4 System description

26.2373GPPIP Multimedia Subsystem (IMS) based Packet Switch Streaming (PSS) and Multimedia Broadcast/Multicast Service (MBMS) User ServiceProtocolsRelease 17TS

4.1 Introduction

This clause describes the IMS initiated and controlled PSS and MBMS User Service system. It gives a description of the architecture, the role of each new and modified entity and interface.

The description of the PSS system is in 3GPP TS 22.233 [9] and 3GPP TS 26.233 [10]. The description of the MBMS system is in 3GPP TS 23.246 [4].

4.2 Architecture

4.2.1 Non IMS 3GPP PSS and MBMS User Service architecture

Figure 1 describes the Non IMS PSS and MBMS User Service architecture.

Figure 1: Non IMS PSS and MBMS User Service Architecture

The sources consist of all multimedia content in streaming or file form. E.g. live encoders processing in feeds from TV or Music Radio channels.

The PSS server performs control and streaming delivery functions on a Unicast access type.

The BM-SC performs control and streaming/download delivery functions in a hybrid Unicast/Multicast/Broadcast access type.

The core network and RAN enable the mobility, and provides IP connectivity over Unicast/Multicast/Broadcast bearers between the servers and the clients.

The PSS & MBMS client, located in the UE, performs service selection and initiation, receives and present the content to the user.

The PSS client interfaces to the PSS server transparently through the Packet Switch Network. The PSS client can discover the PSS services via multiple means like e.g. browsing. The session description protocol is SDP. The session control protocol is RTSP. The transport protocol is RTP.

The MBMS client interfaces to the BM-SC via layer 3 protocols defined between the UE and the GGSN and the GGSN with the BM-SC (Gmb).

The PSS and MBMS client interfaces via the Radio interface to the RAN and the CN.

The interface between the sources and the PSS server & BM-SC are outside the scope of the present document.

4.2.2 IMS based PSS and MBMS User Service architecture

Figure 2 describes the IMS based PSS and MBMS User Service functional architecture. In addition to PSS and MBMS User Service functions, the IMS core and various functions are added.

Figure 2: IMS based PSS and MBMS functional architecture

In figure 2:

– Solid lines are standard interfaces. E.g. interface between PSS server and UE4.

– Dotted lines are for interfaces for which the protocols in use is out of the scope of the present document. E.g. interface between SSF and BMSC.UPF.

Description of functional entities:

– IM CN Subsystem: IMS Core Network Subsystem as defined in 3GPP TS 23.228 [6].The IM CN Subsystem supports, user registration and authentication, mobility and roaming, control of multimedia sessions, QoS control, Policy control, charging and interworking with circuit switched.

– EPC/PS Core/RAN: Evolved Packet Core, Packet Switch Core Network and Radio Access Network. See 3GPP TS 23.060 [16] and TS 23.401 [30].

NOTE 0: the various packet core networks may offer different levels of support (e.g. the EPC does not support MBMS in 3GPP Release 8).

– UE: The UE contains an GBA/IMS/PSS/MBMS client, which performs service discovery and selection, handles service initiation, modification and termination, receives and present the content to the user. In addition to the procedures specified in this document, the UE shall support the procedures specified in 3GPP TS 24.229 [7] and 3GPP TS 24.109 [22] for the UE functional entity.

– SDF: Service Discovery Function (SDF): this function provides an entry point to SSF for the client to attach to the service provided by the service provider. In addition to the procedures specified in this document, the SDF shall support the procedures specified in 3GPP TS 24.229 [7] for the terminating UA functional entity.

– SSF: Service Selection Function (SSF): this function provides a list of available PSS and MBMS User Services and relevant User Service Description information. It can be personalized to the client’s identity. The SSF shall support Service Announcement functions according to the Xa interface in TISPAN. The PSS portal is for formatting and delivery of PSS Service Description information. The BMSC.IAF and BMSC.USD/A functions are according to 3GPP TS 26.346 [11]. The interface between BMSC.IAF and UE is according to 3GPP TS 26.346 [11] and out of the scope of the present specification. If the User Service Description information exists in a BMSC.USD/A of a "Non-IMS" BM-SC, or in a PSS portal, the SSF takes USD information from them. The SSF may then reformat the USD information before delivery to the UE. The reformat may include information for the IMS UE to build a SIP URI to initiate PSS and MBMS user service.

– SCF: Service Control Function (SCF): it provides service logic and functions required to support execution of such logic. It does service authorization during session initiation and session modification, which includes checking PSS and MBMS user’s service subscription in order to allow or deny access to the service. It selects the relevant PSS and MBMS media functions. In addition to the procedures specified in this document, the SCF shall support the procedures specified in 3GPP TS 24.229 [7]:

– For PSS, the SCF acts as a proxy or B2BUA.

