Title of Invention	CHARGING MECHANISMS FOR IP MULTIMEDIA SERVICES
Abstract	A method of reserving credit for a mobile subscriber in respect of an IP multimedia service. The method comprises, following initial registration of the subscriber to the IP Multimedia service but prior to invocation of an IP Multimedia service, using the early session establishment procedure to reserve a credit amount at a charging control node and to notify an IP Multimedia Serving Element of the credit reservation, whereupon, at invocation of said IP multimedia service, the IP Multimedia Serving Element is able to proceed immediately with the session establishment.

Title of Invention

CHARGING MECHANISMS FOR IP MULTIMEDIA SERVICES

Abstract

A method of reserving credit for a mobile subscriber in respect of an IP multimedia service. The method comprises, following initial registration of the subscriber to the IP Multimedia service but prior to invocation of an IP Multimedia service, using the early session establishment procedure to reserve a credit amount at a charging control node and to notify an IP Multimedia Serving Element of the credit reservation, whereupon, at invocation of said IP multimedia service, the IP Multimedia Serving Element is able to proceed immediately with the session establishment.

Full Text	FORM 2 THE PATENTS ACT, 1970 (39 of 1970) & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION (See section 10, rule 13) “CHARGING MECHANISMS FOR IP MULTIMEDIA SERVICES" TELEFONAKTIEBOLAGET LM ERICSSON (PUBL), a company duly organized and existing under the laws of Sweden of SE-164 83 Stockholm, Sweden The following specification particularly describes the invention and the manner in which it is to be performed. 2 Charging Mechanisms for IP Multimedia Services Field of the Invention 5 The present invention relates to charging mechanisms for IP Multimedia services and which are applicable in particular, though not necessarily, to Push-to-talk over Cellular services. 10 Background to the Invention IP Multimedia services provide a dynamic combination of voice, video, messaging, data, etc within the same session. By growing the numbers of basic applications and the media that it is possible to combine, the number of 15 services offered to the end users win grow exponentially, and the inter-personal communication experience will be enriched. This will lead to a new generation of personalized, richer multimedia communication services. IP Multimedia Subsystem (IMS) is the technology defined by the Third 20 Generation Partnership Project (3GPP) to provide IP Multimedia services over 3G mobile communication networks. IMS provides key features to enrich the end-user person-to-person communication experience through the integration and interaction of services. IMS allows new rich person-to-person (client-to-client) as well as person-to-content (client-to--server) communications over an 25 IP-based network. The IMS makes use of the Session Initiation Protocol (SIP) and Service Delivery Protocol (SDP) to set up and control calls or sessions between user terminals (or user terminals and web servers). Figure 1 illustrates schematically how the IMS fits into the mobile network architecture. 30 Existing cellular telephone network operators have recently experienced tremendous growth in the numbers of subscribers choosing to use so-called "prepaid" subscriptions; that is where subscribers deposit an amount of cash (the credit balance) with their operators, which is consumed by tte subsequent 3 use of services by the subscribers. It is anticipated that the prepaid subscription option will prove equally popular with the users of IPMM services. Indeed, the provision of pre-paid services is likely to be a must for widespread take-up of IPMM services. When online/readme charging mechanisms are used (as for prepaid users), the general rule would be for the IPMM Serving Element (SE) providing access to the requested service, to request credit authorisation before granting a mobile node access to the requested service. However, this would inevitably 10 increase the session set-up time for prepaid subscribers, as the IPMM SE must conduct a credit authorization transaction with a Charging Control Node, also referred to as a Prepaid System (PPS) or Online Charging System (OCS). For some IPMM/IMS based services the session set-up time is critical. This 15 applies for example to so-called Push-to-talk over Cellular (PoC) services such as Instant Personal Talk and Ad-hoc Instant Group Talk, where the originating party pushes the PoC button on his/her terminal to invite one or more users to a walkie-talkie type session, and expects to be immediately in contact with the invited party/parties (as opposed to the traditional call, ring, answer based 20 telephony services). The introduction of the prepaid payment mechanism as currently proposed is likely to result in a degradation of the PoC session set-up time to an unacceptable level, or may lead to a sub-optimal user experience due to the additional delay produced by the credit authorisation phase. 25 Summary of the Invention It is an object of the invention to obviate the effects of prepaid payment mechanisms on actual and perceived subscriber service levels. 30 According to a first aspect of the present invention there is provided a method of reserving credit for a mobile subscriber in respect of an IP Multimedia service, the method comprising: following initial registration of the subscriber to the IP Multimedia 4 service but prior to invocation of an IP Multimedia service, using the early session establishment procedure to reserve a credit amount at a charging control node and to notify an IP Multimedia Serving Element of the credit reservation, 5 whereupon, at invocation of said IP Multimedia service, the IP Multimedia Serving Element is able to proceed immediately with the session connection. It will be appreciated that the early session establishment procedure will 10 comprise an exchange of appropriate messages between the IP Multimedia Serving Element and the charging control node. The messages may satisfy the requirements of the DIAMETER protocol. The early session establishment procedure will also typicaly be used for service negotiation purposes (e.g. exchange of media address and codec types) between the subscriber's terminal (UE) and the IMS Server. The early session establishment procedure may be triggered automatically following registration of the subscriber to the IP multimedia service, or may be 20 triggered, for example, by the subscriber/end-user activating a particular IP Multimedia service at his/her terminal. The invention is applicable in particular, though not necessarily, to Push-to-talk over Cellular (PoC) IP Multimedia services. The method may comprise, at one of the IP Multimedia Serving element and the charging control node, estimating an amount of credit appropriate to the IP Multimedia service. Preferably, this estimate is carried out at the charging control node. 30 In the case of a prepaid subscriber, said changing control rote will be a prepaid system (PPS) server boated h the subscriber's home network. 5 Preferably, the method comprises, at invocation of the IP Multimedia service, performing a credit authorisation procedure between the IP Multimedia Service Element and the charging control node based upon the actual service that has been requested/invoked to establish a revised credit amount The estimated credit amount Is replaced by the revised credit amount According to a second aspect of the present invention there is provided a method of operating an IP Multimedia Serving Element arranged to facilitate access to an IP Multimedia service by mobile subscribers, the method 10 comprising: following initial registration of a subscriber to the IP multimedia service but prior to initiation of the IP multimedia session, initiating an early session establishment procedure with a charging control node to reserve a credit amount at the charging control node. 15 According to a third aspect of the present invention there b provided a method of operating a charging control node arranged to control subscriber access to IP Multimedia services, the method comprising: participating in an early session establishment procedure following 20 initial registration of a subscriber to the IP Multimedia service but prior to invocation of the IP multimedia service, the charging control node estimating an appropriate credit amount to be reserved for a future session. Brief Description of the Drawings 25 Figure 1 illustrates schematically a mobile network architecture incorporating an IP Multimedia Subsystem; Figure 2 illustrates a simplified logical online charging architecture for an IPMM services; 30 Figure 3 shows the PoC Release 2 architecture; Figure 4 shows signalling associated with the early session establishment procedure for PoC Instant Personal Talk and Figures 5 and 6 show signaling associated with tie session connection 6 procedure, following early session establishment, when the service is actually invoked. Detailed Description of Certain Embodiments of the Invention In an IP Multimedia Subsystem (IMS) session there can be a number of users that are subscribers of several different IMS operators. In any generally applicable charging procedure, each of the IMS operators should be able to charge their own subscribers independently, according to their own charging policy. That is to say that different charging models may be applied in different networks for the same IMS session. Moreover, different charging models may be applied to different sets of subscribers for the same IPMM service/feature, within a given operator's network. 