels (9A and9A(1) or9A(2)) in parallel toward the AGW4from two base stations (BS10A and BS10B inFIG. 15) having a high possibility of AT handover between them, it becomes possible to prevent the load of the C-AGW5from increasing due to inter-base station handovers, even when the AT20A wanders across the boundary between the coverage areas of the base stations10A and108.

In the present embodiment, when a new tunnel9A(1) or9A(2) for the AT20A is established via the base station108in a state where the tunnel9A for the AT20A via the base station10A exists already, the controller51of the C-AGW5selects a new U-AGW being now in the lowest load status and estimates the load of the new U-AGW in the case of changing the tunnel endpoint in order to designate, as the endpoint of the new tunnel, the address of U-AGW acting as the endpoint of the exiting tunnel, unless the estimated load satisfies a predetermined condition. The present embodiment, therefore, has an advantage that the forwarding of data packets for the AT20A can be continuously controlled by the same U-AGW within the AGW4even if the AT20A moves.

In the determination step of the U-AGW switching condition, for example, use rate of buffer573may be used as values of L1and L2instead of use rate of CPU572indicated in the U-AGW status table57inFIG. 10. In this case, a value ΔL of use rate of buffer to be occupied by the AT20A may be estimated from the user QoS profile of AT20A in the QoS information table58, for example, from the value of maximum BW or the service class. As values of L1and L2, use rate of bandwidth is also usable. In this case, the load status of two U-AGWs after tunnel endpoint switching can be estimated by applying the value of maximum BW indicated by the user QoS profile to ΔL and the values of use rate of bandwidth included as the other information in the U-AGW status table57to L1and L2.

The controller51may calculate estimation values of consumed communication resources for each of the U-AGWs provided in the AGW4, store the estimation values into the U-AGW status table57, and select one of the U-AGWs whose consumed resources are the smallest as a new U-AGW. The consumed resources for each U-AGW can be obtained from the U-AGW address table59and the QoS information table58. For example, in the case where a total amount of maximum bandwidths ensured to ATs is adopted as the amount of consumed resources, the controller51may read out plural pairs of ATID591and U-AGW address592from the U-AGW address table59one after another, retrieve the value of maximum BW582B corresponding to the ATID591from the QoS information table58, and accumulate the retrieved maximum BW value in the U-AGW status table57as the amount of consumed resources corresponding to the U-AGW address592. In this case, the controller51may estimate the load L+ΔL of a new U-AGW in the case of switching the tunnel endpoint, by applying the maximum BW value of the AT to be handed over to ΔL and determine whether the U-AGW switching condition is satisfied or not based on the value of ΔL and the amount of consumed resources L of the current U-AGW.

The controller51may count the number of ATs having the highest priority582A for each U-AGW (IP address) and select a new U-AGW by applying the number of ATs having the highest priority to the amount of consumed resources. Further, the controller51may select a new U-AGW being in the lowest load status, by taking account of both of the load status information shown inFIG. 10notified from each U-AGW and the amount of communication resources for each U-AGW obtained from the above-mentioned U-AGW address table59and QoS information table58.

When a tunnel setup request for a VoIP tunnel is received by the AGW4in the case where some of the plurality of U-AGWs composing the AGW4are especially optimized, for example, to forward VoIP data packets, the controller51may identify the service class582C indicated in user QoS profile and select a new U-AGW having the smallest estimated amount of consumed resources from a group of VoIP optimized U-AGWs. Here, the VoIP optimization is realized by optimizing hardware or software of the U-AGW. Optimizing hardware includes, for example, increasing the capacity of data memory63, speeding up the controller (processor)61, speeding up the network INF64, and so on. Optimizing software includes, for example, specializing the software to be stored in the program memory62, addition of new functions according to service types, and so on.

FIG. 16shows, as another embodiment of the present invention, an example of application of the invention to a mobile communication system complying with 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution), which is a new communication standard for mobile phones under study in the 3GPP standardization organization.

In the LTE wireless communication system, each mobile station21(21A,21B, . . . ) is called a User Equipment (UE), each base station11(11A,11B,11C, . . . ) is called E-UTRAN Node B (eNB), and a session control apparatus70is called a Mobility Management Entity (MME).

InFIG. 16, each eNB11is connected to a Serving Gateway (S-GW)4A and the MME70belonging to an access network. The S-GW4A is an access gateway (AGW) provided with a function of packet forwarding and routing control. The S-GW4A is connected to the MME70belonging to the access network, and connected to a Public Data Network Gateway (P-GW)4B, a Home Subscriber Server (HSS)31, and a Policy and Charging Rules Function (PCRF)32, each of which belongs to the core network1. The HSS31is a node for storing subscriber information and the PCRF32is a node for performing a user authentication and accounting processing.

The S-GW4A comprises a C-AGW5A for handling control messages and a plurality of U-AGWs6A-1to6A-n for forwarding user data. Like the C-AGW5in the first embodiment, the C-AGW5A is provided with the U-AGW status table57, QoS information table58, and U-AGW address table59. When UE handover occurs, the C-AGW5A changes the U-AGW to be a tunnel endpoint from a current U-AGW to a new U-AGW being in the lowest load status only when a predetermined U-AGW switching condition is satisfied.

The P-GW4B is a gateway provided with an accounting function of charging depending on a service level and a function of assigning an IP address to each UE21. The P-GW4B comprises a C-AGW5B for handling control messages and a plurality of U-AGWs6B-1to6B-n for forwarding user data. Like the C-AGW5in the first embodiment, the C-AGW5B is also provided with the U-AGW status table57, QoS information table58, and U-AGW address table59. When UE handover occurs, the C-AGW5B changes the U-AGW to be a tunnel endpoint to a new U-AGW being in the lowest load status only when the U-AGW switching condition is satisfied.

