System and associated method of maintaining packet switching capability in a cellular network

A mobile station performs location registration to one of exchanges managing a location registration area where the mobile station is located, in a mobile communication system in which a plurality of exchanges manage one location registration area and a radio network controller is connected to the plurality of exchanges. The mobile station includes a communication controller configured to stop transmission of signals to the radio network controller, when an identifier of an exchange notified by an access restriction signal from the radio network controller matches an identifier of an exchange which has performed the location registration of the mobile station.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. P2004-108113, filed on Mar. 31, 2004; the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication method in which a mobile station performs location registration to one of exchanges managing a location registration area where the mobile station is located, in a mobile communication system where a plurality of exchanges manage one location registration area and a radio network controller is connected to the plurality of exchanges.

The present invention also relates to a mobile station and a radio network controller which can be used in the mobile communication method.

2. Description of the Related Art

Conventionally, a mobile communication system in which one location registration area is managed by a plurality of exchanges so that processing load in each exchange can be dispersed is known. Referring toFIGS. 1A and 1B, this type of mobile communication system will be explained.

In this mobile communication system, as shown inFIG. 1A, a radio network controller RNC is connected to a first exchange for a packet switched service SGSN (Serving GPRS Support Node) #1and a second exchange for a packet switched service SGSN #2, which manage a same routing area (location registration area) RA #1, via predetermined interfaces (e.g. Iu-flex interfaces).

When receiving a location registration request from a mobile station UE in the routing area RA #1, the radio network controller RNC is configured to determine an SGSN to which the mobile station UE performs the location registration, in accordance with the load status in each SGSN.

The radio network controller RNC is configured to transfer the location registration request from the mobile station UE to the determined SGSN.

InFIG. 1A, a mobile station UE #1performs the location registration to the first SGSN #1in the routing area RA #1, and transmits signals for each type of packet switched service via the first SGSN #1.

On the other hand, a mobile station UE #2, which is located in the same routing area RA #1, performs the location registration to the second SGSN #2, and transmits signals for each type of packet switched service via the second SGSN #2.

However, in the conventional mobile communication system, there has been a problem in that, in the case where congestion or failure occurs in one of a plurality of SGSNs managing a same routing area RA #1, not only mobile stations UE registered in the SGSN but also mobile stations UE registered in other SGSNs fail to transmit signals for each type of packet switched service to the registered SGSN, that is, those mobile stations UE cannot use packet switched service in that situation.

Specifically, as shown inFIG. 1B, when congestion or failure occurs in the first SGSN #1, in step S1, the first SGSN #1transmits a state signal to the radio network controller RNC, so as to notify the occurrence of the congestion or the failure, in step S2.

In step S3, the radio network controller RNC broadcasts an access restriction signal, which restricts accesses to the packet switched service domain, to mobile stations UE in the routing area RA #1.

Here, in the conventional mobile communication system, the radio network controller RNC cannot identify the first SGSN #1where the congestion or the failure occurs, in the access restriction signal.

Therefore, in step S4, the mobile station UE #1stops transmitting signals for each type of packet switched service addressed to the first SGSN #1, in accordance with the received access restriction signal.

And, in step S5, the mobile station UE #2also stops transmitting the signal for each type of packet switched service addressed to the second SGSN #2, in accordance with the received access restriction signal.

Further, in step S6, a mobile station UE #3, which has newly moved into the routing area RA #1from another routing area, cannot transmit a location registration request in routing area PA #1even though the second SGSN #2is available.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in view of the above problems, and has an object of providing a mobile communication method in which a mobile station which has performed the location registration to a second SGSN managing a same location registration area as a first SGSN and a mobile station which has newly moved into the location registration area can access to the second SGSN which is originally available, when congestion or failure occurs in the first SGSN, and a mobile station and a radio network controller which can used in the mobile communication method.

A first aspect of the present invention is summarized as a mobile station for performing location registration to one of exchanges managing a location registration area where the mobile station is located, in a mobile communication system in which a plurality of exchanges manage one location registration area and a radio network controller is connected to the plurality of exchanges. The mobile station includes a communication controller configured to stop transmission of signals to the radio network controller, when an identifier of an exchange notified by an access restriction signal from the radio network controller matches an identifier of an exchange which has performd the location registration of the mobile station.

