WO2017213565A1

WO2017213565A1 - Identity handling in ip multimedia subsystem

Info

Publication number: WO2017213565A1
Application number: PCT/SE2016/050563
Authority: WO
Inventors: Michele MAIORINO; Elvira Villani; Francesco TORO; Alessandro Mordacci
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2016-06-10
Filing date: 2016-06-10
Publication date: 2017-12-14

Abstract

An application server (102) in an internet protocol multimedia subsystem, IMS, generates a new SIP message (501) that notifies, e.g., a proxy call/session control function, P-CSCF (104) about the fact that the identity N1 of an originating entity (110) has been changed from N1 to N2 in SIP signaling on a terminating side (522). An advantage of this is that services, e.g. a lawful interception, LI, service, implemented in an entity in an originating leg (520), e.g. the P-CSCF (104), can make use of this change of identity information.

Description

IDENTITY HANDLING IN IP MULTIMEDIA SUBSYSTEM TECHNICAL FIELD

Embodiments herein relate to wireless communication and more specifically to handling of identities of an originating entity in an internet protocol multimedia subsystem (IMS). BACKGROUND

Wireless communication systems of today have evolved during the last decade into systems that can provide users with very high bitrate digital communication services. Needless to say, the desire of users to have access to multimedia services at all times and at any location has been a strong driver for such evolution and standardization work has produced the so-called Internet protocol Multimedia Subsystem (IMS).

IMS has introduced a change in telecommunication network in that it specifies a separation of the access network, e.g. radio access network (RAN) from service networks that provide multimedia services and by such a separation provide a plurality of different of services regardless of access technology used by the device that is used to access the services. Examples of access technologies include third generation partnership project (3GPP) wideband code division multiple access (WCDMA) as well as long term evolution (LTE) technologies and evolved variants of these, as well as other access technologies including Institute of Electrical and Electronics Engineers' (IEEE) 802.1 1 standards.

The IMS is completely based on the Internet protocol (IP) and it allows a faster introduction of new services compared to the circuit switched legacy architecture where mobile switching center (MSC) nodes control both service and access. IMS services meet flexibility, easy deployment and customization needs coming from both telecommunication operators and end-users. Services that are provided in the IMS context include voice services such as voice over IP (VoIP), video services as well as message services such as chat and short message service (SMS).

Many services in the IMS context are associated with requirements regarding user identities, for example due to the fact that many services depend on the possibility of charging users for use of the services. In addition, from a lawful interception (LI) point of view, a network operator shall provide access to intercepted content of communications (CC) and intercept related information (IRI) of mobile targets and services related to the target (e.g. call forwarding) on behalf of law enforcement agencies (LEAs). An LEA provides intercept requests (e.g., lawful authorization or warrant) to the network operator. The intercept request identifies, at a minimum, the target, the type of intercept (i.e., IRI- only, or IRI and CC) that is authorized, the authorized period for interception, and the LEA delivery address(es) for the intercepted information. Figure 1 illustrates an IMS 100 and two connected access networks in the form a RAN 1 12 and a local area network (LAN). An originating entity 1 10 is connected to the RAN 1 12 and a terminating entity 1 14 is connected to the LAN 1 16. The IMS 100 comprises a proxy call/session control function (P-CSCF) 104, a serving call/session control function (S-CSCF) 106 and an application server (AS) 102. A law enforcement agency (LEA)/law enforcement management function (LEMF) 1 18 is connected to the IMS 100. Signaling between the entities in the IMS and the connected entities takes place by means of session initiation protocol (SIP) signaling.

Figure 2 is a schematically illustrated signaling diagram involving some of the entities in figure 1 . An originating leg 220 illustrates that a SIP invite message 201 from the originating entity 1 10, having an identity N1 , is conveyed via the P-CSCF 104 and the S- CSCF 106 to the AS 102. The AS 102 changes the SIP invite message 201 by replacing the identity N1 with an identity N2 and transmits a changed SIP invite message 203 in a terminating leg 222 to the terminating entity 1 14 via the S-CSCF 106. Needless to say, various other nodes may be present along the terminating leg as illustrated by reference numeral 125 (the functionality of which is outside the scope of the present disclosure) and the broken message line 250.

