Abstract:
A method of transporting image or video information between end user terminals via a packet switched network whilst a circuit switched connection is established between the end users includes establishing a circuit switched connection between a plurality of end user terminals for carrying voice traffic. The method also includes using the. Message Session Relay Protocol (MSRP) to encapsulate image or video information transmitted between end user terminals via a packet switched network, where MSRP related traffic is routed between said end user terminals via one or more MSRP enabled nodes. Additionally, the method includes installing service policies into the or at least one MSRP node from a session initiation protocol (SIP) application server (AS) located in the control-plane of an IMS network and checking multimedia service requests against the installed policies to control end user terminal access to certain packet based services.

Description:
FIELD OF THE INVENTION 
     The present invention relates to combinational multimedia services and in particular, though not necessarily, to a method for encapsulating contents exchanged between users, enforcing network policy on such contents, and generating charging reports. 
     BACKGROUND TO THE INVENTION 
     An IP Multimedia service involves the dynamic combination of voice, video, messaging, etc. within the same session. By growing the number of basic applications and the media that it is possible to combine, the number of services offered to the end user will grow exponentially and the inter-personal communication experience will be enriched. This will lead to a new generation of personalized, richer multimedia communication. 
     A combinational IP Multimedia service is a Multimedia service that includes and combines both a Circuit Switched media (such as voice) and a Packet Switched media over the IP Multimedia Subsystem (IMS) (such as pictures, video, presence, instant messages, etc.). Combinational IP Multimedia enables a user during a Circuit Switched (CS) voice conversation with another user to take a picture, an audio/video clip, etc. and transmit this content to the other party in the conversation. Either party in the conversation may initiate transmission of content to the other party. IMS is the technology as defined by 3 GPP to provide IP Multimedia services.  FIG. 1  illustrates a family of combinational services referred to below as weShare, whilst  FIG. 2  illustrates the IMS architecture in 3 GPP. 
     A combinational IP multimedia service requires a protocol to carry the images (or audio/video clip, video, etc) during the CS call. Images/Clips must be transferred using a transport protocol such as TCP, which takes care of retransmissions and ensures that the packets, which the images/clips are broken into, are delivered in order. There also needs to be a user-plane protocol at a higher level (above TCP) that delimits the transfer of an image/clip Message Session Relay Protocol (MSRP) is a candidate for transferring content such as images or video-lips. MSRP is being specified by IETF and is currently described in the document “draft-ieff-simple-message-sessions-08.txt”. MSRP provides a mechanism to transport session-mode contents (e.g. instant messages, pictures, etc.) between endpoints. However, aspects such as weShare service-specific policy enforcement and charging reporting are not covered by the MSRP and by the 3 GPP IMS standards. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provided a method of transporting information between end user terminals via a packet switched-based IP Multimedia Subsystem network whilst a circuit switched connection is established between the end users, the method comprising:
         using the Message Session Relay Protocol, MSRP, to encapsulate information blocks transmitted between users.       

     Preferably, MSRP related traffic is routed between said end user terminals via one or more MSRP-enabled nodes. The or each MSRP-enabled node is preferably coupled to a SIP Application Server (SIP AS) which controls subscriber access to IP multimedia subsystem based services. The MSRP-enabled node is preferably a Media Resource Function (MRF) element. 
     At IMS session set-up, the incoming SIP signaling (i.e. SIP INVITE) is first processed by the SIP AS, which executes service logic (e.g. subscription authorization). As part of service logic execution, the SIP AS prepares and stores a vXML (voice over extended Markup Language) script to be later retrieved by the MRF. The vXML script contains instruction on the policy to be enforced, such as allowed content type (e.g. image/gif, image/jpeg, video-clip), content size (kbytes), and send/receive direction. 
     Once the SIP AS accepts the SIP INVITE (e.g. user is authorized to the invoked weShare service), the SIP AS acts as a proxy server and transmits the SIP INVITE to the MRF. Before proxying the SIP INVITE, the service logic includes into it the HTTP URI to be used to retrieve the vXML script (e.g. the HTTP URI, which embeds the VXML script identity, may be carried in the SIP Request-URI or in a SIP Route header). The MRF receives the SIP INVITE and uses the HTTP protocol to retrieve the vXML script from the SIP AS using the HTTP URI. 
     In particular, the MRF uses the received policy information to:
         possibly downgrade the request from a user terminal during the SIP session establishment (e.g. a request to send a 50 Kbytes jpeg image is downgraded to a maximum allowed size of 40 Kbytes); and   check that the actual content transmitted is in accordance with the specified policy (e.g. a terminal may try sending an image larger than allowed/negotiated and such an action must be rejected).       

