Patent Publication Number: US-2009228939-A1

Title: Time-shift tv service establishment method and time-shift tv media function entity

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2008/071383, filed on Jun. 20, 2008, which claims the priority of Chinese Patent Application No. 200710129329.8, filed on Jul. 4, 2007, and entitled “TIME-SHIFT TV SERVICE ESTABLISHMENT METHOD AND TIME-SHIFT TV MEDIA FUNCTION ENTITY”, both of which are incorporated herein by reference in their entirety. 
    
    
     FIELD OF THE TECHNOLOGY 
     The present disclosure relates to the communication field, and more particularly to a time-shift TV (TsTV) service establishment method and a time-shift TV media function (TsTV MF) entity. 
     BACKGROUND 
     The time-shift television (TsTV) service is a newly-emerging streaming media service. Currently, a solution based on an existing IP network is shown in  FIG. 1 , in which the system is constituted by a headend  101 , a middleware  102 , a video on demand (VOD) system  103 , a set-top box (STB)  104 , etc. 
     In the existing system, the TsTV service is basically realized as follows. 
     First, the STB  104  obtains a program menu from the middleware  102 , a multicast group for playing a selected program based on the program menu is added in the STB  104 , so as to receive the TV program, and the TV program is sent by means of multicasting. 
     If a user selects to pause or fast backward (also known as reverse) the TV program, the STB  104  sends a request to the middleware  102 . The middleware  102  and the VOD system  103  interactively position a corresponding unicast program source and transmit its address to the middleware  102 . Then, the middleware  102  returns the address to the STB  104 . 
     Afterwards, the STB  104  obtains a unicast program stream from the VOD system  103 , and controls the TV program through the real time streaming protocol (RTSP). If the user selects to fast forward and catch up with the live program, the STB  104  is once again switched to the multicast receiving state. 
     During the implementation of the present disclosure, it was found that the above solution is directed to the existing Internet Protocol (IP) network, and the TsTV service is realized by adopting the Hypertext Transfer Protocol/Real Time Streaming Protocol (HTTP/RTSP) and the like as a service request or control signaling. However, for an IP multimedia subsystem (IMS) that is in the process of rapid development, the prior art does not explicitly provide any implementation to realize the TsTV service in the IMS system. 
     SUMMARY 
     Accordingly, the present disclosure is directed to a time-shift TV (TsTV) service establishment method and a time-shift TV media function (TsTV MF) entity, which are configured to realize TsTV services in an IMS network. 
     In an embodiment of the present disclosure, a TsTV service establishment method is provided. The method includes the following steps. A TsTV MF entity receives a media negotiation including content delivery channel information and content control channel information initiated by a terminal, establishes a transmission connection with the terminal according to a media negotiation result, receives a media playing request sent from the terminal through the transmission connection, and sends media information corresponding to the media playing request to the terminal through a content delivery channel established according to the content delivery channel information. 
     In an embodiment of the present disclosure, a TsTV service establishment method is provided. The method includes the following steps. A TsTV MF entity receives a media negotiation including content control channel information initiated by a terminal, establishes a transmission connection with the terminal according to a media negotiation result, receives a request message for content delivery channel information sent from the terminal through the transmission connection, returns a response message including the content delivery channel information to the terminal, receives a media playing request sent from the terminal, and sends media information corresponding to the media playing request to the terminal through a content delivery channel established according to the content delivery channel information. 
     In an embodiment of the present disclosure, a TsTV service establishment method is provided. The method includes the following steps. A service control function (SCF) receives operation information reported by a terminal, and sends a session initialization request message to a TsTV MF entity. The TsTV MF entity initiates a media negotiation request including content control channel information and content delivery channel information, establishes a transmission connection with the terminal according to a media negotiation result, receives a media playing request sent from the terminal through the transmission connection, and sends media information corresponding to the media playing request to the terminal through a content delivery channel established according to the content delivery channel information. 
     In an embodiment of the present disclosure, a TsTV service establishment method is provided. The method includes the following steps. An SCF receives a session update request message including TsTV service information sent from a terminal, and sends a session initialization request message to a TsTV MF entity. The TsTV MF entity initiates a media negotiation request including content control channel information, establishes a transmission connection with the terminal according to a media negotiation result, receives a media playing request sent from the terminal through the transmission connection, returns a response message including content delivery channel information to the terminal, and afterwards sends media information corresponding to the media playing request to the terminal through a content delivery channel established according to the content delivery channel information. 