15 According to 3GPPRSTS 32325 and TS 32.200 and ETFDCC(Internet draft "Diameter Credit control application), two scenarios for IMS online charging are 1) "One-Time Event with Direct Debiting* scenario. "Immediate Event Charging^' modelin3GPP. "Credit Authorization with Direct Debiting" model in IETF DCC. 20 2) "Session-based Credit Control" scenario. "Event Charging with Unit Reservation" model in 3GPP. "Credit Authorization with Money Reservation" model in IETF DCC. In both models the IPMM Serving Elements (IPMM SE), i.e. credit control dent, request credit authorization from the Online Charging System (OCS)Prepaid 25 System (PPS), i.e. the credit control server, prior to allowing any service to be delivered to the end user. The Session-based Credit Control scenario is considered to be more appropriate for most IPMM services, and it is the scenario considered here. 30 Session-based Credit Control is a process in which the PPS rates a request from, a IPMM SE, reserves a suitable amount of money from the user's account, and notifies the IPMM SE of the corresponding amount of credit resources Of course, "credit resource" may not imply actual monetary credit 7 may be granted in the form of units (e.g. data volume or time) to be metered. Upon reception of a successful credit authorisation answer with a certain amount of credit resources, the IPMM SE allows service delivery to the end user and starts monitoring the usage of the granted resources. When the credit resources granted to the end user have been consumed or the service has been successfully delivered or terminated, the IPMM SE reports back to the PPS the used amount, and the PPS deducts the used amount from the user's account (the PPS may perform rating and make a new credit reservation if the service delivery is continuing). This process includes first interrogation, 10 possible intermediate interrogations, and a final interrogation. Both IPMM SE and PPS are required to maintain credit control session state information. The upper diagram of Figure 2 illustrates a general online charging architecture for IPMM, whilst the lower diagram lustrates a simplified architecture for PoC. 15 The Online Charging System (OCS) Prepaid System (PPS) provides the charging control function for a real-time charging mechanism. The Prepaid System includes the Account Balance Manager and the User Accounts, the Rating Engine and the Tariff Information. The Rating Engine provides rating values for sessions/services or events not priced at source, i.e. for which 20 serving elements do not have a price. For online charging, the IPMM SEs which may provide charging input to the PPS, are the Serving-Call Session Control Function (S-CSCF), the Multimedia Resource Function Control (MRFC), and the Application Server (AS). For Push -to-talk over Cellular (PoC) the SE providing charging input to the PPS is the PoC Server (which embraces MRF 25 and AS functionality). The interlace between the IPMM SEs and the PPS is based on the Diameter Base Protocol (DBP) and the Diameter Credit Control Application (DCC) as is being defined by 3GPP in Release 5 and 6. Figure 3 shows the PoC Release 2 architecture, where the PoC functional 30 entities are drawn with solid lines. The following interfaces are shown in Figure 3: It Floor control and media In: Floor control and media Is: PoC client to proxies session signalling If: Proxy to PoC server session signalling In: Proxy to proxy session signalling Im: Group management server to PoC client 5 Ik: Group management server to PoC server to: OTAP server to PoC cBent The PoC architecture has two PoC Server functions, Controlling PoC Server function/logical entity and Participating PoC Server function/logical entity. In 10 each PoC talk session there is only one Controiing PoC Server, whereas there can be one or more Participating PoC Server. The Controlling PoC Server handles the centralized tasks that should not be handled by more than one PoC Server in the PoC talk session. A PoC Server behaves as either a Controlling PoC Server or a Participating PoC Server, as selected on a per PoC talk 15 session basis. A PoC Server realisation (Le. physical entity/node) may behave as both a Controlling PoC Server and a Participating PoC Server at the same time and for the same PoC talk session. In the case of Instant Personal Talk and Ad-hoc 20 Instant Group TaHc, the PoC Server of the inviting user is the Controlling PoC Server. In case of Chat Group Talc and Instant Group Talk, the Controlling PoC Server is the PoC Server owning/hosting the group identity (the Global Group Identity). Further details of these PoC services are given in the Appendix below. 25 As has been outlined above, the conventional approach to credit reservation for PoC sessions is likely to result in significant session set-up delays. An alternative method of reserving credit for PoC delay sensitive services/features (Le. Instant Personal Talk and Ad-hoc Instant Group Talk) is proposed here 30 which maintains all prepaid characteristics (i.e. operator credit control, end-user real-time spending control). This method makes use of the so-called "early session” establishment procedure to reverse credit for PoC features with session set-up time before fie end-user initiates a talk session, i.e before the 9 actual PoC feature is invoked. The early session establishment procedure is used for service negotiation purposes (e.g. communication of IP address/port number for RTP/RTCP, and codec types) between the UE and his/her home PoC Server. The early session may be established immediately following IMS registration or at any later point in time. The early session establishment procedure is defined in the PoC Release 2.0 architecture. At early session establishment, the PoC Sever performs credit-reservation towards the PPS (by sending a Diameter Accounting Request (ACR), with 10 Accounting-Record-Type = START), before continuing with the processing of the early session establishment request The PPS tentatively rates the service (at this stage it is unknown which PoC feature be invoked by the user at a later time) and, if the user's credit balance is sufficient, the PPS reserves a suitable amount of money from the user's account and returns the 15 corresponding amount of credit units to the PoC Sever fm a Diameter ACA message, with Accounting-Record-Type = START). Upon successful credit reservation, the PoC Server continues processing the early session establishment request This credit authorization phase is not particularly time sensitive, as the PoC feature has not yet been invoked. 20 In the event that the credit reservation is unsuccessful (e.g. the user's credit balance is exhausted), the PPS initiates the Immediate Service Termination procedure by returning a failure indication to the PoC Server (in a Diameter ACA message, with: 25 Result-Code = DIAMETER_END_USER_SERV1CE_DENIED). The PoC Server returns a SIP error indication to the serving IMS Core. An error indication is returned to the UE and end-user. As already mentioned, when credit is reserved at early session establishment, 30 the PoC Sever is not aware yet of which PoC feature will be invoked at a later time, or indeed whether the UE performing the early session establishment procedure will be used by tie origination (session-owner) or terminating (participant) end-user. Thus, at early session establishment the PoC Sever 10 may only provide limited input for rating to the Prepaid System. At session connection (i.e. the actual PoC feature invocation/set-up stage), the PoC Sever processes the service request immediately, by relying on the previously reserved credit The PoC Server is now able to provide precise input for rating to the PPS (in a Diameter ACR message, with Accounting-Record-Type = INTERIM). This credit authorization phase is again not particularly time sensitive because an estimated credit amount has been already reserved, reducing the risk to the service provider. The service invocation can be processed immediately, write in parallel a scowl credit out to refine the rating. Figure 4 illustrates the signaling associated with the early session establishment procedure when used for advanced credit reservation with the Instant Personal Talk feature. This scenario provides for an early session establishment procedure at both sides. (NB. the signing flow does not show the originating and terminating IMS Core.) The various signaling steps are as follows: Network-A early session establishment 20 1a. UE-A begins early session establishment (immediately after initial IMS registration or at some later point in time, e.g. when the user activates the Instant Talk service from the UE) by sending a SIP INVITE towards PoC Server A, via IMS Core A (i.e. UE sends SIP INVITE to IMS Core A). The IMS Core A returns a SIP 100 Trying" to UE A. The IMS Core A detects an originating 25 trigger and as a result sends the SIP INVITE to PoC Server A. The SIP INVITE includes: Request-URI user part set to pre-configured string "Ad-hoc Group Request(the string is configured in the UE) Accept-Contact including the feature tag M+g.poc.talkburt=TRUE 30 To = URI user part set to pre-configured string "Ad-hocGroupRequest From = inviting user's Public User Identity Message body with Content Type’ application’ containing an SDP offer 1 11 2a. PoC Server A checks that early session is supported. For the purpose of this scenario ft is assumed that early session is supported. PoC Server A may send a SIP 100 Trying to IMS Core A. 5 Charging in Network-A. first interrogation 3a. The Controlling PoC Server starts a credit-control session towards user-A's home Prepaid System A while continuing processing the received session setup request/SIP INVITE. The Prepaid System A is identified by the ECF address 10 downloaded as part of user A profile from Home Subscriber System (HSS) to the S-CSCF in IMS Core A at IMS user A registration time and transferred in the SIP INVITE from the S-CSCF in IMS Core A to PoC Server A. 4a. The Controlling PoC Server sends a Diameter ACR to Prepaid System A. IS The Diameter ACR includes: Accounting-Record-Type=START_RECORD Subscription-Id (Type=END_USER_SIP_URL, Data=’user-A SIP URT) M-S-C-C(#1) Service – parameter- Info(Type=ExtentionNumber1, 20 Value=POC_ANY_TALK_SESSION) Service-Parameter -lnfo (Type=ExtenstonNurnber2, Value=session-owner) Requested-Service-Unit (Type=SERVICE_CREDIT_EVENT, Value^pre-configured value') Service-Parameter-lnfo (Type=Extension Number A, 25 Value= e.g. "total time session is up" M-S-C-C(#2) Service-Parameter -Info(Type=Extension Number2 Value=session – owner) Service-Pararneler-lnfo (Type=ExtensionNurnber2, 30 Value=session – owner) Requested-Service-Unit(Type-Service_CREDIT_EVENT Value Pre-configured value) Service –Parameter-Info (Type-ExtensionNumberC 12 Value= e.g. "number of distributed talk bursts" M-S-C-C (#n) Service-Parameter-info (Type=ExtensionNumber1, Value=POC_ANY_TALK_SESSION) 5 Service-Parameter-Info (Type=ExtensionNumber2 Value=session-participant) Requested-Service-Unit (Types=SERVICE_CREDIT_EVENT, Value=pre-configured value') Service-Parameter-Info (Type=ExtensionNumberBB, 10 Value= e.g. "number of sent and/or received talk burst" NOTE: in this example three M-S-C-C AVPs are include/shown. in general, several M-S-C-C AVPs may be included, one far each measurement method supported by the PMM SE for the concerned service-type and party-role 15 combination 5a. Prepaid System-A tentatively rates the service (it is unknown at this stage whether any future requested service will be Instant Personal Talk or Ad-hoc Instant Group Talk), based on the contents of the received Service-Parameter- 20 Info, makes a credit-reservation from the end-user's account (that covers the anticipated cost of the service) and returns a Diameter ACA message to the PoC Server. For the purpose of this scenario the user's credit balance is assumed to be sufficient The Diameter ACA includes: Result-Code=DIAMETER_SUCCESS 25 Accounting-Record-Type=START_RECORD