WO2005064978A1

WO2005064978A1 - User registration in a communication system

Info

Publication number: WO2005064978A1
Application number: PCT/IB2004/004053
Authority: WO
Inventors: Kalle Tammi; Anu Leinonen; Minna Myllymaki
Original assignee: Nokia Corporation
Priority date: 2003-12-23
Filing date: 2004-12-07
Publication date: 2005-07-14
Also published as: EP1698202A1

Abstract

A method of reassigning user data in a communications system is disclosed, with a plurality of identities for each user. The method includes storing in a user information store the plurality of identities in association with a first serving controller, the plurality of identities being associated with respective registration statuses selected from a registered status and an unregistered status; detecting that the user has requested registration to a second serving controller using one of the identities; and issuing a registration termination request identifying each identity, which has been newly assigned to the second serving controller as a result of the requested registration. Responsive to the registration termination request, re-registration notification is issued to the user and all identities of the said user from the first serving controller are dissociated.

Description

TITLE:

USER REGISTRATION IN A COMMUNICATION SYSTEM

BACKGROUND OF THE INVENTION:

Field of the Invention:

[0001] The present invention relates to user registration in a communication system.

Description of the Related Art:

[0002] A diverse range of communication systems are in use today enabling

communication between two or more entities, such as user equipment and/or other

nodes associated with the system. Such systems may comprise, for example,

communication of voice, data, and multimedia data.

[0003] Communication systems providing wireless communication for user terminals

or other nodes are known. An example of a wireless system is a public land mobile

network (PLMN). A PLMN is typically a cellular network wherein a base transceiver

station (BTS) or similar access entity serves user equipment (UE) such as mobile

stations (MS) via a wireless interface. The operation of the apparatus required for the

communication is usually controlled by one or more control entities, which themselves

may be interconnected. One or more gateway nodes provide for connecting the PLMN

to other networks. Examples of other such networks are another cellular network, a

public switched telephone network (PSTN) and packet switched data networks such as

an IP (Internet Protocol) based network. The communication between the user

equipment and the other elements of the communication system are based on an appropriate communications protocol, which defines the "rules" under which

communication is handled in the system.

[0004] In the current third generation (3G) wireless system, there are defined various

servers for the handling of different communication services for mobile users. These

include servers that provide call state control functions, known as CSCFs. Control

functions may also be provided by entities such as a home subscriber server (HSS) and

various application servers (AS). The HSS is typically for permanently storing the

user's (subscriber's) profile. For example, in the Release 5 architecture for 3G, as

specified by the 3^rd Generation Partnership Project (3GPP), these entities can be found

located in the IP Multimedia Subsystem (IMS). Call state control function provides a

serving function S-CSCF, an interrogating function, I-CSCF and a proxy function P-

CSCF.

[0005] The IMS network may sit at the hub of the 3G architecture, supporting an IP

based network that handles both traditional voice telephony and multimedia services.

The 3 GPP has chosen Session Initiation Protocol (SIP) as a core session signalling

protocol for 3G networks. SIP has been developed by the Internet Engineering Task

Force (IETF). The 3GPP specification 24.229 describing the IMS network basic

operation from an SIP perspective can be found at

http://www.3gpp.org/ftp/Specs/latest/Rel-5/24_series/24229-560.zip. It should be

noted that SIP is a request/response style protocol, in the sense that for every message

sent from a source, there is an associated response from the destination confirming

receipt of the sent message. [0006] Users are registered with S-CSCFs according to location and available

communication links. The interrogating serving call state control function (I-CSCF) is

used to contact the S-CSCFs. When the S-CSCF which is the assigned S-CSCF for a

user cannot be contacted by the I-CSCF, it is possible to assign a new S-CSCF for a

user during the registration procedure. When this is done, it is possible that the home

subscriber server HSS receives a multimedia authentication request (MAR) command

including an S-CSCF name which is not the same as the previously assigned S-CSCF

for the user. In the existing 3 GPP protocol, the home subscriber server can deregister

the registrations in the old S-CSCF by using the Registration-Termination-Request

(RTR) command. By assigning the reason NEW_SERVER_AS SIGNED to this

command, this causes the user's public identity which is registered in the new S-CSCF

to be deregistered from the old S-CSCF. A subsequent RTR command must then be

issued for the rest of the user's public identities with the deregistration reason set to

SERVER_CHANGE which causes the corresponding user data to be removed from

the old S-CSCF and initiates a deregistration procedure for the user equipment UE to

request the user equipment UE to re-register. The re-registration process is then

directed by the I-CSCF to the new S-CSCF.