     In an embodiment of the present disclosure, a TsTV service establishment method is provided. The method includes the following steps. An SCF receives a session initialization request message including a channel ID or including a channel ID and program position information sent from a terminal, determines a content delivery type according to the session initialization request message, and performs corresponding processes according to the content delivery type. 
     In an embodiment of the present disclosure, a TsTV MF entity is provided. The TsTV MF entity includes: a request message receiving unit configured to receive a request message including content delivery channel information and content control channel information sent from a terminal; a channel establishment control unit configured to establish a transmission connection with the terminal according to the content control channel information; a request receiving unit configured to receive a media playing request sent from the terminal through the transmission connection; and a media information returning unit configured to return media information corresponding to the media playing request to the terminal through a content delivery channel established according to the content delivery channel information. 
     Alternatively, the TsTV MF entity includes: a receiving unit configured to receive a request message including content control channel information sent from a terminal; a channel establishment control unit configured to establish a transmission connection with the terminal according to the content control channel information; a message transmission unit configured to receive a request message for content delivery channel information sent from the terminal through the transmission connection, and return a response message including the content delivery channel information to the terminal; a request receiving unit configured to receive a media playing request sent from the terminal; and a media information returning unit configured to return media information corresponding to the media playing request to the terminal through a content delivery channel established according to the content delivery channel information. 
     In an embodiment of the present disclosure, a TsTV service triggering method is provided. The method includes the following steps. A terminal sends operation information and/or TsTV service information to an SCF according to an operation of a user, and the SCF triggers a TsTV service according to the operation information and/or TsTV service information. 
     In an embodiment of the present disclosure, a TsTV MF entity receives a request message including content delivery channel information and content control channel information sent from a terminal, so that the TsTV MF entity is enabled to establish a content control channel for transmitting control signaling with the terminal according to the received content control channel information, and establish a content delivery channel for transmitting real-time streaming media with the terminal according to the content delivery channel information, thereby realizing TsTV services in an IMS system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural view of a TsTV service system in the prior art; 
         FIG. 2  is a flow chart of a TsTV service establishment method according to a first embodiment of the present disclosure; 
         FIG. 3  is a flow chart of a TsTV service establishment method according to a second embodiment of the present disclosure; 
         FIG. 4  is a flow chart of a TsTV service establishment method according to a third embodiment of the present disclosure; 
         FIG. 5  is a flow chart of a TsTV service establishment method according to a fourth embodiment of the present disclosure; 
         FIG. 6  is a flow chart of a TsTV service establishment method according to a fifth embodiment of the present disclosure; 
         FIG. 7  is a schematic view of a TsTV MF entity according to a first embodiment of the present disclosure; and 
         FIG. 8  is a schematic view of a TsTV MF entity according to a second embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In an embodiment of the present disclosure, a TsTV service establishment method and a TsTV MF entity are provided, which are configured to realize TsTV services in an IMS system. 
     The TsTV services may be classified into the following two types according to the manner that a user enters a TsTV state. 
     1) Direct time-shift mode: when watching a live TV (LTV), the user presses a pause or backward (also known as reverse) key to switch from the live to the time-shift state. 
     2) Time-shift channel mode: an electronic program guide (EPG) provides time-shift channel information, and the user can select to watch a time-shift video program. 
     The TsTV service processing can be divided into the following four sub-processes. 
     A. Service establishment process: the service establishment process primarily refers to an initial establishment process of a service. 
     B. VCR operating process: when watching the TsTV service, the user may perform a VCR operation (also known as Trick Mode), for example, pause, fast forward, fast backward, and jump. 
     C. Handover process between unicast and multicast after the service is established: in an IMS-based IPTV system, the LTV generally transmits media streams by means of multicasting. The TsTV service generally transmits media streams by means of unicasting in a non-latest playing state (the time-shift content is being played), and generally transmits the media streams by means of multicasting in a latest playing state (the live content is being played). After a TsTV service session is established, the user can perform a VCR operation, for example, fast forward or jump to a latest playing point, thereby triggering the handover between multicast and unicast. 
     D. Service release process. 
     A general introduction of the TsTV service is given above, and the TsTV service establishment method in an embodiment of the present disclosure is described in detail below. Specifically, according to a user access mode, the TsTV service establishment method provided in the embodiments of the present disclosure can be classified into the following two types. 
     1. Direct Time-Shift Mode 
     In this mode, the TsTV service establishment method can be subdivided into the following four embodiments. 
     1. A content delivery channel and a content control channel are established at the same time. 
     Referring to  FIG. 2 , in a first embodiment of the present disclosure, the TsTV service establishment method includes the following steps. 