Accounting-lnterim-lnterval (Value set by the Prepaid System') Subscription-Id (Type=END_USER_SIP_URL, Data=user-A SIP URI') M-S-C-C (#a) Service-Parameter-lnfo (Type=ExterisicnNurnber1, 30 Value=POC_ANY_TALK_SESSION) Service-Parameter-Info (Type=ExtensionNumber2 Value Session-owner) Granted-Service-Unit (Type=SERVICE_CREDIT_EVENT, 13 Value='Prepaid System sets Granted-Service-Unit value = Requested-Service-Unit value') Service-Parameter-info (Type=ExtensionNumberC, Value= e.g. "number of distributed talk bursts'). Note: it is the 5 charging model in force if the user will later take the role of session-owner. M-S-C-C(#b) Service-Parameter-Info (Type=ExtensionNumber1, Value=POC_ANY_TALK_SESSION) 10 Service-Parameter-Info (Type=ExtensionNumber2, Value= session-participant) Granted-Service-Unit (Type=SERVICE_CRED(T_EVENT, Value Prepaid System sets Granted-Service-Unit value = Requested-Service-Unit value") 15 Service-Parameter-Info (Type=, ExtensionNumberBB Values "sent talk burst"). Note: it is the charging rnodel in force if the user will later take the role of session-participant. The Controlling PoC Server A starts monitoring the usage of the granted-20 service-units. Early session establishment proceeds 6a. PoC Server A sends a SIP 202 Accepted to UE A via IMS Core A. The SIP 25 202 Accepted includes: Contact, containing the transient ad-hoc group identifier generated by the Controlling PoC Server Message body with Content Type "application/sdp" containing an SDP Answer 1 30 7a. UE A sends a SIP ACK to PoC Server A Via IMS Core A 14 In parallel to steps 1a through 7a in Network A, steps 1b though 7b take place in Network B (involving User B, UE B, IMS Core B, PoC Server B, Prepaid System B). Early session -connection After completion of the early session establishment procedure illustrated in Figure 4, the connection procedure is initiated by a subscriber (UE-A in this 10 case). Figures 5 and 6 illustrates signalling associated with an Instant Personal Talk establishment (l.e. connection setup). Again, the skjnaJRng flow does not show the originating and terminating IMS Core. The signalling steps are as follows. 15 Connection set-up with early session 1. The end-user at UE A, subscriber of Network A, presses the PoC button to initiate an Instant Personal Talk session with end-user at UE B, subscriber of Network B. 20 2. UE-A sends a SIP REFER to PoC Server A, via IMS Core A. The SIP REFER includes: Refer-To: invited user's Public User Identity (i.e. SIP URI or E.164 number) 3. The originating Participating PoC Server A recognizes the session type as Instant Personal Talk, based on the information in the SIP REFER (i-e. one Public User Identity). 30 The originating Participating PoC Server A takes the function of Controlling PoC Server. The originating participating PoC Server function is logically co-located with the Controlling PoC Server function. That Is, for Instant Personal Talk, the PoC Server assigned to the inviting user is the Controlling PoC Server. 15 The Controlling PoC Server shall: Authorizes the inviting user to the talk session; Interpret the SIP REFER as an implicit subscription request to a refer event 5 package for each outgoing SIP INVITE/REFER (i.e. the inviting UE shall receive information about invited users' final SIP response in a SIP NOTIFY); and Interpret the SIP REFER as an implicit "floor request" Charging in Network-A. intermediate interrogation 10 4. The controlling PoC Server performs an intermediate interrogation to provide additional rating input to Charging System A, La. toe Controlling PoC Server now has knowledge that the session is of type Instant Personal Talk, IS 5. The Controlling PoC Server sends a Diameter ACR to Prepaid System A. The diameter ACR includes: Accounting Record Type=INTERIM_RECORD Subscription-Id (Type=ENDJJSER_SIP_URL, Data-user-A SIP URT) M-S-C-C 20 Service-parameter-lnfo (Type=ExtensionNumber, Value=POC_INSTANT_PERSONAL_TALK) Service-Parameter-Unit (Type=ExtensionNumber2, Value= session-owner) Requested-Service-Unit (Type=SERVlCE_CREDIT_EVENT, 25 Values=pre-configured value') Used-Service-Unit (Type=ExtentionNumberC Value=amount of used service units') Service-Parameter-Info (Type=ExtensionNumberC, Value e.g. "number of distributed talk bursts") 30 6. Prepaid System-A deducts the used amount from the end- account, rates the service based on e contents of the received Service-Parameter-Info, makes a new credit reservation from the end user account (That covers 16 the cost of the service) and returns a Diameter ACA. For the purpose of this scenario the user's credit balance is sufficient The Diameter ACA includes: Result-Code=DIAMETER_SUCCESS Accounting-Record-Type»INTERIM _RECORD Accounting-lnterim - interval ("value set by the Prepaid System') Subscription-Id (Type=END_USER_SIP_URL, Data='user-A SIP URI') M-S-C-C Service-Parameter-info (Type=ExtensionNumber1, Value=MK)CJNSTANT_PERSONAL_TALK) 10 Service-Parameter-Info (Type=ExtensionNumber2, Value9 session-owner) Granted-Service -Unit (Type=SERVICE_CREDIT_EVENT, Value Prepaid System sets Granted-Service-Unit value = Requested-Service-Unit value') 15 Service-Parameter-lnfo Type=ExtentionNumberC Values e,g "number of distributed talk bunts") 7. The Controlling PoC Server A continues monitoring the usage of the granted-service-units. 20 8. Controlling PoC Server A sends a SIP 202 Accepted to UE A, via IMS Core A. 9. Controlling PoC Server A sends a SIP INVITE (SDP Offer 2) to 25 Participating PoC Server B. it will be appreciated that this message can be sent immediately by the PoC Server A, following receipt of the SIP REFER message from UE A, i.e. this message may be sent before or during the exchange of DIAMETER messages (5 and 6). 30 10. The Participating PoC Server B gets (from GLMS functionally) the Do-not-Disturb flag, the access (accepting) invited user. Of the Server B authorities the request based on the Do-not-Disturb flan and the access (accept/reject) lists of the invited user. 17 For the purpose of this scenario, the Participating PoC Server B determines that the DnD flag is not set, the inviting user is not on the reject list, and the invited user's answer mode is set to "auto answer". 5 Charging in Network-B. intermediate interrogation 11. The participating PoC Server performs an intermediate interrogation to provide new/ additional rating input to Charging System A, i.e. the Participating PoC Server now has knowledge of terminating PoC session. 10 12. The Participating PoC Server sends a Diameter ACR to Prepaid System B. The Diameter ACR includes: Accounting_Records-Types=INTERM_RECORDS Subscription-Id (Type=END_USE_SJP_URL, Date=user-A SIP URT) 15 M-S-C-C Service-Parameter-lnfo( Type=ExtentionNumberC Value=POC_ANY_SESSION) Service-Parameter-lnfo( Type=ExtentionNumberC Value= session-participant) 20 Requested-Service=UNIT(Type==SERVICE_CREDIT_EVENT, Value=pre-configured value') Used-Service-Unit (Type=SERVICE_CREDIT_EVENT, Value-amount of used service units') Service-Parameter-Info (Type=ExtensionNumberBB, 25 Value= "sent talk burst") 13. Prepaid System-B deducts the used amount from the end-user's account, rates the service, based on the contents of the received Service-Parameter- Info, makes a new credit-reservation from the end-user's account (that covers 30 the cost of the service) and returns a Diameter ACA. For the purpose of this scenario the user's credit balance Result-Code=DlAMETER_SUCCESS Accounting_Records-Types=INTERM_RECORDS 18 Accounting-Interim-Interval ('value set by the Prepaid System') Subscription-Id (Type=END_USER_SIP_URL, Data=user-A SIP URI) M-S-C-C Service-Parameter-lnfo (Type=ExtensionNumber, 5 Value=POC_ANY_TALK_SESSION) Service-Parameter-lnfo (Type=ExtensionNurnber2, Value= session-participant) Granted-Service-Unit (Type=(Type=SERVICE_CREDIT_EVENT, Value='Prepaid System sets Granted-Service-Unit value = 10 Requested- Service- Unit-value) Service-Parameter-lnfo (Type=ExtensionNurnberBB Value=sent talk brust”) " 14. The Participating PoC Server B starts monitoring the usage of tie grantod-15 service-units. Connection set-up with early session proceeds 15. UE-B has an established early session and has auto answer mode set; 20 thus, the Participating PoC Server B selects early media mode. 16. Participating PoC Server B sends a SIP 200 OK (SOP Answer 2) to Controlling PoC Server. 25 17. SIP ACK is sort from controlling PoC Server A to Pa B. tt is noted that, as with the SIP INVITE message (9), the sending of the SIP ACK and SIP 200 OK messages is independent of the exchange of DIAMETER messages (5,6,12,13). 30 18. Controlling PoC Server sends RTCP "floor taken" to UEB, via Participating PoC Server B. 20. Controlling PoC Server sends RTCP "floor granted" to UE A. It is noted that, as with the SIP INVITE message (9), the sending of the messages RTCP "floor taken" (18) and RTCP "floor granted" (20) is independent of the exchange 5 of DIAMETER messages (5,6,12,13). 21. A "talk indication" is give to user A (both "SIP 202 Accepted" carrying the SDP Answer, and "RTCP floor granted" indicating that PoC Server is ready to handle media, are needed for user interaction purposes). 10 User A beams talking 22. User A starts to talk. 15 23. TOP talk burst(media) is transmitted from UE A to U^ PoC Server and Participating PoC Server B. 24. User A listen to user B's speech phrase. 20 25. Due to previous "implicit subscription to invited user status" upon receipt of SIP 200 OK, the Controlling PoC Server sends a SIP NOTIFY request to IMS Core A IMS Core A sends the SIP NOTIFY to UE A. The SIP NOTIFY includes: Event = refer Message body with Content Type "messaoe/sipfrag" containing: 25 The status line of the SIP response that the PoC Server received from the invited user, "SIP/2.0 200 OK" for this scenario; and The Public User Identify of the invited user (SP URI or MSISDN). 26. UE A sends a SIP 200 OK response to the SIP NOTIFY to IMS Core A. 30 IMS Core A sent the SIP 200 OK to Controlling PoC Server. User A ends Talking 20 27. User A releases the PoC button. 28. UE A sends "RTCP floor release" to Controlling PoC Server. 5 29. Controlling PoC Server sends "RTCP floor idle" to UEA. 30. Controlling PoC Server sends "RTCP floor Idle" Participating PoC Server B, which forwards it to UE B. lO 31. A "floor idle indication" is given to user B. Other talk bursts may be sent/received by user-A and user-B. Other credit-control intermediately interrogation may occur. 15 User-A disconnects fawn the talk session 32. User-A requests to disconnect from the talk session. 20 33. UE-A sends a "RTCP BYE" to Controlling PoC Server. 34. Controlling PoC Server detects Inactivity timer expiry. According to the session termination policy the Controlling PoC Server requests talk session release. 