FIG. 17illustrates an example of a signaling sequence for establishing tunnels for forwarding user data among the UE21A, the eNB11A, the S-GW4A and the P-GW4B when connecting the UE21A to the core network1.

In advance of transmitting a service request message, the UE21A establishes an RRC connection with an eNB11A (SQ31). When the UE21A transmits a service request message to the eNB11A (SQ32a), the eNB11A forwards the received service request message to the MME70(SQ32b). Upon receiving the service request message, the MME70assigns a call identifier (MME_UE_SIAP_ID) different for each UE to the user ID (UE-ID) specified in the received service request message and notifies the UE21A of the call identifier (SQ33). Meanwhile, in the S-GW4A, each of the U-AGWs6A-1to6A-m periodically notifies the C-AGW5A of its load status information (SQ01). Similarly, in the P-GW4B, each of the U-AGWs6B-1to6B-m periodically notifies the C-AGW5B of its load status information (SQ02).

Upon receiving the call identifier (MME_UE_SIAP_ID) from the MME70, the UE21A starts an access authentication procedure with the HSS31via the C-AGW5A of the S-GW4A (SQ34). In the access authentication procedure, the C-AGW5A of the S-GW4A selects a U-AGW to be connected to the UE21A, for example, a U-AGW6A-1being in the lowest load status by referring to the load status information of the U-AGWs6A-1to6A-m and notifies the MME70of the IP address of the selected U-AGW6A-1as a connection point of the UE21A (SQ35).

On the other hand, in the P-GW4B, the C-AGW5B selects a U-AGW to be assigned to the UE21A, for example, a U-AGW6B-1being in the lowest load status by referring to the load status information of the U-AGWs6B-1to6B-m. The IP address of the selected U-AGW6B-1is notified as a connection point of the UE21A from the C-AGW5B to the C-AGW5A of the S-GW4A (SQ36).

Upon receiving the connection point of UE21A from the S-GW4A, the MME70notifies the eNB11A of the connection point by transmitting an Initial Context Setup Request message of S1-AP (S1Application Protocol) which is an application layer protocol between eNB and MME (SQ37). The eNB11A requests the UE21A to establish a Data Radio Bearer (DRB) and a Signaling Radio Bearer (SRB) by transmitting an RRC Connection Configuration message (SQ38).

Upon receiving the RRC Connection Configuration message, the UE21A establishes a reverse link (uplink) tunnel toward the eNB11A (SQ39a). Then, the eNB11A establishes a reverse link tunnel toward the U-AGW6A-1(SQ39b) and the U-AGW6A-1establishes a reverse link tunnel toward the U-AGW6B-1(SQ39a), whereby the UE21A becomes transmittable uplink data.

The UE21A having established the reverse link tunnel transmits an RRC Connection Configuration Complete message to the eNB11A (SQ40). Upon receiving the RRC Connection Configuration Complete message, the eNB11A transmits an Initial Context Setup Complete message indicating the IP address of the eNB11A to the MME70(SQ41). The MME70notifies the C-AGW5A in the S-GW4A of the IP address of the eNB11A by transmitting an Update Bearer Request message (SQ42). Upon receiving the Update Bearer Request message from the MME70, the C-AGW5A returns a reply message (Update Bearer Response) to the MME70(SQ44).

After establishing the reverse link (uplink) tunnel between the U-AGW6A-1and the U-AGW6B-1at SQ39a, the U-AGW6B-1establishes a forward link (downlink) tunnel toward the U-AGW6A-1(SQ43a), the U-AGW6A-1establishes a forward link tunnel toward the eNB11A (SQ43b), and the eNB11A establishes a forward link tunnel toward the UE21A (SQ43c), whereby downlink data transmission from the U-AGW6B-1to the UE21A becomes possible. Then, as indicated by SQ45ato SQ45c, the UE21A transits into the state capable of communicating user data with a correspondent UE connected to the core network1, via the tunnels established among the e-NB11A, the U-AGW6A-1and the U-AGW6B-1.

When the UE21A has moved into the coverage area of another eNB11B from the coverage area of the eNB11A, the sequence similar toFIG. 17is performed by the eNB11B, MME70, S-GW4A, and P-GW4B in turn. In this case, each of the C-AGWs6A-1and6B-1decides the U-AGW to be the tunnel endpoint, similarly to the first embodiment, by determining whether the U-AGW switching condition is satisfied.

As apparent from the above-described embodiments, the C-AGW according to the present invention selects, in response to a tunnel setup request, a new U-AGW being in the lowest load status from among a plurality of U-AGWs belonging to the same AGW, but when AT (or UE) handover occurs in association with the tunnel setup request, the C-AGW estimates the load status of the new U-AGW in the case of switching the tunnel endpoint so as to designate the new U-AGW as the tunnel endpoint only when the estimated load status of the new U-AGW satisfies a predetermined switching condition.

According to the present invention, because the current U-AGW is assigned as the tunnel endpoint after the AT handover unless the estimated load status of the new U-AGW satisfies the switching condition, packets forwarding for the AT after the handover can be performed by the same U-AGW continuously. In the case where the tunnel endpoint has been changed, optimum load distribution among the U-AGWs can be achieved.

The present invention can also be applied to other wireless communication systems such as WiMax, in addition to the 3GPP2 UMB wireless communication system and the 3GPP LTE wireless communication system presented in the embodiments.