In the first aspect, the mobile station can further include a mobile station identifier storage configured to store an identifier of the mobile station allocated in a location registration area where the location registration is performed; and the communication controller can be configured to stop transmission of signals to the radio network controller, when an identifier of an exchange notified by the access restriction signal from the radio network controller matches the identifier of an exchange included in the identifier of the mobile station.

In the first aspect, the mobile station can further include a location area identifier storage configured to store an identifier of location registration area where the location registration is performed; and the communication controller can be configured to stop transmission of signals to the radio network controller, when an identifier of an exchange notified by the access restriction signal from the radio network controller matches an identifier of an exchange included in the identifier of the mobile station, and when an identifier of a location registration area notified from the radio network controller matches the identifier of a location registration area stored in the location area identifier storage.

In the first aspect, the mobile station can further include an exchange identifier storage to receive and store an identifier of an exchange which has performed the location registration of the mobile station, from the radio network controller, and the communication controller can be configured to stop transmission of signals to the radio network controller, when an identifier of an exchange notified by the access restriction signal from the radio network controller matches the identifier of an exchange stored in the exchange identifier storage.

In the first aspect, the identifier of the exchange can be configured to uniquely identify each exchanges in a specific location registration area and adjacent location registration areas.

In the first aspect, the communication controller can be configured to restart transmission of signals to the radio network controller, when an identifier of an exchange notified by an access restriction release signal from the radio network controller matches an identifier of an exchange which has performed the location registration of the mobile station.

A second aspect of the present invention is summarized as a radio network controller which is connected to a plurality of exchanges, in a mobile communication system in which the plurality of exchanges manage one location registration area. The radio network controller includes a monitor configured to monitor a state of the plurality of exchanges; an exchange identifier notifier configured to notify an identifier of a specific exchange to a mobile station under control of the radio network controller, when the monitor detects an inaccessibility to the specific exchange; and a location area identifier notifier configured to notify an identifier of the location registration area to a mobile station under control of the radio network controller.

A third aspect of the present invention is summarized as a mobile communication method in which a mobile station performs a location registration to one of exchanges which manage a location registration area where the mobile station is located, in a mobile communication system where a plurality of exchanges manage one location registration area and a radio network controller is connected to the plurality of exchanges. The mobile communication method includes: storing, at the mobile station, an identifier of the mobile station which is allocated in a location registration area where the mobile station has performed the location registration; detecting, at the radio network controller, an inaccessibility to a specific exchange among the plurality of exchanges; notifying, at the radio network controller, an identifier of the specified exchange to a mobile station under control of the radio network controller; notifying, at the radio network controller, an identifier of the location area to a mobile station under control of the radio network controller; and stopping, at the mobile station, transmission of signals to the radio network controller, when an identifier of an exchange notified by an access restriction signal from the radio network controller matches an identifier of an exchange stored in the identifier of the mobile station.

DETAILED DESCRIPTION OF THE INVENTION

<Mobile Communication System According to First Embodiment of the Present Invention>

Referring toFIGS. 2 and 3, a mobile communication system according to the first embodiment of the present invention will be described. The entire configuration of the mobile communication system according to the present invention is mostly the same as the entire configuration of the conventional mobile communication system shown inFIGS. 1A and 1B. A configuration of the mobile communication system according to the present embodiment will be explained, focusing on the difference from the configuration of the conventional mobile communication system.

According to the mobile communication system of the present embodiment, a first SGSN #1and a second SGSN #2manage a same routing area (location registration area) RA #1, and a radio network controller RNC is connected to the SGSN #1and the SGSN #2respectively.

A mobile station UE according to the present embodiment is configured to perform the location registration to one of SGSNs which manage a routing area RA where the mobile station UE is located.

As shown inFIG. 2, the mobile station UE includes a transmission and reception unit11, a TMSI storage unit12, an RAI storage unit13, a communication control unit14and a determination unit15.

The transmission and reception unit11is configured to set a radio channel with a base station BS, to transmit signals for a packet of switched service to the radio network controller RNC via the radio channel, and to receive signals such as an access restriction signal from the radio network controller RNC. The signals for a packet switched service includes a location registration request.

The TMSI storage unit12is configured to store a “mobile station identifier” allocated in the routing area where the mobile station UE has performed the location registration.

Specifically, the TMSI storage unit12is configured to store a “temporary user identifier (TMSI: Temporary Mobile Subscriber Identity)” allocated during the location registration.

Here, the TMSI includes an “NRI (Node Resource Indicator)” which is an identifier of an SGSN to which the mobile station UE has performed the location registration. However, the mobile station UE does not know whether or not an NRI is included in TMSI, and cannot detect the NRI from the TMSI by itself.