25 35. Controlling PoC Server sends "RTCP BYE" to Participating PoC Server B, which forwards it to UE-B. 36. A session disconnect indication is given to user B. 30 37. Controlling PoC Server sends a SIP BYE to Participating PoC Server B. 38. Participating PoC Server B responds with SIP 200 OK (for SIP BYE). 21 Charging in Network-A. final interrogation 39. The Controlling PoC Server sends a Diameter ACR to Prepaid System A. 5 The Diameter ACR includes: Accounting-Record-Type=STOP_RECORD Subscription-W (Type=END_USER_SIP_URL, Data=user-A SIP URI") Used-Service-Unit (Types=SERVICE_CREDIT_EVENT, Value=amount of used service units') 10 40. Prepaid System-A returns a Diameter ACA. For the purpose of this scenario the user's credit balance is sufficient The Diameter ACA includes: Result -Code=DIAMETER_SUCCESS Accourrtin9-Record-Typee=STOP_RECORD 15 Charging in network B final Interrogation 41. The Participating PoC Server sends a Diameter ACR to Prepaid System B. The Diameter ACR includes: 20 Accounting Record-Types=STOP_RECORD Subscription-Id (Type=END_USER_SIP_URL, Data='user-A SIP URI*) Used-Service-Unit (Type=SERVlCE_CREDIT_EVENT, Value=amount of used service units') 25 42. Prepaid System-B returns a Diameter ACA. For the purpose of this scenario the user's credit balance is sufficient. The Diameter ACA includes: Result-Code=DIAMETER_SUCCESS Accounting-Record-Type=STOPJRECORD 30 It will be appreciated from the above discussion that the introduction of the prepaid feature (a must for wide market acceptance of certain PoC features) is done in such a way that the credit authorization phase dose not influence the PoC talk session setup time. The PMM Serving Element (e.g. PoC Server) 22 performs credit authorization towards the Prepaid System to reserve credit, at some time after initial IMS user registration as part of the "PoC early session procedure"; that is before the actual set-up time critical PoC service feature (i-e. Instant Personal talk, Ad-hoc Instant Group Talk) is invoked by the end-used. 5 When the end-user invokes the PoC service feature, the IPMM Serving Element can process the service request immediately by relying on the previously reserved credit; at the same time the IPMM Serving Element performing a second credit authorization to provide the Prepaid System with refined rating input (e.g. the actual PoC feature invoked, the role of the session originating 10 party). As result, the credit authorization phase does not influence the PoC talk session set-up time. It will be appreciated by the person of skin in the art that various modifications may be made to the above described embodiments without departing from the 15 scope of the present invention. 23 Appendix Push-to-Talk over Cellular (PoC) is a "walky-4alky" type of service based on IMS technology. The PoC service includes the following features: 5 Instant Personal Talk This is a (1-40-1) voice communication with another user, where the users talk one at a time. A user invites the other user to establish an Instant Personal Talk session. A participating user of the 1-to-1 Instant Personal Talk service 10 may add a new user or users to the session, thus establishing a 1-to-N communication (he. Ad-hoc Instant Group Talk). Chat Group Talk This is a 1-to-N voice communication, where the users speak one at a time. A 15 user joins the group in order to participate h the chat group talk, Le. each participant joins the session individually. There are two types of chat groups: 1. An open chat group is a group that can be joined-in by any user 2. A restricted chat group is a group with member list; only the user who owns the group is able to add and remove group members; only the 20 group members are able to join the chat group talk session A group has to be created and the members have to be defined before a Restricted Chat Group Talk can be established. A group has to be created before an Open Chat Group Talk can be established. A participant in an ongoing open or restricted chat group talk session may add/invite other users to 25 the session; if the group is restricted, a participant may invite only users who are members of the group. Instant Group Talk This is a 1-to-N voice communication, where the users speak one at a time. 30 One of the members of the group invites all other group members to the instant group talk session. A group has to be created and the members have to be defined before an instant Group Talc can be established A member of the group who has left the group or has initially rejected the invitation, may join/ join an ongoing instant group talk session. A participant to an ongoing instant group talk session may add/invite other members of the group to the session. Ad-hoc Instant Group Talk 5 This is a 1-to-N voice communication, where the users speak one at a time. A user invites selected users to an Ad-hoc Instant Group Talk session. A participant to an ongoing ad-hoc instant group talk session may add/invite other users to the session. A user who has left the group or has initially rejected the invitation, may join/re-join an ongoing ad-hoc instant group talk session. 10 Instant Personal Alert A user may alert another user. The alert express the user's wish to communicate and it is way to politely request the other user to cal back using for example the instant personal talk feature. An instant personal alert may 15 carry a text message. In addition, the following capabilities are used in association with the PoC features described above: 20 Group and List Management This allows PoC end-users (and operators) to manage group, lists and other Information, as described below. The information is stored in the network in the Group and List Management Server (GLMS) logical entity, and managed via the UE-GLMS interface. 25 Contact lists These are used for storing contact entries (individuals and group) in the UE and the network. Such lists be used by the UE to address users and groups when initiating PoC communication. Contact lists apply to Instant Personal Talk and 30 Ad-hoc instant Group Talk session types. Access (Accept/Reject) lists These are used to define access rules; that is who is allowed or not allowed to reach a specific user via PoC services (i.e. a called/invited user may use accept and reject lists to accept or reject incoming talk session requests from other users). Access lists apply to all talk session types, and are used by the PoC 5 Server. This is a called/terminating party feature. Group lists Group lists are used to define PoC specific groups, and apply to open/restricted Chat Group Talk and Instant Group Talk. Used by the PoC Server and the UE. 10 Do-not-Disturb (DnD) The called/invited user may use the "Do Not Disturb" feature the block all incoming talk session (expect Instant Personal Alert). DnD takes precedence over the Appose Lists. Used by the PoC Server. This is a called/monitoring IS party feature. Answer Mode The called/invited user may select auto or manual answer modes, and are used by the PoC Server and the UE. It is a called/terminating party feature. The 20 PoC Server serving the invited user may use the answer mode to select the media mode (early or late media) for the session. Presence This feature is used to advise parties of the accessibility of other parties. 26 CLAIMS: 1. A method of reserving credit for a mobile subscriber in respect of an IP Multimedia service, the method comprising: 5 following initial registration of the subscriber to the IP multimedia service but prior to invocation of an IP Multimedia service, using the early session establishment procedure to reserve a credit amount at a charging control node and to notify an IP Multimedia Serving Element of the credit reservation, 10 whereupon, at invocation of said IP Multimedia service, the IP Multimedia Serving Element is able to proceed immediately with the session establishment 2. A method according to claim 1, wherein the early session 15 establishment procedure comprises an exchange of messages between the IP Multimedia Serving Element and the charging contort rode using a DIAMETER based protocol 3. A method according to claim 1 or 2, the early session establishment 20 procedure being triggered automatically following registration of the subscriber to the P multimedia service. 4. A method according to claims 1 or 2, the early session establishment procedure being triggered by the subscriber activating an IP multimedia service. 25 5. A method according to any one of the preceding claims, wherein the IP Multimedia service is a Pusn4o4a!k over Cellular IP Multimedia service. 6. A method according to any one of the preceding claims and 30 comprising, at one of the IP Multimedia Serving Element and the charging control node, estimating an amount of credit appropriate to the IP multimedia service. 27 7. A method according to any one of the preceding claims, wherein said subscriber is a prepaid subscriber and said charging control node is a prepaid system server located in the subscriber's home network. 5 8. A method according to any one of the preceding claims and comprising, at initiation of the IP multimedia session, performing a credit authorization procedure between the IP multimedia Service Element and the charging control node based upon actual session conditions to establish a revised credit amount, and replacing or supplementing the estimated credit 10 amount with the revised credit amount 9. A method of operating an IP multimedia Serving Element arranged to facilitate access to an IP multimedia service by subscribers, the method comprising: IS following initial registration of a subscriber to the P multimedia service, as part of an early session establishment procedure initiating a transaction with a charging control node to reserve a credit amount at the charging control node. 20 10. A method of operating a charging control node arranged to control subscriber access to IP multimedia services, the method comprising: participating in an early session establishment procedure following initial registration of a subscriber to the IP Multimedia service but prior to invocation of the IP Multimedia service, the charging control node estimating an appropriate 25 credit amount to be reserved for a future session. Dated this 29th day of December, 2006 (G. DEEPAK SRINIWAS) OFK&S PARTNERS ATTORNEY FOR THE APPLICANT(S) 28 ABSTRACT CHARGING MECHANISMS FOR IP MULTIMEDIA SERVICES A method of reserving credit for a mobile subscriber in respect of an IP multimedia service. The method comprises, following initial registration of the subscriber to the IP Multimedia service but prior to invocation of an IP Multimedia service, using the early session establishment procedure to reserve a credit amount at a charging control node and to notify an IP Multimedia Serving Element of the credit reservation, whereupon, at invocation of said IP multimedia service, the IP Multimedia Serving Element is able to proceed immediately with the session establishment.