There are drawbacks with such prior art solutions as is evident when reading, e.g., 3GPP standard specifications relating to SIP signaling in IMS. For example, for an IMS service where a calling identity, e.g. the identity of the originating entity 1 10, is being changed by the AS serving the originating entity, i.e. during a SIP session setup phase, neither originating entity nor other services implemented in the IMS nodes that precede the AS in the SIP signaling chain, such as for example LI, are made aware of such an identity change. It comes along that from an end user perspective the lack of notification of identity change may downgrade the user experience, whilst from an LI perspective serious legal implications will occur, i.e. no LI is activated even if the identity being changed by the AS is under monitoring. Although change of identity performed by a terminating service doesn't currently have the same issues, given the flexibility of IMS it is possible that such a service modifying the calling identity in terminating side may be developed in the future. In such a case a similar problem as for the originating case may arise.

More specifically, as far as LI is concerned, the problem with current solutions is that if the originating entity 1 10 has two associated identities, e.g. N1 and N2, and only e.g. the N2 identity is the one under monitoring in the IMS 100 domain, when a call is started from the originating entity 1 10 by using e.g. N1 identity, in the signaling leg from the originating entity 1 10 up to the AS 102 only e.g. N1 is shown as the originating identity within SIP signaling messages, whilst in the leg from the AS 102 down to the terminating entity 1 14 only e.g. N2 is shown as originating identity within SIP signaling messages. As illustrated in figure 2, this will inevitably cause lack of interception in the leg 220 from the originating entity 1 10 up to the AS 102, which in many traffic cases is the only point in an operator network where, for legal/jurisdiction limitation reasons, interception may take place. The point 299 in figure 2 on the timeline of the S-CSCF 106 represents the only available point of intercept (Pol) in the IMS 100; nevertheless, such Pol is not able to provide the CC and it is not possible (for legal/jurisdiction limitation reasons) to rely on the terminating side that is not guaranteed to provide a Pol.

It is to be noted that, while 3GPP standards specify the S-CSCF as Pol, some

implementations rely on the P-CSCF exclusively (for example because the S-CSCF is placed on a hub serving multiple countries). In those cases not even IRI is available for LI. Relevant prior art standard specifications include 3GPP technical specifications (TS) 23.228 related to SIP signalling in IMS, 33.106, 33.107 and 33.108 relating to LI.

SUMMARY

In view of the above, an object of the present disclosure is to overcome or at least mitigate at least some of the drawbacks related to handling identities in an internet protocol multimedia subsystem (IMS).

This object is achieved in a first aspect by a method performed by an application server in an IMS. The method comprises receiving a SIP invite message on an originating leg. The SIP invite message comprises a first identity, N1 , which is associated with an originating entity. A second identity, N2, is then associated with the originating entity and a modified SIP invite message is created. In the modified SIP invite message N1 is replaced by N2. The modified SIP invite message is transmitted on a terminating leg. A new SIP message is created that comprises N1 and N2 and this new SIP message is transmitted on the originating leg.

The object is achieved in a second aspect by a method performed by a proxy call/session control function in an IMS. This method comprises receiving a SIP invite message from an originating entity on an originating leg. The SIP invite message comprises a first identity, N1 , which is associated with the originating entity. The SIP invite message is transmitted to a serving call/session control function on the originating leg. A new SIP message that comprises N1 and a second identity, N2, is received and a specific service is executed that utilizes at least one of the received identities N1 and N2. In other words, a new SIP message is introduced, generated by the AS, to notify at least one entity in the originating leg, for example a P-CSCF or even the originating entity, about the fact that the identity N1 of the originating entity has been changed from N1 to N2 in SIP signaling on the terminating side. An advantage of this is that services implemented in an entity in the originating leg, e.g. the P-CSCF, can make use of this change of identity information. As will be exemplified below, one such service that can make use of the information may be a lawful interception (LI) service.