     From an HTTP perspective, the SIP AS acts as a vXML server towards the MRF. NOTE: as a complement to SIP, HTTP is just an example of a protocol which might be used over the interface between SIP AS and MRF for retrieval of instructions. 
     From a SIP perspective, the MRF acts as a SIP B2BUA (back to back user agent), and creates a new SIP leg/dialog towards the or each invited UE. 
     From the MSRP perspective, the MRF acts as a back to back end-point. 
     Session Initiation Protocol (SIP) [SIP RFC3261] and Session Description Protocol (SDP) Offer/Answer model are used to establish and negotiate the MSRP session. From the SIP perspective, an MSRP-based content session (e.g. an weShare Image/Clip content session) is considered as any other media session, and therefore is described by SDP. 
     Preferably, for the content transferred via the MRF using MSRP protocol, the MRF reports charging inputs to the charging system. 
     Other aspects of the invention are defined in the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates schematically the services facilitated by the weShare combinational multimedia service; 
         FIG. 2  illustrates schematically the integration of the IP Multimedia Service into a 3 GPP network; 
         FIG. 3  illustrates schematically the weShare service architecture; and 
         FIGS. 4   a  to  4   c  illustrate signaling exchanged between user terminals in connection with a weShare service. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  illustrates the weShare service architecture including a functional split between the Session Initiation Protocol (SIP) Application Server (AS) providing service logic and policy control, and the Media Resource Function (MRF) with Message Session Relay Protocol (MSRP) functionality responsible for user-plane handling, policy enforcement and charging reporting. This architecture is based on the IMS as defined in 3 GPP R5/R6, 23.228 and 24.229, with the addition of a WeShare client and WeShare server functional entities. The User Equipment (UE) is the terminal equipment containing the weShare XX client or application software (where “XX” designates the weShare service, e.g. image, clip, etc). Every weShare XX service will use a Type A terminal [3 GPP TS 23.060]. 
     The IMS core includes the Proxy-, Interrogating- and Serving-Call Session Control Functions (P-, I-, and S-CSCF respectively) and the Home Subscriber Server (HSS), as defined in 3 GPP R5/R6 TS 23.228 and TS 24.229. The IMS Core performs the following functions:
         Routes the SIP signalling between the UE and the WeShare server;   Terminates the SIP compression from the terminal;   Performs IMS authentication and authorisation;   Maintains the registration state and the SIP session state; and   Reports to the charging system.       