     In Step  201 , a user requests to pause a program. 
     For example, the user watches an LTV in a multicast delivery mode, and the user requests a pause when watching the program. 
     As another example, the user requests a pause when watching the LTV supporting a VCR operation (or Trick Mode). 
     In Step  202 , a terminal sends a request to a basic control function (BCF) for quitting a multicast group. 
     The terminal records playing position information of the media, and sends a report about leaving the multicast group to a multicast point that provides live media streams. In this embodiment, it is unnecessary to send a report message about leaving the multicast group when being based on Internet Gateway Message Protocol (IGMP) Version 1.0, and it is necessary to send a report message about leaving the multicast group when being based on IGMP Version 2.0, so that this step is optional. 
     In Step  203 , the user requests to resume playing the TV program. 
     For example, the user presses a play key on a remote control handle to request to resume playing the TV program. As the user no longer receives the multicast media streams at this time, the TsTV service is required to enable the user to resume watching the TV program. 
     In Step  204 , the terminal sends a session update request. 
     The terminal sends a session update request to a network (IMS Core), in which the request carries media description information (Streaming Download Project (SDP) Offer 1 ) about the content delivery channel and the content control channel (for example, Transport Control Protocol (TCP) connection). 
     In this embodiment, the multicast media streams of the original LTV may be stored or deactivated according to the actual requirements. 
     In Step  205 , the session update request is forwarded. 
     After receiving the session update request message from the terminal, the IMS Core forwards the received session update request to a service control function (SCF) that provides the LTV according to IMS Core signaling routing rules defined according to the 3 rd  Generation Partnership Project (3GPP)_IMS specification. 
     In Step  206 , a session initialization request is initiated. 
     After receiving the session update request, the SCF determines whether the user is requesting the TsTV service or not according to the content of the session update request message, which is determined based on the references of service ID information carried in the Session Initiation Protocol (SIP) header field of the session update request message or the control channel information in the SDP message body. If it is determined that the user is requesting the TsTV service, the SCF initiates a new session initialization request to the TsTV MF entity that provides the TsTV services, in which the session initialization request message carries media description information (SDP Offer 2 ) about the content delivery channel and the content control channel. 
     In this embodiment, the message routing mode between the SCF and the TsTV MF entity is not limited. For example, the message may be routed or forwarded without passing through the IMS Core. 
     In Step  207 , a session initialization response message is returned. 
     After receiving the request, the TsTV MF entity that provides a time-shift service media resource establishes an SIP session and an RTSP session, generates a session ID of the RTSP session, distributes the media resource required by the TsTV service, returns a session initialization response message (200 OK) carrying media Answer information (SDP Answer 2 ) about the content delivery channel and the content control channel, and waits for the establishment of the TCP connection. 
     In Step  208 , a session update response message is returned. 
     The SCF sends a session update response message (200 OK) to the IMS Core, in which the message carries media Answer information (SDP Answer 1 ) about the content delivery channel and the content control channel. 
     In Step  209 , the session update response message is forwarded. 
     The IMS Core forwards the session update response message (200 OK) to the terminal, in which the message carries the media Answer information (SDP Answer 1 ) about the content delivery channel and the content control channel. 
     In steps  210  to  212 , the terminal returns an acknowledgement (ACK) message. 
     After receiving the session update response message, the terminal stores the critical information in the response message, for example, the media description information and session ID information. If a SIP reINVITE mechanism is adopted, the terminal sends a response ACK message to the IMS Core, and the message is transmitted to the TsTV MF entity via the SCF. 
     In Step  213 , a bearer connection is established. 
     In the above steps, the terminal, SCF, and TsTV MF entity perform a media negotiation through interaction of the content delivery channel information and the content control channel information. 
     The terminal establishes a transmission connection (for example, TCP connection) that bears an RTSP with the TsTV MF entity according to the media negotiation result. 
     In Step  214 , the terminal sends a media playing request. 
     The terminal sends a playing request message (RTSP PLAY) to the TsTV MF entity through the content control channel. The playing request message carries parameter information such as a session ID and media position information (for example, absolute time for playing). 
     In Step  215 , a media playing response is returned. 
     The TsTV MF entity sends a playing message (RTSP 200 OK) to the terminal through the content control channel. 
     In Step  216 , the media streams are transmitted. 
     The TsTV MF entity sends the streaming media content to the terminal through the content delivery channel. 
     In this embodiment, the pause and resume operations of the user are used as examples to illustrate the implementation of the TsTV service, and it is to be understood that other operations, for example, fast forward or slow forward, may also be adopted and the specific implementations thereof are similar. 