The RAI storage unit13is configured to store an identifier of the routing area where the mobile station UE has performed location registration.

Specifically, the RAI storage unit13is configured to detect an “RAI (Routing Area Indicator)” from a notification signal periodically transmitted from the radio network controller RNC, and to store the detected RAI.

The communication control unit14is configured to perform necessary controls on communications for a packet switched service.

For example, the communication control unit14is configured to determine to perform the location registration to an SGSN, in such case where the power is turned on or turned off, or the location registration area is changed.

The communication control unit14is configured to transmit a signal for a packet switched service, which is generated in accordance with an instruction from a user, to the radio network controller RNC.

The determination unit15is configured to determine whether or not to transmit a signal for a packet switched service to the radio network controller RNC, in accordance with an access restriction signal or an access restriction release signal broadcasted from the radio network controller RNC.

Specifically, the determination unit15is configured to determine to stop transmitting signals for a packet switched service to the radio network controller RNC, in the case where an NRI of an SGSN notified by an access restriction signal from the radio network controller RNC matches an NRI of an SGSN included in the TMSI, and where an RAI notified by the notification signal from the radio network controller RNC matches an RAI stored in the RAI storage unit13.

The determination unit15is configured to restart transmission of signals for a packet switched service to the radio network controller RNC, in the case where the NRI of the SGSN notified by an access restriction release signal from the radio network controller RNC matches the NRI of the SGSN included in the TMSI, and where the RAI notified by the notification signal from the radio network controller RNC matches the RAI stored in the RA T storage unit13.

The radio network controller RNC according to the present embodiment, a shown inFIG. 3, includes an SGSN #1interface21, an SGSN #2interface22, a UE interface23, an SGSN state monitoring unit24and a signal process unit25,

The SGSN #1interface21is an interface used for communications with the first SGSN #1, and the SGSN #2interface22is an interface used for communications with the second SGSN #2.

The UE interface23is an interface used for communications between mobile stations UE #1and #2in a routing area RA which is managed by the SGSNs connected with the radio network controller RNC. Here, the SGSN41interface21and the SGSN #2interface22constitute an Iu-flex interface.

The SGSN state monitoring unit24is configured to monitor a state of the first SGSN #1and the second SGSN #2.

For example, the SGSN state monitoring unit24is configured to detect an inaccessibility to each SGSNs in accordance with a state signal transmitted from each SGSN. For example, the SGSN state monitoring unit24is configured to detect that the failure occurs in each SGSNs or that the load of each SGSNs crosses a predetermined threshold, in the state signal.

The SGSN state monitoring unit24is configured to also detect the accessibility to each SGSN, in accordance with the state signals transmitted from each SGSN. For example, the SGSN state monitoring unit24is configured to also detect that the failure is recovered in each SGSNs or the load of each SGSNs becomes smaller than the predetermined threshold, in accordance with the state signals.

Further, the SGSN state monitoring unit24may be configured to monitor the load in each SGSN, in accordance with the state signals transmitted from each SGSN.

The signal process unit25is configured to perform a predetermined process on the signals transmitted or received via the interfaces21to23.

Specifically, when receiving a location registration request from a mobile station UE under the control of the radio network controller RNC, the signal process unit25is configured to determine an SGSN for the location registration of the mobile station UE, based on the state of loads in the first SGSN #1and the second SGSN #2. The signal process unit25transfers the location registration request to the determined SGSN.

Here, the location registration request includes a location registration update signal for a packet switched service (Normal Routing Area Update), an attach signal for a packet switched service (GPRS attach) or the like.

The signal process unit25is configured to transfer signals for each type of packet switched service from the mobile station UE under the control of the radio network controller RNC to the SGSN for location registration of the mobile station UE.

The signals for each type of packet switched service may be any signal to be transmitted for using a packet switched service.

The signal process unit25is configured to broadcast, via the UE interface23, an access restriction signal for a relevant SGSN to the mobile station UE under the control of the radio network controller RNC, when detecting an inaccessibility to the SGSN.

The signal process unit25may include the location or bit number or the like of the NRI in the TMSI to the access restriction signal,80as to inform the mobile station UE of an SGSN which is inaccessible.

The signal process unit25may add an NRI to an access restriction signal explicitly, so as to inform the mobile station UE of an SGSN which is inaccessible.