[0007] Thus, two individual command sets are required to implement the two

necessary steps, that is the deregistration of the users' public identities from the

previous S-CSCF and the re-registration of the public identities at the new S-CSCF.

SUMMARY OF THE INVENTION: [0008] It is an aim of the present invention to make this procedure more command-

efficient.

[0009] According to one aspect of the present invention there is provided a method of

reassigning user data in a communications system, the user data comprising a plurality

of identities for each user, the method comprising the steps of: storing in a user

information store the plurality of identities in association with a first serving

controller, the plurality of identities being associated with respective registration

statuses selected from a registered status and an unregistered status; detecting that the

user has requested registration to a second serving controller using one of said

identities; issuing a registration termination request identifying the or each identity,

which has been newly assigned to the second serving controller as a result of the

requested registration ; responsive to the registration termination request, i) issuing a

re-registration notification to the user including the or each identity which has a

registered status and which were not assigned to the second serving controller as a

result of the requested registration, and ii) disassociating all identities of the said user

from the first serving controller.

[0010] It will be clear that the re-registration notification causes any unassigned

identities of registered status to be reassigned to the second serving controller.

Unassigned identities of unregistered status need not be reassigned.

[0011] Another aspect provides a communications system comprising: a first serving

controller; a user information store which holds for a user a plurality of identities in

association with the first serving controller, the plurality of identities being associated with respective registration statuses selected from a registered status and an

unregistered status; a second serving controller configured to transfer to the user

information store a user authentication request identifying the user; and wherein the

user information store is operable to detect the user authentication request and

comprises means for inserting into a registration termination request issued to the first

serving controller the or each identity of that user, which were newly associated to the

second serving controller as a result of the user authentication request , and wherein

the first serving controller is operable, responsive to the registration termination

request, to i) issue a re-registration notification to the user including the or each

identity which has a registered status and which were not assigned to the second

serving controller as a result of the user authentication request, and ii) disassociate all

identities of the said user from the first serving controller.

[0012] Another aspect provides a serving controller for use in a system for providing

communication between users, the first serving controller having an interface adapted

to communicate with a user information store whereby a plurality of identities each

with respective registration statuses associate a user with the serving controller and

being operable, responsive to a registration termination request received from the user

information store, to i) issue a re-registration notification to the user including the or

each identity which has a registered status and which incorrectly associate the user

with the first serving controller, and ii) disassociate all identities of the said user from

the serving controller. [0013] In one embodiment, multiple user equipment (equivalent to a private ID) may

share one or more public identities or identity sets. For example, the help desk

employees may share one common public identity SIP:helpdesk@example.com. Each

employee may register/deregister independently, and the serving controller routes the

SIP call request to available employees so that any of them may pick up the call. In

addition, each user equipment may also have non-shared individual public identities.

An aspect of the present invention can be applied in this context to ensure that the

serving controller is the same for all the user equipments sharing the same

identity/identities. Therefore, in one embodiment of the present invention, if any of

the public identities of a sharing user equipment is registered to a new serving

controller, the serving controller is changed for all of those user equipments and their

public identities. To achieve this, the registration termination request (RTR) initiates

deregistration of all of those user equipments and corresponding public identities. To

achieve this, when the serving controller receives a registration termination request, it

can find out, based on locally stored information, if there are any public identities

associated to the user equipment which are shared by another user equipment. If there

is, the serving controller can start the deregistration procedure for all of those user

equipments and their public identities.

[0014] In the 3GPP architecture, the user information store is constituted by the home

subscriber server, but it will be appreciated that in other architectures a different

database may be provided. Also, the first and second serving controllers are provided

by the serving call state control functions in a 3 GPP architecture, but again it will be appreciated that in a different architecture any suitable controller could perform this

role.

[0015] The registration termination request can be an RTR command according to the

known 3G protocol, or can be the equivalent or other suitable command in different

protocols.

BRIEF DESCRIPTION OF THE DRAWINGS:

[0016] For a better understanding of the present invention and to show how the same

may be carried into effect, reference will now be made by way of example to the

accompanying drawings, in which:

[0017] Figure 1 is a schematic diagram showing the environment in which an

embodiment of the invention can be implemented;

[0018] Figure 2 is a schematic diagram illustrating the storage of user identities; and

[0019] Figure 3 is a schematic diagram illustrating the message flow.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:

[0020] Certain embodiments of the present invention will be described in the

following by way of example, with reference to the exemplifying architecture of a

third generation (3G) mobile communications system. However, it shall be appreciated

that the embodiments may be applied to any suitable communication system.