     The UE shall send all SIP messages to the IP address of the P-CSCF (outbound proxy) after resolving the SIP URI of the P-CSCF to an IP address. 
     The SIP AS executes service logic. The MRF with MSRP functionality is responsible for user-plane handling, policy enforcement, and charging reporting. The Circuit Switched (CS) Core contains MSC/VLR, GMSC, HLR and possibly other logical elements according to 3 GPP R5/R6 TS 23.002. 
     The transfer of images and video-clips during a CS call can be done as part of a message session. This message session would be set up at the moment in the CS call where one of the users has expressed willingness to transfer an image. The transfer of images during a CS call can be handled by adapting a message session to carry these images. 
       FIGS. 4   a  to  4   c  illustrates signaling exchanged between two user terminals (UE-A and UE-B) and network nodes, associated with a WeShare Image service. An assumption is that a CS call between the users has already been established. The signaling can be broken down into two main phases, as follows. 
     Phase 1—WeShare Session Set-Up Phase (Signaling Steps  1  to  28  in  FIG. 4   a  and  4   b ) 
     Step  1 . User-A takes a picture and pushes the WeShare button to send the image to User-B. User-A, who has been given an indication of WeShare service availability by the system, shall be able to prepare the image (e.g. by pressing a button to take a photograph with an inbuilt camera) and transmit it to the other party by pressing a WeShare button. The transmitting party&#39;s terminal may generate a query, e.g. confirm image, after presenting the image to its user, requesting that the user presses once again the button to initiate transmission. User-A, who has been given an indication of WeShare service availability, may also be able to select pre-stored content in his/her terminal&#39;s memory and transmit this content to the other party in the conversation. 
     Step  2 . A WeShare IMS session set-up request towards the B-party is initiated. A SIP INVITE is sent to the IMS Core A. The “Request-URI” (e.g. PtS@operator.com) of the SIP INVITE contains the weShare service identity, while the identity of the invited user B shall be included in a body of the message. The SIP INVITE contains an SDP Offer which includes the supported/preferred media content-type (e.g. image/jpeg) and an MSRP URL (msrp-url-A) indicating where the UE-A is willing to receive MSRP requests. Step  3 . The IMS Core A detects an originating trigger and forwards the request to the weShare SIP, AS A. 
     Steps  4 . &amp;  5 . SIP AS A verifies that user A is authorized to use the weShare service feature (e.g. weShare Image). SIP AS A selects an MRF with MSRP capabilities, generates a vXML script (VXML script A) with instructions for the MRF, and sends the SIP INVITE to MRF A. The SIP INVITE includes:
         the invited user B in the Request-URI   HTTP URI including the vXML scrip-id-A   SDP Offer (message msrp-url-A)       

     Steps  6 . &amp;  7 . The MRF A requests the vXML script from SIP AS A, using the script-id-A received in the SIP INVITE. The SIP AS A returns a vXML document including the policy to be enforced. Such policy may include allowed content type (e.g. image, clip, etc.), allowed content size, allowed direction (e.g. send/receive). A protocol such as HTRP may be used for getting such policy information. 
     Step  8 . MRF A reserves MSRP resources and allocates an MSRP-URL (msrp-url-SA). 
     Step  9 . The MRF A behaves as a SIP B2BUA, creates a new SIP dialog, and sends a SIP INVITE to IMS Core B. The SIP INVITE includes:
         the invited user B in the Request-URI   SDP Offer (message msrp-url-SA)       

     Step  10 . The IMS Core B detects a terminating trigger and forwards the request to the weShare SIP AS B.
         Steps  11 . &amp;  12 . The SIP AS B verifies user B is authorized to the weShare service feature (e.g. weShare Image). SIP AS B selects an MRF with MSRP capabilities, generates a VXML script (VXML script B) with instructions for the MRF, and sends the SIP INVITE to MRF B. The SIP INVITE includes:   the invited user B in the Request-URI   HTTP URI including the vXML scrip-id-B   SDP Offer (message msrp-url-SA)       

     Steps  13 . &amp;  14 . The MRF B requests the vXML script from SIP AS B, using the script-id-B received in the SIP INVITE. The SIP AS B returns a vXML document including the policy to be enforced. Such policy may include, allowed content type (e.g. image, clip, etc.), allowed content size, allowed direction (e.g. send/receive). A protocol such as HTRP may be used for getting such policy information. 
     Step  15 . MRF B reserve MSRP resources and allocates an MSRP-URL (msrp-url-SB).
         Step  16 . The MRF B behaves as SIP B2BUA, creates a new SIP dialog, and sends a SIP INVITE to IMS Core B. The SIP INVITE includes:   the invited user B in the Request-URI   SDP Offer (message msrp-url-SB)       