     In this embodiment, steps  210  to  215  are optional and can be selected according to actual requirements. 
     In this embodiment, as the terminal sends the session update request message carrying the content delivery channel information and the content control channel information, the TsTV MF establishes the content control channel and the content delivery channel according to the two parameters, thereby realizing TsTV services in an IMS system. 
     2. The content delivery channel and the content control channel are established independently. 
     Referring to  FIG. 3 , in a second embodiment of the present disclosure, the TsTV service establishment method includes the following steps. 
     In Step  301 , a user requests to pause a program. 
     For example, the user watches an LTV in a multicast delivery mode, and requests a pause when watching the program. 
     As another example, the user requests a pause when watching the LTV supporting a VCR operation (or Trick Mode). 
     In Step  302 , a terminal sends a request to a BCF for quitting a multicast group. 
     The terminal records playing position information of the media, and sends a report about leaving the multicast group to a multicast point that provides live media streams. In this embodiment, it is unnecessary to send a report message about leaving the multicast group when being based on IGMP Version 1.0, and it is necessary to send a report message about leaving the multicast group when being based on IGMP Version 2.0, so that this step is optional. 
     In Step  303 , the user requests to resume playing the TV program. 
     For example, the user presses a play key on a remote control handle to request to resume playing the TV program. As the user is not receiving the multicast media streams at this time, the TsTV service is required to enable the user to resume watching the TV program. 
     In Step  304 , the terminal initiates a session update request. 
     In this embodiment, the content of the session update request may have the following two circumstances. 
     A. The session update request sent by the terminal carries a content object ID of the time-shift program (for example, RTSP Uniform Resource Identifier (URI) carried in the Request-URI header field of the RTSP). 
     B. The session update request sent by the terminal does not carry the content object ID of the time-shift program. 
     In this step, the initiated session update request carries media description information (SDP Offer 1 ) about the content control channel, in which the information may carry the content object ID of the time-shift program. 
     In this embodiment, the multicast media streams of the original LTV may be stored or deactivated according to actual requirements. 
     In Step  305 , the session update request is forwarded. 
     After receiving the session update request message from the terminal, the IMS Core forwards the received session update request of the terminal to an SCF that provides the LTV according to IMS Core signaling routing rules defined based on the 3GPP IMS specification. 
     In Step  306 , a session initialization request is initiated. 
     After receiving the session update request, the SCF determines that the user is requesting the TsTV service according to the content of the session update request message, and initiates a new session initialization request to the TsTV MF entity that provides the TsTV service. The session initialization request message carries media description information (SDP Offer 2 ) about the content control channel. 
     In Step  307 , a session initialization response is returned. 
     After receiving the request, the TsTV MF entity that provides a time-shift service media resource establishes a SIP session. 
     In the above embodiment A, the TsTV MF entity establishes an RTSP session at the same time, generates a session ID of the RTSP session, and distributes the media resource required by the TsTV service. 
     In the above embodiment B, the TsTV MF entity does not establish an RTSP session, and instead carries the content object ID in the response message. 
     Afterwards, a session initialization response message (200 OK) carrying media Answer information (SDP Answer 2 ) about the content control channel is returned, and the TsTV MF entity waits for the establishment of the TCP connection. 
     In Step  308 , a session update response message is returned. 
     The SCF sends a session update response message (200 OK) carrying media Answer information (SDP Answer 1 ) about the content control channel to the IMS Core. 
     In Step  309 , the session update response message is forwarded. 
     The IMS Core forwards the session update response message (200 OK) carrying media Answer information (SDP Answer 1 ) about the content control channel to the terminal. 
     In steps  310  to  312 , the terminal returns an ACK message. 
     After receiving the session update response message, the terminal stores critical information in the response message, for example, media description information of the content control channel and session ID. If a SIP reINVITE mechanism is adopted, the terminal sends a response ACK message to the IMS Core, and the message is transmitted to the TsTV MF entity via the SCF. 
     In Step  313 , a bearer connection is established. 
     In the above steps, the terminal, SCF, and TsTV MF entity perform a media negotiation through interaction of the content control channel information. 
     The terminal establishes a transmission connection (for example, TCP connection) that bears an RTSP with the TsTV MF entity according to the media negotiation result. 
     In Step  313   b , the media description information is acquired. 