Full Text

FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10, rule 13)
“CHARGING MECHANISMS FOR IP MULTIMEDIA SERVICES"
TELEFONAKTIEBOLAGET LM ERICSSON (PUBL), a company duly organized and existing under the laws of Sweden of SE-164 83 Stockholm, Sweden
The following specification particularly describes the invention and the manner in which it is to be performed.

2
Charging Mechanisms for IP Multimedia Services
Field of the Invention
5
The present invention relates to charging mechanisms for IP Multimedia services and which are applicable in particular, though not necessarily, to Push-to-talk over Cellular services.
10 Background to the Invention
IP Multimedia services provide a dynamic combination of voice, video, messaging, data, etc within the same session. By growing the numbers of basic applications and the media that it is possible to combine, the number of
15 services offered to the end users win grow exponentially, and the inter-personal communication experience will be enriched. This will lead to a new generation of personalized, richer multimedia communication services.
IP Multimedia Subsystem (IMS) is the technology defined by the Third
20 Generation Partnership Project (3GPP) to provide IP Multimedia services over 3G mobile communication networks. IMS provides key features to enrich the end-user person-to-person communication experience through the integration and interaction of services. IMS allows new rich person-to-person (client-to-client) as well as person-to-content (client-to--server) communications over an
25 IP-based network. The IMS makes use of the Session Initiation Protocol (SIP) and Service Delivery Protocol (SDP) to set up and control calls or sessions between user terminals (or user terminals and web servers). Figure 1 illustrates schematically how the IMS fits into the mobile network architecture.
30 Existing cellular telephone network operators have recently experienced tremendous growth in the numbers of subscribers choosing to use so-called "prepaid" subscriptions; that is where subscribers deposit an amount of cash (the credit balance) with their operators, which is consumed by tte subsequent

3
use of services by the subscribers. It is anticipated that the prepaid subscription option will prove equally popular with the users of IPMM services. Indeed, the provision of pre-paid services is likely to be a must for widespread take-up of IPMM services.

When online/readme charging mechanisms are used (as for prepaid users), the general rule would be for the IPMM Serving Element (SE) providing access to the requested service, to request credit authorisation before granting a mobile node access to the requested service. However, this would inevitably
10 increase the session set-up time for prepaid subscribers, as the IPMM SE must conduct a credit authorization transaction with a Charging Control Node, also referred to as a Prepaid System (PPS) or Online Charging System (OCS).
For some IPMM/IMS based services the session set-up time is critical. This
15 applies for example to so-called Push-to-talk over Cellular (PoC) services such as Instant Personal Talk and Ad-hoc Instant Group Talk, where the originating party pushes the PoC button on his/her terminal to invite one or more users to a walkie-talkie type session, and expects to be immediately in contact with the invited party/parties (as opposed to the traditional call, ring, answer based
20 telephony services). The introduction of the prepaid payment mechanism as currently proposed is likely to result in a degradation of the PoC session set-up time to an unacceptable level, or may lead to a sub-optimal user experience due to the additional delay produced by the credit authorisation phase.
25 Summary of the Invention
It is an object of the invention to obviate the effects of prepaid payment mechanisms on actual and perceived subscriber service levels.
30 According to a first aspect of the present invention there is provided a method of reserving credit for a mobile subscriber in respect of an IP Multimedia service,
the method comprising:
following initial registration of the subscriber to the IP Multimedia

4
service but prior to invocation of an IP Multimedia service,
using the early session establishment procedure to reserve a credit
amount at a charging control node and to notify an IP Multimedia Serving
Element of the credit reservation,
5 whereupon, at invocation of said IP Multimedia service, the IP
Multimedia Serving Element is able to proceed immediately with the session connection.
It will be appreciated that the early session establishment procedure will
10 comprise an exchange of appropriate messages between the IP Multimedia Serving Element and the charging control node. The messages may satisfy the requirements of the DIAMETER protocol.
The early session establishment procedure will also typicaly be used for service
negotiation purposes (e.g. exchange of media address and codec types) between the subscriber's terminal (UE) and the IMS Server.
The early session establishment procedure may be triggered automatically following registration of the subscriber to the IP multimedia service, or may be
20 triggered, for example, by the subscriber/end-user activating a particular IP Multimedia service at his/her terminal.
The invention is applicable in particular, though not necessarily, to Push-to-talk over Cellular (PoC) IP Multimedia services.
The method may comprise, at one of the IP Multimedia Serving element and the charging control node, estimating an amount of credit appropriate to the IP Multimedia service. Preferably, this estimate is carried out at the charging control node.
30
In the case of a prepaid subscriber, said changing control rote will be a prepaid system (PPS) server boated h the subscriber's home network.

5

Preferably, the method comprises, at invocation of the IP Multimedia service, performing a credit authorisation procedure between the IP Multimedia Service Element and the charging control node based upon the actual service that has been requested/invoked to establish a revised credit amount The estimated
credit amount Is replaced by the revised credit amount
According to a second aspect of the present invention there is provided a method of operating an IP Multimedia Serving Element arranged to facilitate access to an IP Multimedia service by mobile subscribers, the method
10 comprising:
following initial registration of a subscriber to the IP multimedia service but prior to initiation of the IP multimedia session, initiating an early session establishment procedure with a charging control node to reserve a credit amount at the charging control node.
15
According to a third aspect of the present invention there b provided a method of operating a charging control node arranged to control subscriber access to IP Multimedia services, the method comprising:
participating in an early session establishment procedure following
20 initial registration of a subscriber to the IP Multimedia service but prior to invocation of the IP multimedia service, the charging control node estimating an appropriate credit amount to be reserved for a future session.
Brief Description of the Drawings
25
Figure 1 illustrates schematically a mobile network architecture incorporating an
IP Multimedia Subsystem;
Figure 2 illustrates a simplified logical online charging architecture for an IPMM
services;
30 Figure 3 shows the PoC Release 2 architecture;
Figure 4 shows signalling associated with the early session establishment
procedure for PoC Instant Personal Talk and
Figures 5 and 6 show signaling associated with tie session connection

6
procedure, following early session establishment, when the service is actually invoked.
Detailed Description of Certain Embodiments of the Invention

In an IP Multimedia Subsystem (IMS) session there can be a number of users that are subscribers of several different IMS operators. In any generally applicable charging procedure, each of the IMS operators should be able to charge their own subscribers independently, according to their own charging policy. That is to say that different charging models may be applied in different networks for the same IMS session. Moreover, different charging models may be applied to different sets of subscribers for the same IPMM service/feature, within a given operator's network.
15 According to 3GPPRSTS 32325 and TS 32.200 and ETFDCC(Internet draft "Diameter Credit control application), two scenarios for IMS online charging are
1) "One-Time Event with Direct Debiting* scenario. "Immediate Event Charging^' modelin3GPP. "Credit Authorization with Direct Debiting" model in IETF DCC.
20 2) "Session-based Credit Control" scenario. "Event Charging with Unit Reservation" model in 3GPP. "Credit Authorization with Money Reservation" model in IETF DCC.
In both models the IPMM Serving Elements (IPMM SE), i.e. credit control dent, request credit authorization from the Online Charging System (OCS)Prepaid
25 System (PPS), i.e. the credit control server, prior to allowing any service to be delivered to the end user. The Session-based Credit Control scenario is considered to be more appropriate for most IPMM services, and it is the scenario considered here.
30 Session-based Credit Control is a process in which the PPS rates a request from, a IPMM SE, reserves a suitable amount of money from the user's account, and notifies the IPMM SE of the corresponding amount of credit resources Of course, "credit resource" may not imply actual monetary credit

7
may be granted in the form of units (e.g. data volume or time) to be metered. Upon reception of a successful credit authorisation answer with a certain amount of credit resources, the IPMM SE allows service delivery to the end user and starts monitoring the usage of the granted resources. When the credit
resources granted to the end user have been consumed or the service has been successfully delivered or terminated, the IPMM SE reports back to the PPS the used amount, and the PPS deducts the used amount from the user's account (the PPS may perform rating and make a new credit reservation if the service delivery is continuing). This process includes first interrogation,
10 possible intermediate interrogations, and a final interrogation. Both IPMM SE and PPS are required to maintain credit control session state information.
The upper diagram of Figure 2 illustrates a general online charging architecture for IPMM, whilst the lower diagram lustrates a simplified architecture for PoC.
15 The Online Charging System (OCS) Prepaid System (PPS) provides the charging control function for a real-time charging mechanism. The Prepaid System includes the Account Balance Manager and the User Accounts, the Rating Engine and the Tariff Information. The Rating Engine provides rating values for sessions/services or events not priced at source, i.e. for which
20 serving elements do not have a price. For online charging, the IPMM SEs
which may provide charging input to the PPS, are the Serving-Call Session Control Function (S-CSCF), the Multimedia Resource Function Control (MRFC),
and the Application Server (AS). For Push -to-talk over Cellular (PoC) the SE providing charging input to the PPS is the PoC Server (which embraces MRF
25 and AS functionality). The interlace between the IPMM SEs and the PPS is based on the Diameter Base Protocol (DBP) and the Diameter Credit Control Application (DCC) as is being defined by 3GPP in Release 5 and 6.
Figure 3 shows the PoC Release 2 architecture, where the PoC functional 30 entities are drawn with solid lines. The following interfaces are shown in Figure 3:
It Floor control and media
In: Floor control and media