[0021] Reference is made to Figure 1 which shows an example of a network

architecture wherein the invention may be embodied. In Figure 1 an IP Multimedia Network (IMS) 45 is provided for offering IP multimedia services for IP Multimedia

Network subscribers.

[0022] As described above, IP Multimedia (IM) functionalities can be provided by

means of a mobile communication system. A mobile communication system is

typically arranged to serve a plurality of mobile user equipment (UE) usually via a

wireless interface between the user equipment and at least one base station of the

communication system. The mobile communication system may logically be divided

between a radio access network (RAN) and a core network (CN).

[0023] In the system a base station 31 is arranged to transmit signals to and receive

signals from mobile user equipment 30 of a mobile user i.e. subscriber via a wireless

interface between the user equipment and the radio access network. Correspondingly,

the mobile user equipment is able to transmit signals to and receive signals from the

radio access network via the wireless interface.

[0024] In the shown arrangement the user equipment 30 may access the IMS network

45 via the access network associated with base station 31, respectively. It shall be

appreciated that, although, for clarity reasons Figure 1 shows a base station of only

one radio access network, a typical communication network system usually includes a

number of radio access networks.

[0025] The 3G radio access network (RAN) is typically controlled by appropriate

radio network controller (RNC). This controller is not shown in order to enhance

clarity. A controller may be assigned for each base station or a controller can control a

plurality of base stations, for example in the radio access network level.. It shall thus be appreciated that the name, location and number of the network controllers depends

on the system.

[0026] The mobile user equipment 30 may comprise any appropriate mobile user

equipment adapted for Internet Protocol (IP) communication to connect the network.

For example, the mobile user may access the cellular network by means of a Personal

computer (PC), Personal Data Assistant (PDA), mobile station (MS) and so on. The

following examples are described in the context of mobile stations.

[0027] One skilled in the art is familiar with the features and operation of a typical

mobile station. Thus, it is sufficient to note that the user may use a mobile station for

tasks such as for making and receiving phone calls, for receiving and sending data

from and to the network and for experiencing multimedia content or otherwise using

multimedia services. A mobile station may include an antenna for wirelessly receiving

and transmitting signals from and to base stations of the mobile communication

network. A mobile station may also be provided with a display for displaying images

and other graphical information for the user of the mobile user equipment. Camera

means may be provided for capturing still or video images. Speaker means are also

typically provided. The operation of a mobile station may be controlled by means of an

appropriate user interface such as control buttons, voice commands and so on.

Furthermore, a mobile station is provided with a processor entity and a memory

means. [0028] It shall be appreciated that although only one mobile station is shown in Figure

1 for clarity, a number of mobile stations may be in simultaneous communication with

base stations of a mobile communication system.

[0029] The core network (CN) entities typically include various switching and other

control entities and gateways for enabling the communication via a number of radio

access networks and also for interfacing a single communication system with one or

more communication system such as with other cellular systems and/or fixed line

communication systems. In the 3 GPP systems the radio access network controller is

typically connected to an appropriate core network entity or entities such as, but not

limited to, a serving general packet radio service support node (SGSN) 33. The radio

access network controller is in communication with the serving GPRS support node

via an appropriate interface, for example on an Iu interface. Although not shown, the

SGSN typically has access to designated subscriber database configured for storing

information associated with the subscription of the respective user equipment.

[0030] The serving GPRS support node, in turn, typically communicates with a

gateway GPRS support node (GGSN) 34 via the GPRS backbone network 32. This

interface is commonly a switched packet data interface.

[0031] Figure 1 shows an application server (AS) 50. The user equipment 30 may

connect, via the GPRS network, to the application server that is connected to one or

more data networks such as, but not limited to, the exemplifying Internet Protocol (IP)

network. It shall be appreciated that a great number of application servers may be

connected to each data network. [0032] The communication systems have developed in the direction wherein services

are provided for the user equipment by means of various functions of the data network

that are handled by controller entities, such as servers. For example, in the current

third generation (3G) wireless multimedia network architectures it is assumed that

several different servers providing various control functions are used for the service

provision control. These include functions such as the call session control functions

(CSCFs). The call session functions may be divided into various categories such as a

proxy call session control function (P-CSCF), interrogating call session control

function (I-CSCF), and serving call session control function (S-CSCF). It shall be

appreciated that similar functions may be referred to in different systems with different

names. For example, in certain applications the CSCFs may be referenced to as the

call state control functions.