     The terminal requests the TsTV MF entity for the media description information about the content delivery channel through the established content control channel, for example, sending an RTSP SUBSCRIBE request. The TsTV MF entity returns a response message (RTSP 200 OK) carrying media description information about the content delivery channel to the terminal 
     In Step  314 , a session update request is initiated. 
     The terminal once again sends a session update request to the IMS Core, and a media row of the content delivery channel (SDP Offer 3 ) is newly added in the request message. As for the above circumstance B, the content object ID information is further added in a media row of the requested content control channel. 
     In Step  315 , the session update request is forwarded. 
     After receiving the session update request message from the terminal, the IMS Core routes the received session update request of the terminal to an SCF according to IMS Core signaling routing rules defined based on the 3GPP IMS specification. 
     In Step  316 , the session update request is sent. 
     After receiving the session update request, the SCF initiates the session update request to the corresponding TsTV MF entity. The session update request message carries the media row of the content control channel and the media row of the content delivery channel (SDP Offer 4 ). 
     In Step  317 , a session update response is returned. 
     After receiving the request, the TsTV MF entity distributes the media resource required by the TsTV service. As for the above circumstance B, the TsTV MF entity establishes an RTSP session, and carries session ID information in the response message. Then, the TsTV MF entity returns a session update response message (200 OK) carrying media Answer information (SDP Answer 4 ) about the content control channel. 
     In Step  318 , a session update response is returned. 
     The SCF sends a session update response message (200 OK) carrying media Answer information (SDP Answer 3 ) about the content delivery channel and the content control channel to the IMS Core. 
     In Step  319 , the session update response is forwarded. 
     The IMS Core forwards the session update response message (200 OK) carrying media Answer information (SDP Answer 3 ) about the content delivery channel and the content control channel to the terminal. 
     In steps  320  to  322 , the terminal returns an ACK message. 
     After receiving the session update response message, the terminal stores critical information in the response message, for example, media description information and session ID information. If a SIP reINVITE mechanism is adopted, the terminal sends a response ACK message to the IMS Core, and the message is transmitted to the TsTV MF entity via the SCF. 
     In Step  323 , the terminal sends a media playing request. 
     The terminal sends a media playing request message (RTSP PLAY) carrying parameter information such as a session ID and media position information (for example, absolute time for playing) to the TsTV MF entity through the content control channel. 
     In Step  324 , a media playing response is returned. 
     The TsTV MF entity sends a playing message (RTSP 200 OK) to the terminal through the content control channel. 
     In Step  325 , media streams are transmitted. 
     The TsTV MF entity sends the streaming media content to the terminal through the content delivery channel. 
     In this embodiment, the pause and resume operations of the user are taken as examples to illustrate the implementation of the TsTV service, and it is to be understood that other operations, for example, fast forward or slow forward, may also be adopted and the specific implementations thereof are similar. 
     The difference between the TsTV service establishment method of this embodiment and that of the first embodiment is that, in this embodiment, the content control channel and the content delivery channel are not established at the same time. Instead, the content control channel is established first, and then the media description information about the content delivery channel is acquired via the content control channel, so as to establish the content delivery channel accordingly. Therefore, the flexibility of the TsTV service establishment method according to the embodiment of the present disclosure is enhanced. 
     3. The operation information is reported to trigger the TsTV service. 
     Referring to  FIG. 4 , in a third embodiment of the present disclosure, the TsTV service establishment method includes the following steps. 
     In Step  401 , a user requests to pause a program. 
     For example, the user watches an LTV in a multicast delivery mode, and requests a pause when watching the program. 
     As another example, the user requests a pause when watching the LTV supporting a VCR operation (or Trick Mode). 
     In Step  402 , a terminal sends a request to a BCF for quitting a multicast group. 
     The terminal records playing position information of the media, and sends a report about leaving the multicast group to a multicast control point that provides multicast media streams. In this embodiment, it is unnecessary to send a report message about leaving the multicast group when being based on IGMP Version 1.0, and it is necessary to send a report message about leaving the multicast group when being based on IGMP Version 2.0, so that this step is optional. 
     In Step  403 , the user requests to resume playing the TV program. 
     For example, the user presses a play key on a remote control handle to request to resume playing the TV program. As the user no longer receives the multicast media streams at this time, the TsTV service is required to enable the user to resume watching the TV program. 
     In Step  404 , an operation report request is sent. 
     In this embodiment, the following two operation requests may be reported. 
     A. The terminal reports original information about a key (for example, key number): the terminal reports the original information about the key/operation of the user to the SCF, and then the SCF resolves the definition of the key, combines with the service context, and determines the service request information of the user. 