Is: PoC client to proxies session signalling
If: Proxy to PoC server session signalling
In: Proxy to proxy session signalling
Im: Group management server to PoC client
5 Ik: Group management server to PoC server to: OTAP server to PoC cBent
The PoC architecture has two PoC Server functions, Controlling PoC Server function/logical entity and Participating PoC Server function/logical entity. In
10 each PoC talk session there is only one Controiing PoC Server, whereas there can be one or more Participating PoC Server. The Controlling PoC Server handles the centralized tasks that should not be handled by more than one PoC Server in the PoC talk session. A PoC Server behaves as either a Controlling PoC Server or a Participating PoC Server, as selected on a per PoC talk
15 session basis.
A PoC Server realisation (Le. physical entity/node) may behave as both a Controlling PoC Server and a Participating PoC Server at the same time and for the same PoC talk session. In the case of Instant Personal Talk and Ad-hoc
20 Instant Group TaHc, the PoC Server of the inviting user is the Controlling PoC Server. In case of Chat Group Talc and Instant Group Talk, the Controlling PoC Server is the PoC Server owning/hosting the group identity (the Global Group Identity). Further details of these PoC services are given in the Appendix below.
25
As has been outlined above, the conventional approach to credit reservation for PoC sessions is likely to result in significant session set-up delays. An alternative method of reserving credit for PoC delay sensitive services/features (Le. Instant Personal Talk and Ad-hoc Instant Group Talk) is proposed here
30 which maintains all prepaid characteristics (i.e. operator credit control, end-user real-time spending control). This method makes use of the so-called "early session” establishment procedure to reverse credit for PoC features with
session set-up time before fie end-user initiates a talk session, i.e before the

9
actual PoC feature is invoked. The early session establishment procedure is used for service negotiation purposes (e.g. communication of IP address/port number for RTP/RTCP, and codec types) between the UE and his/her home PoC Server. The early session may be established immediately following IMS
registration or at any later point in time. The early session establishment procedure is defined in the PoC Release 2.0 architecture.
At early session establishment, the PoC Sever performs credit-reservation towards the PPS (by sending a Diameter Accounting Request (ACR), with
10 Accounting-Record-Type = START), before continuing with the processing of the early session establishment request The PPS tentatively rates the service (at this stage it is unknown which PoC feature be invoked by the user at a later time) and, if the user's credit balance is sufficient, the PPS reserves a suitable amount of money from the user's account and returns the
15 corresponding amount of credit units to the PoC Sever fm a Diameter ACA message, with Accounting-Record-Type = START). Upon successful credit reservation, the PoC Server continues processing the early session establishment request This credit authorization phase is not particularly time sensitive, as the PoC feature has not yet been invoked.
20
In the event that the credit reservation is unsuccessful (e.g. the user's credit balance is exhausted), the PPS initiates the Immediate Service Termination procedure by returning a failure indication to the PoC Server (in a Diameter ACA message, with:
25 Result-Code = DIAMETER_END_USER_SERV1CE_DENIED).
The PoC Server returns a SIP error indication to the serving IMS Core. An error indication is returned to the UE and end-user.
As already mentioned, when credit is reserved at early session establishment, 30 the PoC Sever is not aware yet of which PoC feature will be invoked at a later time, or indeed whether the UE performing the early session establishment procedure will be used by tie origination (session-owner) or terminating (participant) end-user. Thus, at early session establishment the PoC Sever

10
may only provide limited input for rating to the Prepaid System. At session connection (i.e. the actual PoC feature invocation/set-up stage), the PoC Sever processes the service request immediately, by relying on the previously reserved credit The PoC Server is now able to provide precise input for rating
to the PPS (in a Diameter ACR message, with Accounting-Record-Type = INTERIM). This credit authorization phase is again not particularly time sensitive because an estimated credit amount has been already reserved, reducing the risk to the service provider. The service invocation can be processed immediately, write in parallel a scowl credit
out to refine the rating.
Figure 4 illustrates the signaling associated with the early session establishment procedure when used for advanced credit reservation with the Instant Personal Talk feature. This scenario provides for an early session establishment
procedure at both sides. (NB. the signing flow does not show the originating and terminating IMS Core.) The various signaling steps are as follows:
Network-A early session establishment
20 1a. UE-A begins early session establishment (immediately after initial IMS registration or at some later point in time, e.g. when the user activates the Instant Talk service from the UE) by sending a SIP INVITE towards PoC Server A, via IMS Core A (i.e. UE sends SIP INVITE to IMS Core A). The IMS Core A
returns a SIP 100 Trying" to UE A. The IMS Core A detects an originating 25 trigger and as a result sends the SIP INVITE to PoC Server A. The SIP INVITE
includes:
Request-URI user part set to pre-configured string "Ad-hoc Group Request(the string is configured in the UE)
Accept-Contact including the feature tag M+g.poc.talkburt=TRUE
30 To = URI user part set to pre-configured string "Ad-hocGroupRequest From = inviting user's Public User Identity
Message body with Content Type’ application’ containing an SDP offer 1

11
2a. PoC Server A checks that early session is supported. For the purpose of this scenario ft is assumed that early session is supported. PoC Server A may send a SIP 100 Trying to IMS Core A.
5 Charging in Network-A. first interrogation
3a. The Controlling PoC Server starts a credit-control session towards user-A's home Prepaid System A while continuing processing the received session setup request/SIP INVITE. The Prepaid System A is identified by the ECF address
10 downloaded as part of user A profile from Home Subscriber System (HSS) to
the S-CSCF in IMS Core A at IMS user A registration time and transferred in the SIP INVITE from the S-CSCF in IMS Core A to PoC Server A.
4a. The Controlling PoC Server sends a Diameter ACR to Prepaid System A. IS The Diameter ACR includes:
Accounting-Record-Type=START_RECORD
Subscription-Id (Type=END_USER_SIP_URL, Data=’user-A SIP URT)
M-S-C-C(#1)
Service – parameter- Info(Type=ExtentionNumber1,
20 Value=POC_ANY_TALK_SESSION)
Service-Parameter -lnfo (Type=ExtenstonNurnber2, Value=session-owner) Requested-Service-Unit (Type=SERVICE_CREDIT_EVENT,
Value^pre-configured value')
Service-Parameter-lnfo (Type=Extension Number A,
25 Value= e.g. "total time session is up"
M-S-C-C(#2)
Service-Parameter -Info(Type=Extension Number2
Value=session – owner)
Service-Pararneler-lnfo (Type=ExtensionNurnber2,
30 Value=session – owner)
Requested-Service-Unit(Type-Service_CREDIT_EVENT
Value Pre-configured value)
Service –Parameter-Info (Type-ExtensionNumberC
12
Value= e.g. "number of distributed talk bursts"
M-S-C-C (#n)
Service-Parameter-info (Type=ExtensionNumber1,
Value=POC_ANY_TALK_SESSION)
5 Service-Parameter-Info (Type=ExtensionNumber2
Value=session-participant)
Requested-Service-Unit (Types=SERVICE_CREDIT_EVENT,
Value=pre-configured value')
Service-Parameter-Info (Type=ExtensionNumberBB,
10 Value= e.g. "number of sent and/or received talk burst"
NOTE: in this example three M-S-C-C AVPs are include/shown. in general, several M-S-C-C AVPs may be included, one far each measurement method supported by the PMM SE for the concerned service-type and party-role
15 combination
5a. Prepaid System-A tentatively rates the service (it is unknown at this stage whether any future requested service will be Instant Personal Talk or Ad-hoc Instant Group Talk), based on the contents of the received Service-Parameter-
20 Info, makes a credit-reservation from the end-user's account (that covers the anticipated cost of the service) and returns a Diameter ACA message to the PoC Server. For the purpose of this scenario the user's credit balance is assumed to be sufficient The Diameter ACA includes:
Result-Code=DIAMETER_SUCCESS
25 Accounting-Record-Type=START_RECORD
Accounting-lnterim-lnterval (Value set by the Prepaid System') Subscription-Id (Type=END_USER_SIP_URL, Data=user-A SIP URI')
M-S-C-C (#a)
Service-Parameter-lnfo (Type=ExterisicnNurnber1,
30 Value=POC_ANY_TALK_SESSION)
Service-Parameter-Info (Type=ExtensionNumber2
Value Session-owner)
Granted-Service-Unit (Type=SERVICE_CREDIT_EVENT,

13
Value='Prepaid System sets Granted-Service-Unit value = Requested-Service-Unit value')
Service-Parameter-info (Type=ExtensionNumberC,
Value= e.g. "number of distributed talk bursts'*). Note: it is the
5 charging model in force if the user will later take the role of
session-owner. M-S-C-C(#b)
Service-Parameter-Info (Type=ExtensionNumber1,
Value=POC_ANY_TALK_SESSION)
10 Service-Parameter-Info (Type=ExtensionNumber2,
Value= session-participant) Granted-Service-Unit (Type=SERVICE_CRED(T_EVENT,
Value Prepaid System sets Granted-Service-Unit value =
Requested-Service-Unit value")
15 Service-Parameter-Info (Type=, ExtensionNumberBB
Values "sent talk burst"). Note: it is the charging rnodel in force if the user will later take the role of session-participant.
The Controlling PoC Server A starts monitoring the usage of the granted-20 service-units.
Early session establishment proceeds
6a. PoC Server A sends a SIP 202 Accepted to UE A via IMS Core A. The SIP
25 202 Accepted includes:
Contact, containing the transient ad-hoc group identifier generated by the
Controlling PoC Server
Message body with Content Type "application/sdp" containing an SDP Answer 1
30
7a. UE A sends a SIP ACK to PoC Server A Via IMS Core A

14
In parallel to steps 1a through 7a in Network A, steps 1b though 7b take place in Network B (involving User B, UE B, IMS Core B, PoC Server B, Prepaid System B).