In some embodiments, the creation of the new SIP message that comprises N1 and N2 comprises storing (by the AS) and reading (by the P-CSCF) any of N1 and N2 in a History-Info information field of the new SIP message. In some of these embodiments, an appropriate value may be stored in (and read in) a privacy header field such that N1 and N2 is visible only to at least one intermediate entity between the AS and the originating entity, excluding the originating entity, in the originating leg.

In some embodiments, supplementary information related to any of N1 and N2 may be stored in and read in any of a reason phrase, a header field and a message body of the new SIP message.

The execution, in the P-CSCF, of the specific service may in various embodiments be triggered by the reception of the new SIP message that comprises N1 and N2.

As indicated, embodiments include those wherein the specific service may be a LI service and that the LI service is related to N2 and is requested from a law enforcement agency, (LEA). In some embodiments, the new SIP message that comprises N1 and N2 may be transmitted to the originating entity.

In another aspect there is provided an application server, AS, for an internet protocol multimedia subsystem, IMS. The AS comprises input/output circuitry, a processor and a memory. The memory contains instructions executable by the processor whereby the AS is operative to:

- receive a session initiation protocol, SIP, invite message on an originating leg, said SIP invite message comprising a first identity, N1 , which is associated with an originating entity,

- associate a second identity, N2, with the originating entity,

- create a modified SIP invite message in which modified SIP invite message N1 is replaced by N2,

- transmit, on a terminating leg, said modified SIP invite message,

- create a new SIP message that comprises N1 and N2, and

- transmit, on said originating leg, said new SIP message.

In another aspect there is provided a proxy call/session control function, P-CSCF, for an internet protocol multimedia subsystem, IMS. The P-CSCF comprises input/output circuitry, a processor and a memory. The memory contains instructions executable by the processor whereby the P-CSCF is operative to:

- receive a session initiation protocol, SIP, invite message from an originating entity on an originating leg, said SIP invite message comprising a first identity, N1 , that is associated with the originating entity,

- transmit, to a serving call/session control function, S-CSCF, on said originating leg, said SIP invite message,

- receive a new SIP message that comprises N1 and a second identity, N2, and

- execute a specific service that utilizes at least one of the received identities N1 and

N2.

In another aspect there is provided a computer program comprising instructions which, when executed on at least one processor in an application server, AS, for an internet protocol multimedia subsystem, IMS, cause the AS to carry out the method according to the first aspect summarized above.

In another aspect there is provided a computer program comprising instructions which, when executed on at least one processor in a call/session control function, P-CSCF, for an internet protocol multimedia subsystem, IMS, cause the P-CSCF to carry out the method according to the second aspect summarized above.

In further aspects there are provided carriers comprising any of the computer programs summarized above, wherein the carrier is one of an electronic signal, an optical signal, a radio signal and a computer readable storage medium.

These other aspects provide the same effects and advantages as summarized above in connection with the methods of the first and second aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematically illustrated block diagram of an IMS,

figure 2 is a prior art signaling diagram,

figures 3 and 4 are flowcharts illustrating embodiments of methods,

figure 5 is a signaling diagram,

figure 6 schematically illustrates an application server,

figure 7 schematically illustrates an application server,

figure 8 schematically illustrates a proxy call/session control function, and

figure 9 schematically illustrates a proxy call/session control function.

DETAILED DESCRIPTION

Embodiments of methods performed by an AS and embodiments of methods performed by a P-CSCF in an IMS will now be described in some more detail with reference to figures 3, 4 and 5 and with continued reference to figure 1 , remembering that figure 1 illustrates an IMS 100.

As mentioned above, the IMS 100 is connected to two access networks in the form a RAN 1 12 and a local area network (LAN) that may include a wireless LAN 1 16 that operates according to, e.g. an IEEE 802.1 1 standard. The access networks 1 12, 1 16 are connected to the IMS 100 via interface functionality 121 , 123 in appropriate gateway nodes that are not illustrated in figure 1 . An originating entity 1 10 is connected via an air interface 1 1 1 to the RAN 1 12 and a terminating entity 1 14 is connected to the LAN 1 16 via an appropriate connection interface 1 15. The IMS 100 comprises a proxy call/session control function (P- CSCF) 104, a serving call/session control function (S-CSCF) 106 and an application server (AS) 102. A law enforcement agency (LEA) 1 18 is connected to the IMS 100 via an appropriate connection interface 125. Signaling between the entities in the IMS and the connected entities takes place by means of session initiation protocol (SIP) signaling. It is to be noted that functionality indicated by reference numerals 121 , 123 and 125 are outside the scope of the present disclosure.