[0033] A user who wishes to use services provided by an application server via the

IMS system may need first to register with a serving controller, such as the serving call

session control function (S-CSCF 1) 42. As shown in Figure 1, communication

between the S-CSCF 42 and the user equipment 30 may be routed via at least one

proxy call session control function (P-CSCF) 35 and an intenOgating call session

control function I-CSCF 36. The proxy CSCF 35 is thus for proxying messages from

the GGSN 34 to a serving call session control function 42. The S-CSCF 42 in Figure

1, in turn, provides the control entity the user equipment 30 needs to be registered

with. The registration is required to enable the user equipment to request a service

from the communication system. [0034] The system of Figure 1 is further arranged such that a user who has been

provided with required communication resources by the backbone network and is

registered to the S-CSCF 42 has to initiate the use of services offered by the

application server 50 by sending a request for the desired service to the S-CSCF 42

over the communication system.

[0035] In Figure 1, another serving call session control function 43, S-CSCF2, is

illustrated. In practice there will of course be a number of S-CSCFs.

[0036] A user information storage entity may also be provided for storing subscriber

i.e. user related information. In the particular embodiment the storage entity is shown

to be provided by means of a home subscriber server (HSS) 37. The home subscriber

server (HSS) 37 can be queried by other function entities over the appropriate

interfaces, e.g. during session set-up procedures and later. The subscriber information

may include information such as data required for registration and authentication

purposes (e.g. identities and registration status of the subscriber) and so on. The HSS

37 can also be used for storing permanently subscriber profile information. In

particular, the home subscriber server holds information associating public identities

with particular user equipment UE, and identifying the S-CSCF to which that UE is

registered. Each UE is identified with unique private identity, which has the form of

Network Access Identifier, for example UEl@example.org.

[0037] Figure 2 shows by way of example the contents of the home subscriber server

database 38. It will be appreciated that this is by way of example only and the precise

layout and protocol will vary in accordance with the network requirements. Each user equipment UE may be associated with multiple public identities which are labeled

Pidl to Pid7 in Figure 2. The public identity is user's public address, which is used for

communications within the IMS system. The public user identity can, for example, be

in a form of SIP URI like sip: pidl@example.org. The public identities may be

handled individually or they can be grouped to one or several public identity sets. The

public identities may be shared by multiple UEs. Each individual public identity or a

set of public identities are registered independently by each UE sharing them and they

can have different services executed in the network. Each public identity can have a

registered or unregistered status, which is dependent on the UE, and, when registered,

is associated with a particular S-CSCF.

[0038] It is supposed to be the case that all public identities for a particular user

equipment UE should be registered with the same S-CSCF. When multiple UEs share

one or more public identities, all the public identities associated with those UEs have

to be registered to the same S-CSCF. Sometimes circumstances occur (as described

later) so that one of the public identities is registered with a different S-CSCF to the

others. The following described embodiment takes care of such a situation in a

command-efficient manner. This will now be described with reference to Figure 3.

[0039] In a 3G network, when a user first switches on his mobile terminal, he must

register his user ID or address with the network before allowing the terminal to fully

connect. This is done by sending an SIP 'REGISTER' message, which includes details

of the user's address, from the terminal to the IMS. The IMS processes this

information, via the serving call state control function (S-CSCF), storing the relevant registration information at the HSS. This registration information may include the

status of the user such as the location, terminal capability and user availability. The

registration is acknowledged by the IMS through a suitable response message that is

also in accordance with SIP. Subsequent registrations also take place ('re-

REGISTER') whenever the preceding registration has expired, or when there is a

change in the status of the user or another reason to refresh the registration.