     B. The terminal reports VCR operation information (for example, information carrying RTSP parameters of Scale/Range): the terminal needs to convert the key/operation of the user into the VCR operation information, and reports the VCR operation information to the SCF. 
     The terminal may report the information to the SCF in various signaling implementation manners, including but not limited to, SIP Message/Info mechanism, SIP Subscribe/Notify mechanism, non-SIP mechanism, and the like. 
     In Step  405 , the establishment of the TsTV service is triggered. 
     The SCF determines that the user requests the TsTV service according to a service processing logic (the user requests to pause/play when watching the LTV), and thus triggers the establishment of the TsTV service. 
     In Step  406 , a session initialization request is initiated. 
     The SCF sends a session initialization request to the TsTV MF entity, in which the request does not include an SDP message body. 
     In Step  407 , a session initialization response message is returned. 
     After receiving the session initialization request, the TsTV MF entity establishes a SIP session, and returns a session initialization response message (200 OK) to the SCF. The response carries media description information (SDP Offer 1 ) about a content control channel and a content delivery channel. 
     In Step  408 , a session update request is sent. 
     After receiving the session initialization response message from the TsTV MF entity, the SCF sends a session update request to the IMS Core, in which the request carries media description information (SDP Offer 2 ) about the content control channel and the content delivery channel. 
     In Step  409 , the session update request is forwarded. 
     The IMS Core forwards the received session update request to the terminal according to IMS signaling routing rules. 
     In Step  410 , the terminal returns a session update response. 
     After receiving the session update request message from the network, the terminal returns a session update response message to the IMS Core according to capabilities of the terminal and service processing rules, in which the response message carries media Answer information (SDP Answer 2 ) about the content control channel and the content delivery channel. 
     In Step  411 , the session update response is forwarded. 
     The IMS Core forwards the received session update response message to the SCF according to the IMS signaling routing rules. 
     In steps  412  to  413 , a session update ACK is sent. 
     The SCF returns a session update ACK to the terminal, and the message is routed by the IMS Core. 
     In Step  414 , a session initialization ACK is sent. 
     The SCF constructs a session initialization ACK message, including media Answer information (SDP Answer 1 ) about the content control channel and the content delivery channel, based on the session update response message received from the terminal. 
     In Step  415 , a subsequent process is performed. 
     The subsequent process includes the following steps. 
     A. The terminal sends a media playing request. 
     The terminal sends a media playing request message (RTSP PLAY) to the TsTV MF entity through the content control channel, in which the message carries parameter information such as a session ID and media position information (for example, absolute time for playing). 
     B. A media playing response is returned. 
     The TsTV MF entity sends a playing message (RTSP 200 OK) to the terminal through the content control channel. 
     C. The media streams are transmitted. 
     The TsTV MF entity sends the streaming media content to the terminal through the content delivery channel. 
     In this embodiment, the terminal triggers the TsTV service through reporting the operation information, and the specific type of the operation information is determined according to actual requirements, thereby improving the flexibility of the TsTV service establishment method in the embodiment of the present disclosure. 
     4. The service information is reported to trigger the TsTV service. 
     Referring to  FIG. 5 , in a fourth embodiment of the present disclosure, the TsTV service establishment method includes the following steps. 
     In Step  501 , a user requests to pause a program. 
     For example, the user watches an LTV in a multicast delivery mode, and requests a pause when watching the program. 
     As another example, the user requests a pause when watching the LTV supporting a VCR operation (or Trick Mode). 
     In Step  502 , a terminal sends a request to a BCF for quitting a multicast group. 
     The terminal records playing position information of the media, and sends a report about leaving the multicast group to a multicast control point that provides multicast media streams. In this embodiment, it is unnecessary to send a report message about leaving the multicast group when it is based on IGMP Version 1.0, and it is necessary to send a report message about leaving the multicast group when it is based on IGMP Version 2.0, so that this step is optional. 
     In Step  503 , the user requests to resume playing the TV program. 
     For example, the user presses a play key on a remote control handle to request to resume playing the TV program. As the user no longer receives the multicast media streams at this time, the TsTV service is required to enable the user to resume watching the TV program. 
     In Step  504 , a session update request is initiated. 
     The terminal determines that the user is requesting the TsTV service according to the current service context and the VCR operation of the user, and sends a session update request to the IMS Core. The request does not include the SDP message body, but carries the TsTV service information. The manner for identifying that the user is requesting the TV service includes, but not limited to, using a service ID. 
     In Step  505 , the session update request is forwarded. 
     The IMS Core forwards the received session update request to the SCF according to IMS signaling routing rules. 