It is also to be noted that, although figure 1 illustrates a single AS 102, a single P-CSCF 5 104 and a single S-CSCF 106, typical implementations of an IMS may in various

embodiments include a larger number of these entities. Moreover, although figure 1 illustrates the AS 102, the P-CSCF 104 and the S-CSCF 106 as separate blocks, typical implementations may in some embodiments realize these entities in a larger and more general processing system, e.g. in the form of one or more computer servers (e.g. a so-0 called cloud implementation) having functional blocks that operate to realize functionality of the AS, the P-CSCF and the S-CSCF.

Now with reference to figure 3 and figure 5, a method performed by the AS 102 in the IMS 100 will be described by way of a number of actions as follows.

Action 302

5 A SIP invite message 501 is received on an originating leg 520. This SIP invite message comprises a first identity, N1 , which is associated with the originating entity 1 10.

As the skilled person will realize, N1 is typically carried in a "From" header field in the SIP invite message.

Action 304

0 A second identity N2 is associated with the originating entity.

In other words, this action may be seen as the AS changing the identity N1 to the new identity N2. Such a change may, as the skilled person will realize, be part of, e.g., a service such as a flexible identity presentation (FIP) service that the AS performs on behalf of the originating entity. 5 Action 306

A modified SIP invite message 503 is then created in which N1 is replaced by N2.

As the skilled person will realize, the AS may perform further changes and/or additions in the modified SIP invite message 503, but these are outside the scope of the present disclosure. Action 308

The modified SIP invite message 503 is then transmitted on a terminating leg 522. As exemplified in figure 5, this modified SIP invite message 503 may reach the terminating entity via the S-CSCF 106 and various other entities as indicated by the broken message line 550.

Action 310

A new SIP message 505 is created that comprises N1 and N2.

For example, in various embodiments any of N1 and N2 may be stored in a History-Info information field of the new SIP message. Also, in various embodiments, the creation of the new SIP message 505 may comprise storing an appropriate value in a privacy header field. This will mean that N1 and N2 is visible only to at least one intermediate entity between the AS and the originating entity, excluding the originating entity, in the originating leg.

Supplementary information related to any of N1 and N2 may also be stored in the new SIP message 505. The storing of such supplementary information may be in any of a reason phrase, a header field and a message body of the new SIP message 505.

Examples of supplementary information include informative text that, e.g., can indicate what the service has done with any of N1 and N2.

It is to be noted that although this creating action is described subsequent to creating and transmitting actions 306 and 308, it may be performed prior to or concurrent with any one or both of these actions 306 and 308.

Action 312

The new SIP message 505 is then transmitted on the originating leg 520.

Now with reference to figure 4 and with continued reference to figure 5, a method performed by the P-CSCF 104 in the IMS 100 will be described by way of a number of actions as follows. As the skilled person will realize, the actions are performed in connection with the actions performed by the AS, described above, as illustrated by the progress of time in figure 5.

Action 402

The SIP invite message 501 is received from the originating entity 1 10 on the originating leg 520. The SIP invite message 501 comprises a first identity, N1 , which is associated with the originating entity 1 10.

Action 404

The SIP invite message 501 is then transmitted to the S-CSCF 106 on the originating leg 5 520.

Action 406

A new SIP message 505 that comprises N1 and a second identity, N2, is received

Embodiments include those where any of N1 and N2 is read from a History-Info information field of the new SIP message, as illustrated by an action 4061 . 0 Embodiments include also those where the reading action 4061 comprises reading a value in a privacy header field (in the new SIP message 505) such that N1 and N2 is visible only to at least one intermediate entity between the AS 102 and the originating entity 1 10, excluding the originating entity 1 10, in the originating leg 520.