     Step  17 . IMS Core B forwards the SIP INVITE to UE-B. 
     Step  18 . Upon receiving a WeShare IMS session set-up request, the receiving UE will prompt the receiving user to accept or reject the enrichment of the CS call to a WeShare multimedia session (i.e. whether he/she would like to accept the content/image). 
     Steps  19 . &amp;  20 . The receiving user B accepts the request. UE-B sends a SIP  200  OK response to IMS Core B. The response includes an SDP Answer to the SDP Offer received in the INVITE request containing the supported/preferred media content-type (e.g. image/jpeg) and an MSRP URL (msrp-url-B) indicating where the UE-B is willing to receive MSRP requests. 
     Steps  21 . &amp;  22 . The SIP  200  OK is forwarded to MRF B, via SIP AS B. 
     Step  23 . The MRF B sends to IMS Core A an SIP  200  OK including the “msrp-url-SB” 
     Step  24 . &amp;  25 . The SIP  200  OK is forwarded to MRF A, via SIP AS A. 
     Step  26 . The MRF A sends to IMS Core A an SIP  200  OK including the “msrp-url-SA” 
     Step  27 . IMS Core A forwards the SIP  200  OK to UE A. 
     Step  18 . A SIP ACK is sent for each SIP dialog. 
     Phase 2—Image Transfer Phase (Signaling Steps  29  to  41  in  FIG. 4   c ) 
     Step  29 . TCP connections are established between UE-A and MRF-A, MRF-A and MRF-B, MRF-B and UE-B. 
     Step  30 . UE-A sends to MRF A an MSRP SEND, over the established TCP connection, including the image. 
     Steps  31 . &amp;  32 . The MRF A, upon receiving the MSRP SEND, enforces the policy. MRF A behaves as an MSRP back-to-back end point and sends the MSRP SEND to MRF B. 
     Steps  33 . &amp;  34 . The MRF B, upon receiving MSRP SEND, enforces the policy. MRF B behaves as an MSRP “back-to-back end point” and sends the MSRP SEND to UE B 
     Step  35 . UE-B displays the image to User-B. 
     Step  36 . UE B sends to MRF B an MSRP  200  OK response for the MSRP SEND request. 
     Step  37 . MRF B sends to MRF A an MSRP  200  OK response for the MSRP SEND request. 
     Step  38 . MRF A sends to UE A an MSRP  200  OK response for the MSRP SEND request. 
     Step  39 . User A is notified of successful image transfer to User B. 
     Step  40 . &amp;  41 . Upon receipt of the MSRP  200  OK, each MRF produces charging input towards the charging system, for billing of the users. NOTE: in case the content (e.g. image) is segmented in multiple chunks, the MRF generates charging input only when receiving the MSRP  200  OK for the last chunk. 
     The present invention is applicable to applications other than combinational multimedia services such as weShare. Example of other IMS service features to which the invention may be applied are:
     1) Session Based Messaging Group Call. This is an instant messaging conference between more than two users (Session-based Messaging One to Many). A user calls a shared group stored in the network (i.e. a user group that can be used by several users who are typically part of the group, and that is likely to be owned by a single user). This service feature uses MSRP as the user-plane protocol.   2) Push-to-Talk over Cellular (PoC) Instant Group Call. This is a “walky-talky” style 1-to-N call to a shared group. This service feature uses RTCP and RTP as the user plane protocols.   

     For these alternative service features, the SIP INVITE request carrying the IP multimedia service request is forwarded from the IMS Core serving the inviting user A to the SIP AS A hosting the service logic for the requested service and for the inviting user A. Upon receiving the SIP INVITE request, the SIP AS processes it by executing the relevant service logic. When the service request is refused (e.g. due to a screening feature), the SIP AS acts as SIP UA and reject the session attempts, without involving an MRF. When the SIP INVITE request is accepted, the service logic builds a vXML script or an XML document containing the group members that should be invited to the call. The SIP AS acts as a proxy server and transmits the SIP INVITE, including the HTTP URI to be used to retrieve the script/document, to the MRF. The MRF retrieves the script or document, process it, and initiates invitation of the group members to the instant messaging (1) or PoC session (2). The MRF generates N SIP INVITE related to N SIP dialogs, one for each of the invited users. 
     This logic/mechanism may be applied to both originating and terminating features. 
     It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiment without departing from the scope of the present invention. In one application, the MSRP protocol may be used to transfer weShare data between users without the need for intermediate MSRP enabled nodes.