Similarly, the signal process unit25is configured to broadcast an access restriction release signal for relevant SGSN to the mobile station UE under the control of the radio network controller RNC via the UE interface23, when detecting an accessibility to each SGSN.

The signal process unit25is configured to periodically inform the mobile station UE of an identifier of the routing area managed by the SGSN connected with the radio network controller RNC, with using notification signals.

Referring to theFIGS. 4 and 5, an operation of the mobile communication system according to the present embodiment will be explained.

In step S100a, a mobile station UE #1in a routing area RA #1performs the location registration to a first SGSN #1managing the routing area RA #1, obtains an TMSI including an NRI #1of the first SGSN #1from a first radio network controller RNC #1, and stores the obtained TMSI in the TMSI storage unit12.

In step S101a, the mobile station UE #1obtains an RAI #1from the first radio network controller RNC #1and stores the obtained RAI #1in the RAI storage unit13.

Similarly, in step S100b, a mobile station UE #3in a routing area RA #2per forms the location registration to a third SGSN #3managing the routing area RA #2, obtains an TMSI including an NRI #1of the third SGSN #3from a second radio network controller RNC #2, and stores the TMSI in the TMSI storage unit12.

In step S101b, the mobile station UE #1obtains an RAI #2from the second radio network controller RNC #2and stores the RAI #2in the RAI storage unit13.

As described above, the same NRI #1is allocated as the identifier of the first SGSN #1and the identifier of the second SGSN #3.

In step S111, failure or congestion occurs in the first SGSN #1. In step S112, the first SGSN #1transmits a state signal to the first radio network controller RNC #1so as to notify the failure of congestion.

In step S113, the first radio network controller RNC #1detects the occurrence of the failure or the congestion in the first SGSN #1in accordance with the state signal, and broadcasts an access restriction signal including the NRI #1of the first SGSN #1to the mobile station UE #1in the routing area RA #1.

In step S114, the first radio network controller RNC #1transmits a notification signal for notifying the RAI #1, to mobile stations located in the routing area RA #1.

In step S115a, the mobile station UE #1determines that the NRI #1of the first SGSN #1included in the access restriction signal broadcasted from the first radio network controller RNC #1matches the NRI #1of the SGSN included in the TMSI stored in the TMSI storage unit12, and that the RAI #1notified by the notification signal from the first radio network controller RNC #1matches the RAI #1stored in the RAI storage unit13,

The mobile station U S #1stops transmitting signals for a packet switched service to the first radio network controller RNC #1in accordance with the determination results.

On the other hand, in step S115b, the mobile station UE #3which has newly moved into the routing area RA #1determines that the NRI #1of the first SGSN #1included in the access restriction signal broadcasted from the first radio network controller RNC #1matches the NRI41of the SGSN included in the TMSI stored in the TMST storage unit12, and that the RAI #1notified by the notification signal from the first radio network controller RNC #1does not match the RAT #2stored in the RAI storage unit13.

In step S116, the mobile station UE #3transmits a location registration request in the routing area RA #1to the first radio network controller RNC #1in accordance with the determined result.

In steps S117and118, the location registration request from the mobile station UE #3is transferred, via the first radio network controller RNC #1, to the second SGSN #2managing the routing area RA #1, and location registration of the mobile station UE #3is performed in the second SGSN #2.

In the mobile communication system according to the present embodiment, when congestion or failure occurs in the first SGSN #1, the mobile station UE #2which has performed the location registration to the second SGSN #2and the mobile station UE #3which has newly moved into the routing area RA #1can access to the second SGSN #2which is originally available. Here, the location of the mobile station UE42is registered in the second SGSN #2which manages the same routing area RA #1as the first SGSN #1.

<Mobile Communication System According to Second Embodiment of the Present Invention>

Referring toFIG. 5, a configuration of a mobile communication system according to the second embodiment of the present invention will be described, The configuration of the mobile communication system according to the present embodiment will be described, focusing on the difference from the configuration of the mobile communication system according to the first embodiment.

As shown inFIG. 5, the mobile station UE according to the second embodiment includes an SGSN-ID storing unit16, in addition to the elements of the mobile station UE of the first embodiment.

The SGSN-ID storing unit16is configured to store an “SGSN-ID ” of an SGSN to which the mobile station UE has performed location registration.

Specifically, the SGSN-ID storing unit16is configured to receive and store the SGSN-ID transmitted from the radio network controller RNC in a predetermined timing.