– For MBMS, the SCF acts as a terminating UA.

– BSF: Bootstrapping Server Function (BSF) as defined in 3GPP TS 33.220 [26] and 3GPP TS 24.109 [22] to perform GBA/GAA procedures with the UE. The BSF supports procedures defined in 3GPP TS 33.220 [26] and 3GPP TS 29.109 [x] with the HSS and the BMSC.UPF (see clause 10.4.1) and with the HSS and the SCF (see clause 10.4.2) to enable GBA/GAA procedures.

– HSS: Home Subscriber Server as defined in 3GPP TS 23.002. Contains the IMS User Profile and optionally the GBA User Security Settings (GUSS) defined in 3GPP TS 33.220 [26] and 3GPP TS 29.109 [33]. It also may contain PSS and MBMS User Service specific User and UE data.

– PSS Adapter: this function performs bi-directional protocol translation between SIP and RTSP to offer control of PSS servers as defined in clause 8.2.3.5 and also control of Recording servers as defined in clause 20.1.4. It proxies RTSP messaging from the UE and SIP/RTSP translation towards the PSS server and Recording server. Note that these functions can be incorporated into the SCF, the PSS Server or a new stand-alone entity. In addition to the procedures specified in this document, the PSS Adapter shall support the procedures specified in 3GPP TS 24.229 [7] for the terminating UA functional entity.

– HTTP/SIP adapter: this function correlates SIP session with HTTP incoming requests. In addition to the procedures specified in this document, the HTTP/SIP adapter shall support the procedures specified in 3GPP TS 24.229 [7] for the terminating UA functional entity.

– PCRF: Policy and Charging Rules Function (3GPP TS 23.203 [12]). This function controls the charging and the establishment of resources in the RAN and PS core network.

– PSS Server: Packet Switch Streaming server function as described in 3GPP TS 26.234 [8]. It functionally contains media control and media delivery functions.

– Recording Server: Recording Server function performs live content recording. This function contains two part, to the content resource, it retrieves live streaming content; to PSS Adapter, it act as a RTSP client as defined in section X.1.5.

– HTTP server: this function is described in 3GPP TS 26.234 [8].

– BMSC.UPF: it contains all BMSC User Plane sub-functions.

NOTE 1: The BM-SC Membership function and Proxy and Transport function are defined in 3GPP TS 23.246 [4]. These functions are not described on the architecture in figure 2. The BM-SC Membership function is invoked for the establishment and release of Multicast bearers.

Description of interfaces:

– The interface between the UE and the SSF is used to retrieve service selection information. It is part of the SGi/Gi interface and based on HTTP protocol.

– Gm: This is a SIP based interface between the UE (IMS Client) and the P-CSCF. It is used to forward the SIP service request and response between UE and network.

– The interface between the UE (PSS Client) and the PSS Adapter allows media flow control. It is part of the SGi/Gi interface and based on RTSP protocol.

– The interface between the PSS Server and the UE is for delivery of streaming data. It is part of the SGi/Gi interface and based on RTP and RTCP protocols.

– The interface between the HTTP server and the UE is for delivery of download data. It is part of Sgi/Gi interface and based on HTTP.

– The interface between the BMSC.UPF and the UE is for delivery of streaming data and traffic keys. It is part of the SGi/Gi interface and based on (S)RTP, FLUTE and MIKEY protocols.

– Gmb: This interface is between the BMSC.UPF and the GGSN. The Gmb interface is defined in 3GPP TS 23.246 [4].

– The interface between the PSS Adapter and the PSS Server allows control of the PSS Server. This interface is based on RTSP protocol.

NOTE 2: This interface needs to be named.

– The interface between the PSS Adapter and the Recording Server allows control of the Recording Server. This interface is based on RTSP protocol.

– The interface between the PSS Server and the Recording Server is for delivery of recorded streaming content.

– The interface between the HTTP/SIP adapter and the HTTP server is based on HTTP.

– The interface between the IM CN subsystem and the SCF is an ISC (IMS Service Control) interface based on SIP. The interface between the IM CN subsystem and the PSS adapter is an interface based on SIP protocol.. Both interfaces are used to setup, modify and teardown PSS sessions.

NOTE 3: Under certain conditions this interface between the SCF and the PSS adapter can be implemented as a direct interface (i.e. not going via the IM CN subsystem).

NOTE 4: The interface between the IM CN subsystem and the PSS adapter needs to be named.

– The interface between the IM CN subsystem and the SCF is an ISC (IMS Service Control) interface based on SIP. The interfaces between the IM CN subsystem and the HTTP/SIP adapter is an interface based on SIP.

NOTE 5: Under certain conditions this interface between the SCF and the PSS adapter can be implemented as a direct interface (i.e. not going via the IM CN subsystem).