Example embodiments include also those where the reading action 4061 comprises5 reading supplementary information related to any of N1 and N2 in any of a reason phrase, a header field and a message body of the new SIP message 505.

Action 408

0 A specific service that utilizes at least one of the received identities N1 and N2 is

executed.

For example, the execution of the specific service may in fact be triggered by the reception of the new SIP message 505.

Example embodiments include those where the specific service that is executed by the P-5 CSCF 104 is a lawful interception, LI, service requested from a law enforcement Agency (LEA) 1 18, the LI service being related to N2. Such a request from the LEA 1 18 is exemplified by action 4062. It is to be noted that an actual time of reception of such a LI service activation request may occur at any time, for example at a time that is prior the timing of messages illustrated in figure 5. Action 410

In some embodiments, the new SIP message that comprises N1 and N2 is then transmitted to the originating entity 1 10.

That is, transmission of the new SIP message 505 to the originating entity 1 10 is optional, since it may have been decided that the originating entity 1 10 is not to be allowed to have knowledge about the change of identity from N1 to N2 in the terminating leg 522. It is to be noted, however, that, even if the transmission in action 410 takes place, the originating entity 1 10 may be prevented knowledge of N2 by way of the use of the privacy header field, as described above. Various actions as described above may be combined into an exemplifying scenario as follows:

A call is set up by the SIP invite message 501 that originates at the originating entity 1 10. The SIP invite message 501 carries "From=N 1", which is propagated throughout the originating leg 220 up to the AS 102. The service (such as a FIP service) invoked in the AS 102 changes the "From" value to N2 and propagates the SIP invite message 503 carrying "From=N2" in the terminating leg 522. The S-CSCF 106 receiving the SIP invite message 501 carrying "From=N2" starts interception in the terminating leg 522. This interception has been triggered, as the skilled person will realize, for example by way of a request from the LEA 1 18. At the same time the AS 102 generates the new SIP message 505, which is propagated back to the originating leg 520 by carrying both N1 and the new N2 identities within the "History-Info" field. Optionally, the Reason-Phrase, other header fields or the message body may be used to convey more details about the call progress.

Both S-CSCF 106 and the P-CSCF 104 receives the new SIP message 505, but only the P-CSCF 104 reacts on it by starting mid-call interception as the SIP call set-up is already ongoing. The P-CSCF 104 has been triggered due to the fact that N2 is the target (i.e. the monitored identity) as indicated by the LEA 1 18.

The IRI provided by the S-CSCF 106 and the P-CSCF 104 is, as the skilled person will realize, correlated by a LI mediation device (not shown in the figures) based on a P- charging-vector, i.e. SIP signalling as intercepted by both the P-CSCF 104 and the S- CSCF 106 contain the same value. Similarly, the CC provided by the P-CSCF 104 is correlated by LI mediation with IRI as in design base, i.e. correlation between CC and IRI is unchanged and follows relevant standard specifications, e.g.3GPP as well as European Telecommunications Standards Institute (ETSI) standards and American National Standards Institute (ANSI) standards. The new SIP message 505, as propagated to the originating entity 1 10 will make the user aware about the executed AS service. However, this step of propagation to the originating entity 1 10 is optional. The notification to the originating entity 1 10 may not be needed or even confusing for certain services, or may not be supported by certain communication terminals that a user may have. Propagation of the new SIP message 505 to the originating entity 1 10 is therefore optional. Preventing the new SIP message 505 to reach the originating entity 1 10 is possible using current IMS and SIP standards, for example the AS 102 may include a privacy header in the new SIP message 505 with value "history". Such a privacy header will limit the visibility of the history-list. Alternatively, the P-CSCF 104 may be configured to not forward the history-list and/or the new SIP message 505 to the originating entity 1 10. Alternatively, the P-CSCF 104 may implement any service logic to process the header of the new SIP message 505 and the P-CSCF 104 may use any supplementary information, such as reason phrase, header field etc. for services other than LI.