[0040] If, in a registration procedure, the previously assigned S-CSCF does not

respond to the register message sent from the I-CSCF after a timeout, a new S-CSCF

is assigned for the user. In Figure 3, a failed registration request is shown as being

transmitted from the user equipment UEl to the first S-CSCF 1, 42. A subsequent

registration request in respect of the first public identity PID1 is shown having been

successfully made to the second S-CSCF2, 43. However, in order to request

authentication information and to inform the HSS the user equipment UEl as having

been registered in respect of S-CSCF2, the S-CSCF2 issues a Multimedia-Auth-

Request (MAR) command which identifies the second S-CSCF2. The home

subscriber server 37 receives the MAR command and, noticing that the command

includes a different S-CSCF name than the previous one which had been stored,

dispatches an RTR command towards the first S-CSCF 1 via the Cx interface. The

home subscriber server 37 inserts into the RTR command the deregistration reason

NEW_SERVER_ASSIGNED, and also inserts the public identities belonging to the

same implicitly registered set (Set 1) as the notified public identity Pidl. In this case,

it will insert Pidl, Pid2 and Pid3. The home subscriber server inserts also the private identity of the UEl into the RTR. When the first S-CSCF 1 receives the RTR command

with the deregistration reason assigned to the value NEW_SERVER_AS SIGNED it

removes the user data of those public identities which are in the request and the user

data of all other public identities, which are related to the same UEl, that is, to the

same private identity. That is, it removes Pidl - Pid6 as being associated with S-

CSCF1. It also issues a NOTIFY message to the user equipment UEl identifying the

public identities/identity sets which had a registered status and which were not

included in the RTR command, and which have now been deregistered from S-

CSCF1. The NOTIFY message contains an indication for the user equipment UEl to

re-register these public identities at the new S-CSCF2. It achieves this by performing

a re-registration procedure as indicated in Figure 3, and as described above. Note that

the public identities (Set 2) which are in an unregistered state at the first S-CSCF 1 are

removed, but no NOTIFY message is sent for those identities because there is no need

to re-register them.

[0041] When removing the public identities of the UEl, the S-CSCF detects the

shared public identity, in the example Pid6, and based on that, it removes all the user

data, which is related to the sharing UE2. That is, it removes Pid6 - Pid7 as being

associated with S-CSCF1. It also issues a NOTIFY message to the user equipment

UE2 identifying the public identities/identity sets which had a registered status and

which were not included in the RTR command, and which have now been deregistered

from S-CSCF 1. The NOTIFY message contains an indication for the user equipment

UE2 to re-register these public identities at the new S-CSCF2. It achieves this by performing a re-registration procedure as indicated in Figure 3, and as described

above. Note that the public identity 7 (Set 4) which is in an unregistered state at the

first S-CSCF 1 is removed, but no NOTIFY message is sent for that identity because

there is no need to re-register it.

[0042] The above-described embodiment of the invention thus optimises an existing

functionality of 3 GPP IMS deregistration. In particular it optimises the Cx interface

usage and the behaviour of the HSS in the deregistration procedure during the change

of the assigned S-CSCF. This is achieved in the above described embodiment by

carrying out the deregistration procedure of multiple public user identity sets and UEs

with a single RTR command during the change of the S-CSCF. The reason

NEW_SERVER_ASSIGNED indicates that the S-CSCF shall start the deregistration

procedure (i.e. issue a notify message) towards the user equipment UE for the rest of

the user's public identity/identity sets which are registered for that S-CSCF 1 and

which are not yet registered in the newly assigned S-CSCF2. Another alternative is

that a new reason value is introduced instead of using the existing reason

NEW_SERVER_ASSIGNED. This might be necessary to guarantee the interworking

between different releases of 3 GPP IMS solutions.

[0043] Thus, only a single RTR/RTA command pair needs to be processed, instead of

multiple pairs as in the existing 3G system.

[0044] It will readily be appreciated that the IMS network illustrated in Figure 1 may

comprise further S-CSCFs, interrogating CSCFs and proxy CSCFs. Likewise, although embodiments of the present invention have been described in the context of

3G using SIP, other suitable systems and interface protocols could be used.

[0045] It is also noted herein that while the above-described exemplifying

embodiments of the invention, there are several variations and modifications which

may be made to the disclosed solution without departing from the scope of the present

invention as defined in the appended claims.

Claims

CLAIMS:

1. A method of reassigning user data in a communications system, the user

data comprising a plurality of identities for each user, the method comprising the steps

of: storing in a user information store a plurality of identities in association with a

first serving controller, the plurality of identities being associated with respective

registration statuses selected from a registered status and an unregistered status; detecting that a user has requested a registration to a second serving controller

using at least one of said plurality of identities; issuing a registration termination request identifying the at least one of the

plurality of identities, which has been newly assigned to the second serving controller

as a result of the requested registration; and responsive to the registration termination request, i) issuing a re-registration

notification to the user including the at least one of the plurality of identities which has

a registered status and which was not assigned to the second serving controller as a

from the first serving controller.