The radio network controller RNC may be configured to transmit an SGSN-ID during the process of location registration of the mobile station UE, or to transmit the SGSN-ID after the procedure of location registration of the mobile station UE.

The SGSN-ID is configured to uniquely identify each SGSNs in all routing areas RAs in the mobile communication system. The SGSN-ID typically includes less information than the TMSI in their data amount.

The determination unit15is configured to stop transmitting signals for a packet switched service to the radio network controller RNC, when the SGSN-ID notified by the access restriction signal from the radio network controller RNC matches the SGSN-ID stored in the SGSN-ID storing unit16.

The determination unit15is configured to restart transmitting signals for a packet switched service to the radio network controller RNC, when the SGSN-ID notified by the access restriction release signal from the radio network controller RNC matches the SGSN-ID stored in the SGSN-ID storing unit16.

Referring toFIG. 6, an operation of the mobile communication system according to the present embodiment will be described.

In step S301, a mobile station UE #1in a routing area RA #1performs the location registration to a first SGSN #1which manages the routing area RA #1.

A first radio network controller RNC #1transmits, in a predetermined timing, an SGSN-ID #1of the first SGSN #1to which the location registration of the mobile station UE #1has performed, to the mobile station UE #1. The mobile station UE #1stores the received SGSN-ID #1in the SGSN-ID storing unit16.

Similarly, in step S301b, a mobile station UE #3in a routing area RA #2performs the location registration to a third SGSN #3which manages the routing area RA #2.

A second radio network controller RNC #2transmits, in a predetermined timing, an SGSN-ID #3of the third SGSN #3to which the location registration of the mobile station UE #3has performed, to the mobile station UE #3. The mobile station UE #3stores the received SGSN-ID #3in the SGSN-ID storing unit16.

In step S311, congestion or failure occurs in the first SGSN #1. In step S312, the first SGSN #1transmits a state signal to the first radio network controller RNC #1for notifying the occurrence of the congestion or the failure.

In step S313, the first radio network controller RNC #1detects the congestion or the failure in the first SGSN #1in accordance with the state signal, and broadcasts an access restriction signal including an SGSN-ID #1to mobile stations UB in the routing area RA #1.

In step S314a, the mobile station UE #1determines that the SGSN-ID #1included in the access restriction signal broadcasted from the first radio network controller RNC #1matches the SGSN-ID #1stored in the SGSN-ID storing unit16.

Here, the mobile station UE #1stops transmitting signals for a packet switched. service to the first radio network controller RNC #1in accordance with the determination result.

On the other hand, in step S314b, the mobile station UE #3which has newly moved into the routing area RA #1determines that the SGSN-ID #1included in the access restriction signal broadcasted from the first radio network controller RNC #1does not match the SGSN-ID #3stored in the SGSN-ID storing unit16.

In step S315, the mobile station UE #3transmits a location registration request for the routing area RA #1to the first radio network controller RNC #1in accordance with the determined result.

In steps S316and S317, the location registration request from the mobile station UE #3is transferred, via the first radio network controller RNC #1, to the second SGSN #2which manages the routing area RA #1, and the location registration of the mobile station UE #3is performed in the second SGSN #2.

In the mobile communication system according to the present embodiment, the SGSN-ID can uniquely identify each SGSNs in all routing areas. Therefore, the mobile station UE can control transmission of signals for a packet switched service to the radio network controller RNC by comparing the SGSN-Ids, so that the processing load in the mobile station UE can be reduced.

<Mobile Communication System According to Third Embodiment of the Present Invention>

Referring toFIGS. 7A and 7B, a configuration of the mobile communication system according to the third embodiment of the present invention will be described. The configuration of the mobile communication system according to the third embodiment will be described, focusing on the difference from the configuration of the first embodiment.

As shown inFIG. 7A, a radio network controller RNC according to the present embodiment includes an NRI management unit, in addition to the elements of the radio network controller RNC according to the first embodiment.

The NRI management unit26is configured to manage so that an NRI of an SGSN, in cooperation with other radio network controllers RNC, can uniquely identify each SGSNs in the routing area RA managed by the radio network controller RNC and in the routing areas RAs which are adjacent to the routing area RA.

Specifically, as shown inFIG. 7B, the radio network controller RNC managing the routing area RA #1is configured to manage so that the NRI of the SGSN can uniquely identify each SGSN, in cooperation with the radio network controllers RNC managing the routing areas RAs #2to #7.