Turning now to figure 6, a schematically illustrated AS 600 will be described in some more detail. The AS 600 is for an IMS. The AS 600 comprises input/output circuitry 606, a processor 602 and a memory 604. The memory 604 contains instructions executable by the processor 602 whereby the AS 600 is operative to:

- receive a session initiation protocol, SIP, invite message 501 on an originating leg 520, said SIP invite message 501 comprising a first identity, N1 , which is associated with an originating entity 1 10,

- associate a second identity, N2, with the originating entity 1 10,

- create a modified SIP invite message 503 in which modified SIP invite message 503 N1 is replaced by N2,

- transmit, on a terminating leg 522, said modified SIP invite message 503,

- create a new SIP message 505 that comprises N1 and N2, and

- transmit, on said originating leg 520, said new SIP message 505.

The instructions that are executable by the processor 602 may be software in the form of a computer program 641 . The computer program 641 may be contained in or by a carrier 642, which may provide the computer program 641 to the memory 604 and processor 602. The carrier 642 may be in any suitable form including an electronic signal, an optical signal, a radio signal or a computer readable storage medium.

In some embodiments, the application server is operative such that the creation of the new SIP message that comprises N1 and N2 comprises storing any of N1 and N2 in a History-Info information field of the new SIP message.

In some embodiments, the application server is operative such that the creation of the new SIP message that comprises N1 and N2 comprises storing an appropriate value in a privacy header field such that N1 and N2 is visible only to at least one intermediate entity between the AS and the originating entity, excluding the originating entity, in the originating leg.

In some embodiments, the application server is operative such that the creation of the new SIP message that comprises N1 and N2 comprises storing supplementary information related to any of N1 and N2 in any of a reason phrase, a header field and a message body of the new SIP message.

Figure 7, illustrates schematically an application server 700 that comprises:

- a receiving module 702 configured to receive a session initiation protocol, SIP, invite message 501 on an originating leg 520, said SIP invite message 501 comprising a first identity, N1 , which is associated with an originating entity 1 10,

- an associating module 704 configured to associate a second identity, N2, with the originating entity 1 10,

- a creating module 706 configured to create a modified SIP invite message 503 in which modified SIP invite message 503 N1 is replaced by N2,

- a transmitting module 708 configured to transmit, on a terminating leg 522, said modified SIP invite message 503,

- a creating module 710 configured to create a new SIP message 505 that comprises N1 and N2, and

- a transmitting module 712 configured to transmit, on said originating leg 520, said new SIP message 505. The application server 700 may comprise further modules that are configured to perform in a similar manner as, e.g., the application server 600 described above in connection with figure 6. Turning now to figure 8, a schematically illustrated P-CSCF 800 will be described in some more detail. The P-CSCF 800 is for an IMS. The P-CSCF 800 comprises input/output circuitry 806, a processor 802 and a memory 804. The memory 804 contains instructions executable by the processor 802 whereby the P-CSCF 800 is operative to:

5 - receive a session initiation protocol, SIP, invite message 501 from an originating entity 1 10 on an originating leg 520, said SIP invite message 501 comprising a first identity, N1 , that is associated with the originating entity 1 10,

- transmit, to a serving call/session control function, S-CSCF 106, on said originating leg 520, said SIP invite message 501 ,

10 - receive a new SIP message 505 that comprises N1 and a second identity, N2, and

N2.

The instructions that are executable by the processor 802 may be software in the form of a computer program 841 . The computer program 841 may be contained in or by a carrier 15 842, which may provide the computer program 841 to the memory 804 and processor 802. The carrier 842 may be in any suitable form including an electronic signal, an optical signal, a radio signal or a computer readable storage medium.

In some embodiments, the P-CSCF 800 is operative such that the execution of the specific service is triggered by the reception of the new SIP message that comprises N1 20 and N2.

In some embodiments, the P-CSCF 800 is operative such that the specific service is a lawful interception, LI, service requested from a law enforcement agency, LEA, the LI service being related to N2.