Early session -connection
After completion of the early session establishment procedure illustrated in Figure 4, the connection procedure is initiated by a subscriber (UE-A in this
10 case). Figures 5 and 6 illustrates signalling associated with an Instant Personal Talk establishment (l.e. connection setup). Again, the skjnaJRng flow does not show the originating and terminating IMS Core. The signalling steps are as follows.
15 Connection set-up with early session
1. The end-user at UE A, subscriber of Network A, presses the PoC button to
initiate an Instant Personal Talk session with end-user at UE B, subscriber of
Network B.
20
2. UE-A sends a SIP REFER to PoC Server A, via IMS Core A. The SIP
REFER includes:
Refer-To: invited user's Public User Identity (i.e. SIP URI or E.164 number)
3. The originating Participating PoC Server A recognizes the session type as Instant Personal Talk, based on the information in the SIP REFER (i-e. one Public User Identity).
30 The originating Participating PoC Server A takes the function of Controlling PoC Server. The originating participating PoC Server function is logically co-located with the Controlling PoC Server function. That Is, for Instant Personal Talk, the PoC Server assigned to the inviting user is the Controlling PoC Server.

15

The Controlling PoC Server shall: Authorizes the inviting user to the talk session;
Interpret the SIP REFER as an implicit subscription request to a refer event
5 package for each outgoing SIP INVITE/REFER (i.e. the inviting UE shall receive information about invited users' final SIP response in a SIP NOTIFY); and Interpret the SIP REFER as an implicit "floor request"
Charging in Network-A. intermediate interrogation 10
4. The controlling PoC Server performs an intermediate interrogation to provide additional rating input to Charging System A, La. toe Controlling PoC Server now has knowledge that the session is of type Instant Personal Talk,
IS 5. The Controlling PoC Server sends a Diameter ACR to Prepaid System A.
The diameter ACR includes:
Accounting Record Type=INTERIM_RECORD
Subscription-Id (Type=ENDJJSER_SIP_URL, Data-user-A SIP URT)
M-S-C-C
20 Service-parameter-lnfo (Type=ExtensionNumber,
Value=POC_INSTANT_PERSONAL_TALK) Service-Parameter-Unit (Type=ExtensionNumber2,
Value= session-owner)
Requested-Service-Unit (Type=SERVlCE_CREDIT_EVENT,
25 Values=pre-configured value')
Used-Service-Unit (Type=ExtentionNumberC
Value=amount of used service units') Service-Parameter-Info (Type=ExtensionNumberC,
Value e.g. "number of distributed talk bursts")
30
6. Prepaid System-A deducts the used amount from the end- account,
rates the service based on *e contents of the received Service-Parameter-Info, makes a new credit reservation from the end user account (That covers

16
the cost of the service) and returns a Diameter ACA. For the purpose of this scenario the user's credit balance is sufficient The Diameter ACA includes:
Result-Code=DIAMETER_SUCCESS
Accounting-Record-Type»INTERIM _RECORD
Accounting-lnterim - interval ("value set by the Prepaid System')
Subscription-Id (Type=END_USER_SIP_URL, Data='user-A SIP URI')
M-S-C-C
Service-Parameter-info (Type=ExtensionNumber1,
Value=MK)CJNSTANT_PERSONAL_TALK)
10 Service-Parameter-Info (Type=ExtensionNumber2,
Value9 session-owner)
Granted-Service -Unit (Type=SERVICE_CREDIT_EVENT,
Value Prepaid System sets Granted-Service-Unit value =
Requested-Service-Unit value')
15 Service-Parameter-lnfo Type=ExtentionNumberC
Values e,g "number of distributed talk bunts")
7. The Controlling PoC Server A continues monitoring the usage of the
granted-service-units.
20
8. Controlling PoC Server A sends a SIP 202 Accepted to UE A, via IMS Core
A.
9. Controlling PoC Server A sends a SIP INVITE (SDP Offer 2) to
25 Participating PoC Server B. it will be appreciated that this message can be
sent immediately by the PoC Server A, following receipt of the SIP REFER message from UE A, i.e. this message may be sent before or during the exchange of DIAMETER messages (5 and 6).
30 10. The Participating PoC Server B gets (from GLMS functionally) the Do-not-Disturb flag, the access (accepting) invited user. Of the Server B authorities the request based on the Do-not-Disturb flan and the access (accept/reject) lists of the invited user.

17
For the purpose of this scenario, the Participating PoC Server B determines that the DnD flag is not set, the inviting user is not on the reject list, and the invited user's answer mode is set to "auto answer".
5 Charging in Network-B. intermediate interrogation
11. The participating PoC Server performs an intermediate interrogation to
provide new/ additional rating input to Charging System A, i.e. the Participating
PoC Server now has knowledge of terminating PoC session.
10
12. The Participating PoC Server sends a Diameter ACR to Prepaid System B.
The Diameter ACR includes:
Accounting_Records-Types=INTERM_RECORDS
Subscription-Id (Type=END_USE_SJP_URL, Date=user-A SIP URT)
15 M-S-C-C
Service-Parameter-lnfo( Type=ExtentionNumberC
Value=POC_ANY_SESSION)
Service-Parameter-lnfo( Type=ExtentionNumberC
Value= session-participant)
20 Requested-Service=UNIT(Type==SERVICE_CREDIT_EVENT,
Value=pre-configured value') Used-Service-Unit (Type=SERVICE_CREDIT_EVENT,
Value-amount of used service units')
Service-Parameter-Info (Type=ExtensionNumberBB,
25 Value= "sent talk burst")
13. Prepaid System-B deducts the used amount from the end-user's account,
rates the service, based on the contents of the received Service-Parameter-
Info, makes a new credit-reservation from the end-user's account (that covers
30 the cost of the service) and returns a Diameter ACA. For the purpose of this scenario the user's credit balance
Result-Code=DlAMETER_SUCCESS
Accounting_Records-Types=INTERM_RECORDS

18
Accounting-Interim-Interval ('value set by the Prepaid System') Subscription-Id (Type=END_USER_SIP_URL, Data=user-A SIP URI*)
M-S-C-C
Service-Parameter-lnfo (Type=ExtensionNumber,
5 Value=POC_ANY_TALK_SESSION)
Service-Parameter-lnfo (Type=ExtensionNurnber2,
Value= session-participant)
Granted-Service-Unit (Type=(Type=SERVICE_CREDIT_EVENT,

Value='Prepaid System sets Granted-Service-Unit value =
10 Requested- Service- Unit-value)
Service-Parameter-lnfo (Type=ExtensionNurnberBB
Value=sent talk brust”)

" 14. The Participating PoC Server B starts monitoring the usage of tie grantod-15 service-units.
Connection set-up with early session proceeds
15. UE-B has an established early session and has auto answer mode set;
20 thus, the Participating PoC Server B selects early media mode.
16. Participating PoC Server B sends a SIP 200 OK (SOP Answer 2) to
Controlling PoC Server.
25 17. SIP ACK is sort from controlling PoC Server A to Pa
B. tt is noted that, as with the SIP INVITE message (9), the sending of the SIP ACK and SIP 200 OK messages is independent of the exchange of DIAMETER messages (5,6,12,13).
30 18. Controlling PoC Server sends RTCP "floor taken" to UEB, via Participating
PoC Server B.

20. Controlling PoC Server sends RTCP "floor granted" to UE A. It is noted
that, as with the SIP INVITE message (9), the sending of the messages RTCP
"floor taken" (18) and RTCP "floor granted" (20) is independent of the exchange
5 of DIAMETER messages (5,6,12,13).
21. A "talk indication" is give to user A (both "SIP 202 Accepted" carrying the
SDP Answer, and "RTCP floor granted" indicating that PoC Server is ready to
handle media, are needed for user interaction purposes).
10
User A beams talking
22. User A starts to talk.
15 23. TOP talk burst(media) is transmitted from UE A to U^ PoC Server and Participating PoC Server B.
24. User A listen to user B's speech phrase.
20 25. Due to previous "implicit subscription to invited user status" upon receipt of SIP 200 OK, the Controlling PoC Server sends a SIP NOTIFY request to IMS Core A IMS Core A sends the SIP NOTIFY to UE A. The SIP NOTIFY includes: Event = refer
Message body with Content Type "messaoe/sipfrag" containing:
25 The status line of the SIP response that the PoC Server received from the
invited user, "SIP/2.0 200 OK" for this scenario; and The Public User Identify of the invited user (SP URI or MSISDN).
26. UE A sends a SIP 200 OK response to the SIP NOTIFY to IMS Core A. 30 IMS Core A sent the SIP 200 OK to Controlling PoC Server.
User A ends Talking
20
27. User A releases the PoC button.
28. UE A sends "RTCP floor release" to Controlling PoC Server.
5 29. Controlling PoC Server sends "RTCP floor idle" to UEA.
30. Controlling PoC Server sends "RTCP floor Idle" Participating PoC Server B, which forwards it to UE B.
lO 31. A "floor idle indication" is given to user B.
Other talk bursts may be sent/received by user-A and user-B.
Other credit-control intermediately interrogation may occur. 15
User-A disconnects fawn the talk session
32. User-A requests to disconnect from the talk session. 20 33. UE-A sends a "RTCP BYE" to Controlling PoC Server.
34. Controlling PoC Server detects Inactivity timer expiry. According to the
session termination policy the Controlling PoC Server requests talk session
release.
25
35. Controlling PoC Server sends "RTCP BYE" to Participating PoC Server B, which forwards it to UE-B.
36. A session disconnect indication is given to user B.
30
37. Controlling PoC Server sends a SIP BYE to Participating PoC Server B.
38. Participating PoC Server B responds with SIP 200 OK (for SIP BYE).