     In Step  506 , a session initialization request is initiated. 
     After receiving the session update request message from the terminal, the SCF determines to trigger the TsTV service according to the TsTV service information carried in the request, and sends a session initialization request to the TsTV MF entity. The request does not include an SDP message body. 
     In Step  507 , a session initialization response is returned. 
     After receiving the session initialization request, the TsTV MF entity establishes a session and returns a session initialization response message, including media description information (SDP Offer 1 ) about a content control channel and a content delivery channel. 
     In Step  508 , a session update response is returned. 
     The SCF constructs a session update response message and a message body based on the received session update response message and the service context information. The session update response message carries media description information (SDP Offer 2 ) about the content control channel and the content delivery channel. 
     In Step  509 , the session update response is forwarded. 
     The IMS Core forwards the received session update response message to the terminal according to the IMS signaling routing rules. 
     In Step  510 , a session update ACK is returned. 
     After receiving the session update response message from the network, the terminal returns a session update ACK message to the IMS Core according to capabilities of the terminal and service processing rules, in which the session update ACK message carries media Answer information (SDP Answer 2 ) about the content control channel and the content delivery channel. 
     In Step  511 , the session update ACK is forwarded. 
     The IMS Core forwards the received session update ACK message to the SCF according to the IMS signaling routing rules. 
     In Step  512 , a session initialization ACK is returned. 
     The SCF constructs a session initialization ACK message according to the received session update ACK message and the service context information. The session initialization ACK message carries media Answer information (SDP Answer 1 ) about the content control channel and the content delivery channel. 
     In Step  513 , a subsequent process is performed. 
     The subsequent process includes the following steps. 
     A. The terminal sends a media playing request. 
     The terminal sends a media playing request message (RTSP PLAY) to the TsTV MF entity through the content control channel, in which the message carries parameter information such as a session ID and media position information (for example, absolute time for playing). 
     B. A media playing response is returned. 
     The TsTV MF entity sends a playing message (RTSP 200 OK) to the terminal through the content control channel. 
     C. The media streams are transmitted. 
     The TsTV MF entity sends the streaming media content to the terminal through the content delivery channel. 
     In this embodiment, the terminal triggers the TsTV service through reporting the service information. In particular, the terminal converts the key/operation of the user into service request information according to the current service context, for example, when the LTV service is undergoing, the terminal determines that the user is requesting the TsTV service, so that the terminal reports the time-shift service request information to the SCF, etc. Thus, the SCF invokes a proper service processing logic according to the service request information, for example, triggering the establishment of the TsTV service, so as to improve the flexibility of the TsTV service establishment method in the embodiment of the present disclosure. 
     2. Time-Shift Channel Mode 
     Referring to  FIG. 6 , in a fifth embodiment of the present disclosure, the TsTV service establishment method includes the following steps. 
     In Step  601 , an EPG is browsed. 
     The user browses an EPG menu, enters a time-shift channel sub-menu, selects a specific time-shift channel (i.e., requesting to start playing from a previous playing position at which the user quit or paused the program or from the latest position) and/or designates a playing program or playing position, and requests to watch the program. 
     In Step  602 , a session initialization request is initiated. 
     The terminal sends a session initialization request to the IMS Core. The session initialization request carries a channel ID and program position information, but does not include media description information (i.e., does not include SDP) about a content control channel or a content delivery channel. 
     In Step  603 , the session initialization request is forwarded. 
     The IMS Core forwards the session initialization request from the terminal to the SCF according to routing rules described in the 3GPP IMS specification. 
     In Step  604 , the session initialization request is initiated. 
     After receiving the session initialization request message, the SCF identifies that the user is requesting the TsTV service according to information carried in the request, and establishes a session. The user requests to watch the time-shift channel, but does not designate the playing program or position information. The SCF determines whether the media delivery channel adopts a multicast or unicast mode according to the stored user service information (for example, the information about the previous position where the user leaves this channel) and/or local policies. 
     If the current live content needs to be sent to the user, the delivery mode of multicast media streams is adopted. The SCF sends a session initialization response message to the IMS Core (i.e., Step  606 ), in which the message carries media description information about the multicast media streams. The subsequent establishment process is similar to that of the existing LTV service, and the details thereof are not described herein again. 
     If the content at a previous time point needs to be sent to the user, the delivery mode of unicast media streams is adopted. The SCF sends a session initialization request message to the TsTV MF entity that provides the TsTV media resource, in which the message does not include the media description information. Step  605  is then performed. 