– This interface between the SSF and the BMSC.UPF is according to 3GPP TS 26.346 [11]. It may be used to carry USD over MBMS bearers.

– The interface between the SDF and the IM CN subsystem is an ISC (IMS Service Control) interface based on SIP protocol.

– The interface between the UE and SCF is used for PSS and MBMS User Service and User Profile configuration. It is equivalent to the Ut interface in TISPAN IPTV.

– The interface between the SCF and the BMSC.UPF is used for security related functions (see clauses 10.4.1 and 10.4.2, respectively).

– The interface between the SCF and the PSS Server is FFS.

– The interface between the UE to the BMSC.SnTF is used for MBMS Associated Delivery procedures as defined in 3GPP TS 26.346 [11]. It is part of the SGi/Gi interface.

– The interface between the UE and the BMSC.KF is used for delivery of the MSK as defined in 3GPP TS 33.246 [5]. It is part of the SGi/Gi interface and based on MIKEY/UDP protocols.

– The interface between the UE and the BMSC.KF may be used for Key Request Functions (see clause 10.4.1).

– The interface between the BSF and the UE is part of the Ub interface defined in 3GPP TS 33.220 [26] and 3GPP TS 24.109 [22] and used for security functionalities.

– The interface between the BSF and the HSS is part of the Zh interface to fetch the Authentication Vectors (AV) and optionally the GBA User Security Settings (GUSS) and defined in 3GPP TS 33.220 [26] and 3GPP TS 29.109 [33].

– The interface between the BSF and the BMSC.UPF (see clause 10.4.1) and between the BSF and the SCF (see clause 10.4.2) is part of the Zn interface to deliver the application security information and defined in 3GPP TS 29.109 [33] and 3GPP TS 33.220 [26].

4.3 IMS based PSS and MBMS US procedures overview

Figure 3 describes the IMS based PSS and MBMS procedures from connection establishment to User Service Description retrieval.

Figure 3: Procedures overview – part 1

Step 1 to 3: are outside the scope of the present document.

Step 4: Service discovery, allows the Client to be informed of the available Service Providers.

Step 5: GBA/GAA bootstrapping procedures, authenticates the User for signalling outside IMS and generates the Long Term Key that will be used during content key management procedures.

Step 6: Retrieval of User Service description, allows the client to obtain the service session information for the selected provider.

Figure 4 describes the IMS based PSS and MBMS procedures from session establishment to content key management.

Figure 4: Procedures overview – part 2

Step 7: Session Establishment, allows the Client to initiate a PSS or MBMS User Service session to receive content.

Step 8: Policy and Charging Control, are procedures performed via the IMS core to setup relevant bearer QoS and charging functions.

Step 9: Content Key Management is necessary to generate and distribute the keys to allow secure delivery of content to the User. At this stage, the delivery session is established and content is delivered to the client.

4.4 PSS and MBMS user profile and UE capabilities

4.4.1 User profile description

The PSS and MBMS user profile data contains all information required to operate PSS and MBMS user services.

The part of the PSS & MBMS user profile used for On Demand (CoD in TISPAN) and Live (BC in TISPAN) services shall be as defined in TISPAN TS 183 063, Annex C.

The part of the PSS & MBMS user profile used for Parental Control Service shall be as defined in Annex M.

4.4.2 UE capabilities

A set of PSS and MBMS UE capabilities is required to personalize and operate PSS and MBMS user services. These capabilities are described in 2 documents:

– The PSS and MBMS UE Capabilities XML document defined in Annex G.

– The RDF/XML document for the PSS base vocabulary specified in Annex F of TS 26.234 [8].

These 2 documents are sent during the Service Discovery procedure. See clause 6.

4.4.3 Storage location

PSS and MBMS user profile and UE capabilities information may be stored in the following locations:

– Application Server functions.

– In a stand-alone server associated with one or more Application Server functions.

– In the HSS as transparent data associated to these Application Server functions.

The first and second options are recommended for data to be accessed by 3rd party application server functions. In the first and second case the Application Server function or the stand-alone server may exhibit the behaviour of an XDMS.

User data stored in the HSS can be accessed by Application Servers at the Sh reference point.

A subset of PSS and MBMS user-profile information may be accessed from the User Equipment at the Ut reference point.

For the purpose of personalized service selection, the SSF may need to access user data.

In the case when such user data is stored in the HSS, it can be accessed by the SSF at the Sh reference point when the SSF is in the same domain.

On the contrary, when such user data is stored in the AS or in a stand alone server associated with one or more application servers or if the SSF in not in the same domain as the HSS, the user data can be accessed by the SSF using an interface that is out of scope for this release.

The SSF may also request notification of user data updates.