In some embodiments, the P-CSCF 800 is operative to read any of N1 and N2 from a 25 History-Info information field of the new SIP message.

In some embodiments, the P-CSCF 800 is operative to read a value in a privacy header field such that N1 and N2 is visible only to at least one intermediate entity between the AS and the originating entity, excluding the originating entity, in the originating leg.

In some embodiments, the P-CSCF 800 is operative to read supplementary information 30 related to any of N1 and N2 in any of a reason phrase, a header field and a message body of the new SIP message. In some embodiments, the P-CSCF 800 is operative to transmit the new SIP message that comprises N1 and N2 to the originating entity.

Figure 9, illustrates schematically an proxy call/session control function 900 that comprises:

- a receiving module 902 configured to receive a session initiation protocol, SIP, invite message 501 from an originating entity 1 10 on an originating leg 520, said SIP invite message 501 comprising a first identity, N1 , that is associated with the originating entity 1 10,

- a transmitting module 904 configured to transmit, to a serving call/session control function, S-CSCF 106, on said originating leg 520, said SIP invite message 501 ,

- a receiving module 906 configured to receive a new SIP message 505 that comprises N1 and a second identity, N2, and

- an executing module 908 configured to execute a specific service that utilizes at least one of the received identities N1 and N2. The proxy call/session control function 900 may comprise further modules that are configured to perform in a similar manner as, e.g., the proxy call/session control function 800 described above in connection with figure 8.

Claims

1 . A method performed by an application server, AS, (102, 600, 700) in an internet protocol multimedia subsystem, IMS, (100) the method comprising:

- receiving (302) a session initiation protocol, SIP, invite message (501 ) on an originating leg (520), said SIP invite message comprising a first identity, N1 , which is associated with an originating entity (1 10),

- associating (304) a second identity, N2, with the originating entity,

- creating (306) a modified SIP invite message (503) in which modified SIP invite message N1 is replaced by N2,

- transmitting (308), on a terminating leg (522), said modified SIP invite message,

- creating (310) a new SIP message (505) that comprises N1 and N2, and

- transmitting (312), on said originating leg, said new SIP message.

2. The method of claim 1 , wherein said creation of said new SIP message that comprises N1 and N2 comprises storing any of N1 and N2 in a History-Info information field of the new SIP message.

3. The method of claim 2, wherein said creation of said new SIP message that comprises N1 and N2 comprises storing an appropriate value in a privacy header field such that N1 and N2 is visible only to at least one intermediate entity between the AS and the originating entity, excluding the originating entity, in the originating leg.

4. The method of any of claims 1 to 3, wherein said creation of said new SIP message that comprises N1 and N2 comprises storing supplementary information related to any of N1 and N2 in any of a reason phrase, a header field and a message body of the new SIP message.

5. A method performed by a proxy call/session control function, P-CSCF, (104, 800, 900) in an internet protocol multimedia subsystem, IMS, (100) the method comprising: - receiving (402) a session initiation protocol, SIP, invite message (501 ) from an originating entity (1 10) on an originating leg (520), said SIP invite message comprising a first identity, N1 , that is associated with the originating entity,

- transmitting (404), to a serving call/session control function, S-CSCF, (106) on said originating leg, said SIP invite message,

- receiving (406) a new SIP message (505) that comprises N1 and a second identity, N2, and

- executing (408) a specific service that utilizes at least one of the received identities N1 and N2.

6. The method of claim 5, wherein said execution of the specific service is triggered by the reception of said new SIP message that comprises N1 and N2.

7. The method of claim 5 or claim 6, wherein said specific service is a lawful interception, LI, service requested (4062) from a law enforcement agency, LEA (1 18), said LI service being related to N2.

8. The method of any of claims 5 to 7, comprising:

- reading (4061 ) any of N1 and N2 from a History-Info information field of the new SIP message.

9. The method of claim 8, comprising reading (4061 ) a value in a privacy header field such that N1 and N2 is visible only to at least one intermediate entity between the AS and the originating entity, excluding the originating entity, in the originating leg.