     In Step  605 , a session initialization response is returned. 
     The TsTV MF entity returns a session initialization response message including media description information (SDP Offer 1 ) about a content control channel and a content delivery channel to the SCF 
     In Step  606 , a session initialization response is returned. 
     The SCF constructs a session initialization response message according to the session initialization response message of the TsTV MF entity. The session initialization response message of the SCF carries media description information (SDP Offer 2 ) about the content control channel and the content delivery channel, and then the SCF sends the session initialization response message to the IMS Core. 
     In Step  607 , the session initialization response is forwarded. 
     The IMS Core forwards the session initialization response message to the terminal according to routing rules described in the 3GPP IMS specification. 
     In the combination of steps  608  and  609  or the combination of steps  608 ,  609 , and  610 , the session initialization response is returned. 
     When Step  605  is performed in the above process, Step  610  needs to be performed. 
     The terminal sends a session initialization ACK message to the SCF through the IMS Core. The session initialization ACK message carries media Answer information (SDP Answer 2 ) about the content control channel and the content delivery channel, and then the SCF forwards the message including media Answer information (SDP Answer 1 ) to the TsTV MF. 
     In steps  611 A and  612 A, when the multicast media streams are required, the terminal adds to a multicast group, and a BCF sends the multicast media streams to the terminal. 
     In steps  611 B to  613 B, when the unicast media streams are required, the content control channel is established, and a media playing request is initiated to the TsTV MF entity. The TsTV MF entity returns a playing response, and sends the media streams to the terminal. 
     In this embodiment, the implementation of the TsTV service in the time-shift channel mode is illustrated, thereby further improving the flexibility of the TsTV service establishment method in the embodiment of the present disclosure. 
     The device embodiments of the present disclosure are illustrated below. Referring to  FIG. 7 , in a first embodiment of the present disclosure, a TsTV MF entity includes a request message receiving unit  701 , a channel establishment control unit  702 , a request receiving unit  703 , and a media information returning unit  704 . 
     The request message receiving unit  701  is configured to receive a request message carrying content delivery channel information and content control channel information sent from a terminal. 
     The channel establishment control unit  702  is configured to establish a transmission connection with the terminal according to the content control channel information. 
     The request receiving unit  703  is configured to receive a media playing request sent from the terminal through the transmission connection. 
     The media information returning unit  704  is configured to send media information corresponding to the media playing request to the terminal through a content delivery channel established according to the content delivery channel information. 
     Referring to  FIG. 8 , in a second embodiment of the present disclosure, the TsTV MF entity includes a receiving unit  801 , a channel establishment control unit  802 , a message transmission unit  803 , a request receiving unit  804 , and a media information returning unit  805 . 
     The receiving unit  801  is configured to receive a request message carrying content control channel information sent from a terminal. 
     The channel establishment control unit  802  is configured to establish a transmission connection with the terminal according to the content control channel information. 
     The message transmission unit  803  is configured to receive a request message for the content delivery channel information sent from the terminal through the transmission connection, and return a response message carrying the content delivery channel information to the terminal. 
     The request receiving unit  804  is configured to receive a media playing request sent from the terminal. 
     The media information returning unit  805  is configured to send media information corresponding to the media playing request to the terminal through a content delivery channel established according to the content delivery channel information. 
     Those of ordinary skill in the art should understand that, all or a part of the steps of the method according to the embodiments of the present disclosure can be implemented by relevant hardware under the instruction of a program. The program may be stored in a computer readable storage medium. When the program is executed, the following steps are performed. The TsTV MF entity receives a media negotiation carrying content delivery channel information and content control channel information initiated by a terminal, establishes a transmission connection with the terminal according to the media negotiation result, receives a media playing request sent from the terminal through the transmission connection, and sends media information corresponding to the media playing request to the terminal through a content delivery channel established according to the content delivery channel information. 
     The storage medium may be a ROM, a magnetic disk, or an optical disk. 
     In the embodiments of the present disclosure, the TsTV MF entity receives a request message carrying content delivery channel information and content control channel information sent from the terminal, so that the TsTV MF entity is enabled to establish a content control channel for transmitting control signaling with the terminal according to the received content control channel information, and establish a content delivery channel for transmitting real-time streaming media with the terminal according to the content delivery channel information, thereby realizing TsTV services in an IMS system. 
     In view of the above, a TsTV service establishment method and a TsTV MF entity of the present disclosure have been illustrated above in detail. It will be apparent to those skilled in the art that various modifications and variations can be made to the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided that they fall within the scope of the following claims and their equivalents.