2. A method according to claim 1, wherein the step of disassociating all

identities of the said user from the first serving controller comprises removing the all

identities and their data from the first serving controller, and removing their

association in the user information store with the first serving controller.

3. A method according to claim 1/ wherein the plurality of identities

include a set of unregistered statuses, and wherein the set is disassociated but not

reassigned.

4. A method according to claim 1, wherein the registration termination

request includes a deregistration reason.

5. A method according to claim 4, wherein the deregistration reason in a

3GPP communication system comprises NEW_SERVER_ASSIGNED.

6. A method according to claim 1, wherein the step of detecting that the

user has requested registration comprises receiving at the user information store an

authentication request.

7. A method according to claim 1, wherein at least two users have a shared

identity and a non-shared identity and the method further comprises a step of

checking, when the non-shared identity has been newly assigned to the second serving

controller, whether the user has the shared identity and, if so, issuing a re-registration

notification to other users sharing the shared identity.

8. A communications system comprising: a first serving controller; a user information store, which holds for a user a plurality of identities in

unregistered status; a second serving controller configured to transfer to the user information store a

user authentication request identifying the user; and wherein the user information store

is operable to detect the user authentication request and comprises means for inserting

into a registration termination request issued to the first serving controller each

identify of that user, which was newly associated to the second serving controller as a

result of the user authentication request, and wherein the first serving controller is

operable, responsive to the registration teπnination request, to i) issue a re-registration

notification to the user including each identity which has a registered status and which

was not assigned to the second serving controller as a result of the user authentication

request, and ii) disassociate all identities of the said user from the first serving

controller.

9. A communications system according to claim 8, wherein the user

information store comprises a home subscriber server.

10. A communications system according to claim 8, wherein the serving

controller comprises a call state control function.

11. A communications system according to claim 8, wherein the

communications system is wireless.

12. A communications system according to claim 8, wherein said plurality

of identities includes a shared identity which is associated with at least one other user.

13. A communications system according to claim 12, wherein the first

serving controller is operable to issue a re-registration notification to the at least one

other user.

14. A serving controller for use in a system for providing communication

between users, the serving controller having an interface adapted to communicate with

a user information store, whereby a plurality of identities, each with respective

registration statuses, associate a user with the serving controller and being operable,

responsive to a registration termination request received from the user information

store, to i) issue a re-registration notification to the user including each identity which

has a registered status and which incorrectly associates the user with the first serving

controller, and ii) disassociate all identities of the said user from the serving controller.

15. A serving controller according to claim 14, which is operable to

disassociate all identities of the said user by removing the identities and their data in

the serving controller and by removing their association in the user information store. or 5_t

16. A serving controller according to claim 14^ which is operable to read a

deregistration reason in the registration termination request.

17. A serving controller according to claim 14, which is operable to issue a

re-registration notification to any other users sharing one of the said identities.

18. A communications system, utilizing the reassignment of user data

comprising a plurality of identities for each user, the system comprising: storing means for storing in a user information store a plurality of identities in

association with a first serving controller, the plurality of identities being associated

with respective registration statuses selected from a registered status and an

unregistered status; detecting means for detecting that a user has requested a registration to a

second serving controller using at least one of said plurality of identities; issuing means for issuing a registration termination request identifying the at

least one of the plurality of identities, which has been newly assigned to the second

serving controller as a result of the requested registration; notification means for issuing a re-registration notification to the user including

the at least one of the plurality of identities which has a registered status and which

was not assigned to the second serving controller as a result of the requested

registration; and disassociating means for disassociating all identities of the said user from the

first serving controller; wherein the notification and disassociating means are responsive to the

registration termination request.

19. A system according to claim 18, wherein the disassociating means

comprises removing means for removing the all identities and their data from the first

serving controller, and removing their association in the user information store with

the first serving controller.

20. A system according to claim 18, wherein the plurality of identities

reassigned.

21. A system according to claim 18, wherein the detecting means comprises

receiving means for receiving at the user information store an authentication request.

22. A system according to claim 18, wherein at least two users have a shared

identity and a non-shared identity and the system further comprises checking means

for checking, when the non-shared identity has been newly assigned to the second

serving controller, whether the user has the shared identity and, if so, the notification

means is configured to issue a re-registration notification to other users sharing the

shared identity.