10. The method of any of claims 5 to 9, comprising reading (4061 ) supplementary information related to any of N1 and N2 in any of a reason phrase, a header field and a message body of the new SIP message.

1 1 . The method of any of claims 5 to 10, comprising:

- transmitting (410) said new SIP message that comprises N1 and N2 to the originating entity.

12. An application server, AS, (102, 600) for an internet protocol multimedia subsystem, 5 IMS, (100), the AS comprising input/output circuitry (606), a processor (602) and a memory (604), said memory containing instructions executable by said processor whereby the AS is operative to:

- receive a session initiation protocol, SIP, invite message (501 ) on an originating leg (520), said SIP invite message comprising a first identity, N1 , which is associated with

10 an originating entity (1 10),

- associate a second identity, N2, with the originating entity,

- create a modified SIP invite message (503) in which modified SIP invite message N1 is replaced by N2,

- transmit, on a terminating leg (522), said modified SIP invite message, 15 - create a new SIP message (505) that comprises N1 and N2, and

- transmit, on said originating leg, said new SIP message.

13. The application server of claim 12, operative such that said creation of said new SIP message that comprises N1 and N2 comprises storing any of N1 and N2 in a History-Info information field of the new SIP message.

20 14. The application server of claim 13, operative such that said creation of said new SIP message that comprises N1 and N2 comprises storing an appropriate value in a privacy header field such that N1 and N2 is visible only to at least one intermediate entity between the AS and the originating entity, excluding the originating entity, in the originating leg.

15. The application server of any of claims 12 to 14, operative such that said creation of 25 said new SIP message that comprises N1 and N2 comprises storing supplementary information related to any of N1 and N2 in any of a reason phrase, a header field and a message body of the new SIP message.

16. A proxy call/session control function, P-CSCF, (104, 800) for an internet protocol multimedia subsystem, IMS, (100) the comprising input/output circuitry (806), a processor (802) and a memory (804), said memory containing instructions executable by said processor whereby the P-CSCF is operative to:

- receive a session initiation protocol, SIP, invite message (501 ) from an originating entity (1 10) on an originating leg (520), said SIP invite message comprising a first identity, N1 , that is associated with the originating entity,

- transmit, to a serving call/session control function, S-CSCF, (106) on said originating leg, said SIP invite message,

- receive a new SIP message (505) that comprises N1 and a second identity, N2, and

- execute a specific service that utilizes at least one of the received identities N1 and N2.

17. The proxy call/session control function of claim 16, operative such that said execution of the specific service is triggered by the reception of said new SIP message that comprises N1 and N2.

18. The proxy call/session control function of claim 16 or claim 17, operative such that said specific service is a lawful interception, LI, service requested from a law enforcement agency, LEA (1 18), said LI service being related to N2.

19. The proxy call/session control function of any of claims 16 to 18, operative to:

- read any of N1 and N2 from a History-Info information field of the new SIP message.

20. The proxy call/session control function of claim 19, operative to read a value in a privacy header field such that N1 and N2 is visible only to at least one intermediate entity between the AS and the originating entity, excluding the originating entity, in the originating leg.

5 21 . The proxy call/session control function of any of claims 16 to 20, operative to read supplementary information related to any of N1 and N2 in any of a reason phrase, a header field and a message body of the new SIP message.

22. The proxy call/session control function of any of claims 16 to 21 , operative to:

- transmit said new SIP message that comprises N1 and N2 to the originating

10 entity.

23. A computer program (641 ) comprising instructions which, when executed on at least one processor (602) in an application server (102, 600), AS, for an internet protocol multimedia subsystem, IMS, (100), cause the AS to carry out the method according to any one of claims 1 to 4.

15 24. A computer program (841 ) comprising instructions which, when executed on at least one processor (802) in a call/session control function, P-CSCF, (104, 800), for an internet protocol multimedia subsystem, IMS, (100), cause the P-CSCF to carry out the method according to any one of claims 5 to 1 1 .

25. A carrier (642, 842), comprising the computer program of any of claims 23 or 24, 20 wherein the carrier is one of an electronic signal, an optical signal, a radio signal and a computer readable storage medium.