However, in the routing areas RAs #1and #8, the same NRI of SGSN can be allocated to different SGSNs.

As described above, a plurality of radio network controllers RNC may work together so as to allocate the NRI of the SGSN, or another independent NRI management device (not shown) may allocate all NRI of the SGSNs.

In the latter case, the NRI management unit26is configured to receive an NRI of an SGSN allocated by the NRI management device.

In the present embodiment, in the routing area RA managed by the radio network controller RNC and in another routing area RA adjacent to the routing area RA, NRIs of each SGSNs are allocated so that each SGSNs can be identified uniquely.

However, the routing area RA to which NRIs of each SGSNs are allocated can be set as other areas, so that the SGSN can be identified uniquely.

Referring to theFIG. 8, an operation of the mobile communication system according to the present embodiment will be described.

In step S401a, a mobile station UE #1in a routing area RA #1performs the location registration to a first SGSN #1which manages the routing area RA #1.

The mobile station UE #1obtains a TMSI including an NRI #1of a first SGSB #1from a first radio network controller RNC #1, and stores the obtained TMSI in the TMSI storage unit12.

Similarly, in step S401b, the mobile station UE #3in the routing area RA #2performs the location registration to a third SGSN #3managing a routing area RA #2.

The mobile station UE #3obtains a TMSI including an NRI #11of the third SGSN #3from a second radio network controller RNC #2, and stores the obtained TMSI in the TMSI storage unit12.

Here, since the routing areas RAs #1and RA #2are adjacent to each other, distinct identifiers are allocated as the NRI #1of the first SGSN #1which manages the routing area RA #1, and as the NRI #11of the third SGSN #3which manages the routing area RA #2.

In step S411, congestion or failure occurs in the first SGSN #1. In step S412, the first SGSN #1transmits a state signal to the first radio network controller RNC #1for notifying the occurrence of the congestion or the failure.

In step S413, the radio network controller RNC #1detects the congestion or the failure in the first SGSN #1in accordance with the state signal, and broadcasts an access restriction signal including the NRI #1of the first SGSN #1to the mobile stations in the routing area RA #1.

In step S414a, the mobile station UE #1detects that the NRI #1of the first SGSN #1included in the access restriction signal broadcasted from the first radio network controller RNC #1matches the NRI #1of the SGSN included in the TMSI stored in the TMSI storing unit12.

Here, the mobile station UE #1stops transmitting signals for a packet switched service to the first radio network controller RNC #1in accordance with the determined result.

On the other hand, in step S414b, the mobile station UE #3which has newly moved into the routing area RA #1determines that the NRI #1of the first SGSN #1included in the access restriction signal broadcasted from the first radio network controller RNC #1does not match the NRI #11of the SGSN included in the TMSI stored in the TMSI storing unit12.

In step S415, the mobile station UE #3transmits a location registration request for the routing area RA #1to the first radio network controller RNC #1in accordance with the determined result.

In steps S416and S417, the location registration request from the mobile station UE #3is transferred, via the first radio network controller RNC #1, to the second SGSN #2managing the routing area RA #1, and the location registration of the mobile station UE #3is performed in the second SGSN #2.

According to the mobile communication system of the present embodiment, NRIs of each SGSNs can identify each SGSNs uniquely, in a predetermined range of routing area. Therefore, the mobile station UE can control the transmission of signals for a packet switched service to the radio network controller RNC by comparing the NRIs of each SGSNs, and the processing load in the mobile station UE can be reduced.

In the present embodiment, examples in that SGSNs are used as exchangers has been explained. However it should be noted that the present invention is not limited to this, and an MSC/VLR (Mobile service Switching Center/Visitor Location Register) can be also applied in the same way. Here, the “MSC/VLR” indicates an exchange for a circuit switched service.

Further, in the present embodiment, routing areas RAs are described as location registration areas. However, it should be noted that the present invention is not limited to this, and a location registration area or the like can be also applied as a location area.

As described above, the present invention can provide a mobile communication method in which a mobile station which has performed the location registration to a second SGSN managing a same location registration area as a first SGSN and a mobile station which has newly moved into the location registration area can access to the second SGSN which is originally available, when congestion or failure occurs in the first SGSN, and a mobile station and the radio network controller which can used in the mobile communication method.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and the representative embodiment shown and described herein. Accordingly, various modifications may be made without departing from the scope of the general inventive concept as defined by the appended claims and their equivalents.