21
Charging in Network-A. final interrogation
39. The Controlling PoC Server sends a Diameter ACR to Prepaid System A.
5 The Diameter ACR includes:
Accounting-Record-Type=STOP_RECORD Subscription-W (Type=END_USER_SIP_URL, Data=user-A SIP URI")
Used-Service-Unit (Types=SERVICE_CREDIT_EVENT, Value=*amount of used service units')
10
40. Prepaid System-A returns a Diameter ACA. For the purpose of this
scenario the user's credit balance is sufficient The Diameter ACA includes:
Result -Code=DIAMETER_SUCCESS
Accourrtin9-Record-Typee=STOP_RECORD
15
Charging in network B final Interrogation
41. The Participating PoC Server sends a Diameter ACR to Prepaid System B.
The Diameter ACR includes:
20 Accounting Record-Types=STOP_RECORD
Subscription-Id (Type=END_USER_SIP_URL, Data='user-A SIP URI*) Used-Service-Unit (Type=SERVlCE_CREDIT_EVENT, Value=amount of used service units')
25 42. Prepaid System-B returns a Diameter ACA. For the purpose of this scenario the user's credit balance is sufficient. The Diameter ACA includes: Result-Code=DIAMETER_SUCCESS Accounting-Record-Type=STOPJRECORD
30 It will be appreciated from the above discussion that the introduction of the prepaid feature (a must for wide market acceptance of certain PoC features) is done in such a way that the credit authorization phase dose not influence the PoC talk session setup time. The PMM Serving Element (e.g. PoC Server)

22
performs credit authorization towards the Prepaid System to reserve credit, at some time after initial IMS user registration as part of the "PoC early session procedure"; that is before the actual set-up time critical PoC service feature (i-e. Instant Personal talk, Ad-hoc Instant Group Talk) is invoked by the end-used.
5 When the end-user invokes the PoC service feature, the IPMM Serving Element can process the service request immediately by relying on the previously reserved credit; at the same time the IPMM Serving Element performing a second credit authorization to provide the Prepaid System with refined rating input (e.g. the actual PoC feature invoked, the role of the session originating
10 party). As result, the credit authorization phase does not influence the PoC talk session set-up time.
It will be appreciated by the person of skin in the art that various modifications may be made to the above described embodiments without departing from the
15 scope of the present invention.

23
Appendix
Push-to-Talk over Cellular (PoC) is a "walky-4alky" type of service based on IMS technology. The PoC service includes the following features:
5
Instant Personal Talk
This is a (1-40-1) voice communication with another user, where the users talk one at a time. A user invites the other user to establish an Instant Personal Talk session. A participating user of the 1-to-1 Instant Personal Talk service
10 may add a new user or users to the session, thus establishing a 1-to-N communication (he. Ad-hoc Instant Group Talk).
Chat Group Talk
This is a 1-to-N voice communication, where the users speak one at a time. A
15 user joins the group in order to participate h the chat group talk, Le. each participant joins the session individually. There are two types of chat groups:
1. An open chat group is a group that can be joined-in by any user
2. A restricted chat group is a group with member list; only the user who owns the group is able to add and remove group members; only the
20 group members are able to join the chat group talk session
A group has to be created and the members have to be defined before a Restricted Chat Group Talk can be established. A group has to be created
before an Open Chat Group Talk can be established. A participant in an ongoing open or restricted chat group talk session may add/invite other users to
25 the session; if the group is restricted, a participant may invite only users who are members of the group.
Instant Group Talk
This is a 1-to-N voice communication, where the users speak one at a time.
30 One of the members of the group invites all other group members to the instant group talk session. A group has to be created and the members have to be defined before an instant Group Talc can be established A member of the group who has left the group or has initially rejected the invitation, may join/

join an ongoing instant group talk session. A participant to an ongoing instant group talk session may add/invite other members of the group to the session.
Ad-hoc Instant Group Talk
5 This is a 1-to-N voice communication, where the users speak one at a time. A user invites selected users to an Ad-hoc Instant Group Talk session. A participant to an ongoing ad-hoc instant group talk session may add/invite other users to the session. A user who has left the group or has initially rejected the invitation, may join/re-join an ongoing ad-hoc instant group talk session.
10
Instant Personal Alert
A user may alert another user. The alert express the user's wish to communicate and it is way to politely request the other user to cal back using for example the instant personal talk feature. An instant personal alert may
15 carry a text message.
In addition, the following capabilities are used in association with the PoC features described above:
20 Group and List Management
This allows PoC end-users (and operators) to manage group, lists and other Information, as described below. The information is stored in the network in the Group and List Management Server (GLMS) logical entity, and managed via the UE-GLMS interface.
25
Contact lists
These are used for storing contact entries (individuals and group) in the UE and the network. Such lists be used by the UE to address users and groups when initiating PoC communication. Contact lists apply to Instant Personal Talk and
30 Ad-hoc instant Group Talk session types.
Access (Accept/Reject) lists

These are used to define access rules; that is who is allowed or not allowed to reach a specific user via PoC services (i.e. a called/invited user may use accept and reject lists to accept or reject incoming talk session requests from other
users). Access lists apply to all talk session types, and are used by the PoC 5 Server. This is a called/terminating party feature.
Group lists
Group lists are used to define PoC specific groups, and apply to open/restricted
Chat Group Talk and Instant Group Talk. Used by the PoC Server and the UE.
10
Do-not-Disturb (DnD)
The called/invited user may use the "Do Not Disturb" feature the block all incoming talk session (expect Instant Personal Alert). DnD takes precedence over the Appose Lists. Used by the PoC Server. This is a called/monitoring
IS party feature.
Answer Mode
The called/invited user may select auto or manual answer modes, and are used by the PoC Server and the UE. It is a called/terminating party feature. The
20 PoC Server serving the invited user may use the answer mode to select the media mode (early or late media) for the session.
Presence
This feature is used to advise parties of the accessibility of other parties.

26
CLAIMS:
1. A method of reserving credit for a mobile subscriber in respect of an
IP Multimedia service, the method comprising:
5 following initial registration of the subscriber to the IP multimedia
service but prior to invocation of an IP Multimedia service, using the early
session establishment procedure to reserve a credit amount at a charging
control node and to notify an IP Multimedia Serving Element of the credit
reservation,
10 whereupon, at invocation of said IP Multimedia service, the IP
Multimedia Serving Element is able to proceed immediately with the session establishment
2. A method according to claim 1, wherein the early session
15 establishment procedure comprises an exchange of messages between the IP
Multimedia Serving Element and the charging contort rode using a DIAMETER based protocol
3. A method according to claim 1 or 2, the early session establishment
20 procedure being triggered automatically following registration of the subscriber
to the P multimedia service.
4. A method according to claims 1 or 2, the early session establishment
procedure being triggered by the subscriber activating an IP multimedia service.
25
5. A method according to any one of the preceding claims, wherein the
IP Multimedia service is a Pusn4o4a!k over Cellular IP Multimedia service.
6. A method according to any one of the preceding claims and
30 comprising, at one of the IP Multimedia Serving Element and the charging
control node, estimating an amount of credit appropriate to the IP multimedia service.

27
7. A method according to any one of the preceding claims, wherein
said subscriber is a prepaid subscriber and said charging control node is a prepaid system server located in the subscriber's home network.
5 8. A method according to any one of the preceding claims and
comprising, at initiation of the IP multimedia session, performing a credit authorization procedure between the IP multimedia Service Element and the charging control node based upon actual session conditions to establish a revised credit amount, and replacing or supplementing the estimated credit
10 amount with the revised credit amount
9. A method of operating an IP multimedia Serving Element arranged
to facilitate access to an IP multimedia service by subscribers, the
method comprising:
IS following initial registration of a subscriber to the P multimedia
service, as part of an early session establishment procedure initiating a transaction with a charging control node to reserve a credit amount at the charging control node.
20 10. A method of operating a charging control node arranged to control
subscriber access to IP multimedia services, the method comprising:
participating in an early session establishment procedure following initial registration of a subscriber to the IP Multimedia service but prior to invocation of the IP Multimedia service, the charging control node estimating an appropriate
25 credit amount to be reserved for a future session.
Dated this 29th day of December, 2006
(G. DEEPAK SRINIWAS) OFK&S PARTNERS ATTORNEY FOR THE APPLICANT(S)

28
ABSTRACT
CHARGING MECHANISMS FOR IP MULTIMEDIA SERVICES
A method of reserving credit for a mobile subscriber in respect of an IP multimedia service. The method comprises, following initial registration of the subscriber to the IP Multimedia service but prior to invocation of an IP Multimedia service, using the early session establishment procedure to reserve a credit amount at a charging control node and to notify an IP Multimedia Serving Element of the credit reservation, whereupon, at invocation of said IP multimedia service, the IP Multimedia Serving Element is able to proceed immediately with the session establishment.

CHARGING MECHANISMS FOR IP MULTIMEDIA SERVICES

Documents:

Inventors:

PCT Conventions: