Abstract:
The present disclosure provides a method and an Application Server (AS) for obtaining user&#39;s capability in Third Party Call Control (3PCC), and the method comprises: when a user performs 3PCC, an AS stores the media information of the user; the AS performs media negotiation with the user according to the stored media information of the user. The application of the present disclosure solves the problem of the high failure probability of media negotiation caused by the current incorrect method for obtaining the user&#39;s media capability, and improves the utilization experience of users.

Description:
TECHNICAL FIELD 
       [0001]    The disclosure relates to the field of communications, and in particular to a method and an Application Server (AS) for obtaining user&#39;s capability in Third Party Call Control (3PCC). 
       BACKGROUND 
       [0002]    In the service flow of 3PCC, such as call forwarding on no reply and transfer, when an AS initiates a new call, an invite message (INVITE) sometimes needs to contain a media Session Description Protocol (SDP), in order to negotiate with a new called user. As shown in  FIG. 1 , a user A performs media negotiation with a user B, then an AS initiates a call to a user C, that is, the AS sends an invite message to the user C, wherein the invite message contains an SDP. 
         [0003]    The specific application scenario is as follows: 
         [0004]    1. as shown in  FIG. 2 , a flow of call forwarding on no reply comprises the following steps:
       step  201 : a user A initiates a call establishment message to a user B via an AS, that is, the user A sends an invite message to the user B through the AS, wherein the invite message contains SDP_A 1 ;   step  202 : the user B returns a 183 message which contains SDP_B 1 ;   steps  203 - 204 : the user A and the user B perform interaction of a PRACK message and a 200 OK message;   step  205 : the user A returns an update message (UPDATE) which contains SDP_A 2 ;   step  206 : the user B returns a 200 OK message which contains SDP_B 2 ;   step  207   a : the user B returns a 180 message of ringing;   step  207   b : no reply timeout of the user B triggers a call forwarding on no reply;   step  208 : the AS initiates a call to a user C, that is, the AS sends an invite message to the user C, wherein the invite message contains SDP_A 2 ; and   step  209 : the user A and the user C perform media negotiation according to SDP_A 2 .       
 
         [0014]    2. As shown in  FIG. 3 , a flow of transfer comprises the following steps:
       step  301 : a user A initiates a call establishment message to a user B via an AS, that is, the user A sends an invite message to the user B through the AS, wherein the invite message contains SDP_A 1 ;   step  302 : the user B returns a 183 message which contains SDP_B 1 ;   steps  303 - 304 : the user A and the user B perform interaction of a PRACK message and a 200 OK message;   step  305 : the user A returns an update message which contains SDP_A 2 ;   step  306 : the user B returns a 200 OK message which contains SDP_B 2 ;   step  307 : the user B returns a 180 message of ringing;   steps  308 - 309 : the user B returns a 200 OK message of pick-up and the user A returns an acknowledgement (ACK) message;   step  310 : the user A initiates a transfer request to the AS;   step  311 : the AS initiates a call establishment request to a user C, that is, the AS sends an invite message to the user C, wherein the invite message contains SDP_B 2 ; and   step  312 : the user C performs negotiation according to SDP_B 2  and returns a response SDP_C 1 .       
 
         [0025]    In the flows above, there exists a common problem, that is, the user media carried when calling the user C is probably negotiated with another user, being negotiated means that this media is probably not the initial user media; and the specific content of the media, such as encoding/decoding format, might probably be selected (that is, be reduced or changed), due to the negotiation; if this media is used for calling the user C, the failure probability of media negotiation with the user C might be increased. 
         [0026]    Flow examples with the problem are specifically as follows: 1. The flow of call forwarding on no reply: providing:
       media format supported by the user A is: 4(G723) and 18(G729);   media format supported by the user B is: 4(G723);   media format supported by the user C is: 18(G729);   accordingly, when the user A calls the user B, the user B does not reply, and the media format negotiated by the user A and the user B is 4(G723);   if the negotiated media of the user A with the media format of 4(G723) is used for is calling the user C, the negotiation fails; however, actually, the user A which supports 4(G723) or 18(G729) and the user C which supports 18(G729) could have performed negotiation successfully.       
 
         [0032]    2. The flow of transfer providing:
       media format supported by the user A is: 4(G723)   media format supported by the user B is: 4(G723) and 18(G729);   media format supported by the user C is: 18(G729);   accordingly, when the user A calls the user B, since the initial media of the user A is only provided with the media format of 4(G723) and the user B is the called party, 4(G723) is selected as the media format of negotiated media of the user B for response; since the media with media format of 4(G723) is carried as the media of the user B when calling the user C, but the user C supports 18(G729) other than 4(G723), the negotiation fails; however, actually, the user B which supports 4(G723) or 18(G729) and the user C which supports 18(G729) theoretically could have performed negotiation successfully.       
 
         [0037]    It can be seen from the examples above that, in actual application, the failure probability of media negotiation is increased due to the incorrect method for obtaining the user&#39;s media capability; therefore, a technical solution is required to solve the problem above. 
       SUMMARY 
       [0038]    The technical problem to be solved by the disclosure is to provide a method and an Application Server (AS) for obtaining user&#39;s capability in Third Party Call Control (3PCC), which solve the problem of the high failure probability of media negotiation caused by the current incorrect method for obtaining the user&#39;s media capability. 
         [0039]    In order to solve the problem above, the disclosure provides a method for obtaining user&#39;s capability in 3PCC, and the method comprises the following steps:
       when a user performs 3PCC, an AS stores media information of the user; and the AS performs media negotiation with the user according to the stored media information of the user.       
 
         [0041]    The present disclosure also provides an AS used for a user to perform 3PCC, wherein the AS is configured to store media information of the user and to perform media negotiation according to the stored media information of the user. 
         [0042]    Compared with the prior art, application of the present disclosure solves the problem of the high failure probability of media negotiation caused by the current incorrect method for obtaining the user&#39;s media capability, and improves the utilization experience of users. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0043]      FIG. 1  shows a flowchart illustrating that a user A performs media negotiation with a user B and an AS initiates a call to a user C according to the prior art; 
           [0044]      FIG. 2  shows a flowchart of call forwarding on no reply according to the prior art; 
           [0045]      FIG. 3  shows a flowchart of transfer according to the prior art; 
           [0046]      FIG. 4  shows a flowchart of call forwarding on no reply according to an embodiment of the present disclosure; and 
           [0047]      FIG. 5  shows a flowchart of transfer according to an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0048]    The present disclosure is further illustrated below in conjunction with accompanying drawings and specific embodiments. 
         [0049]    The main idea of the present disclosure is: an AS stores media information of a user; when the user performs 3PCC, the AS performs media negotiation according to the stored media information of the user. 
         [0050]    Specifically: a method, a processing policy and an applicable scenario, for obtaining a relatively full media capability by storing the original media and by switching among users using a re-invite message containing no media, which are not limited to the service of the call forwarding on no reply and the transfer service; and the present disclosure is also applicable to other third party control call services. 
         [0051]    Specifically, there is Method 1: the AS stores the media of a calling user when the calling user carries its own media for the first time, and then sends the obtained media when a call is needed to be sent; 
         [0052]    Specifically, there is Method 2: for the acquisition of the media of a called user, the AS needs to send a re-invite message containing no media to the called user after a call is made, and stores the media after a response which contains the media and made by the called user is reported, and then sends the obtained media when the media is needed to be sent. 
         [0053]    For the calling user, Method 1 is generally applied, because the calling user generally carries a set of its own media when initiating a call; of course, Method 2 also can be applied to obtaining the media. If the calling user carries no media when initiating a call, in this situation, the called user returns media first, and Method 2 is needed to obtain the media of the calling user. 
         [0054]    For the called user, Method 2 is generally applied; if the calling user carries no media when calling the called user, then the media returned by the called user for the first time can also be stored to be used when a call is initiated, similar to Method 1. 
         [0055]    The AS provided by the present disclosure is used in the process that a user performs 3PCC. 
         [0056]    The Application Server (AS) is configured to store the media information of the user and perform media negotiation according to the stored media information of the user. 
         [0057]    When the user performs service of 3PCC call forwarding on no reply, the step that the AS stores the media information of the user comprises:
       the AS interacts with the calling user to obtain and store the media information of the calling user when the calling user carries its own media information for the first time.       
 
         [0059]    When the calling user performs 3PCC transfer service, the step that the AS stores the media information of the user comprises: 
         [0060]    the AS sends a re-invite message containing no media information to the called user after the calling user makes a call with the called user, and stores the media information of the called user contained in a response returned by the called user. 
         [0061]    The present disclosure is further illustrated below in conjunction with specific embodiments. 
         [0062]    1. An AS stores the original media of a calling user into a data area, makes no change to the media in the following negotiation, and waits to carry the media when a call is sent; as shown in  FIG. 4 , the flow comprises the following steps:
       step  401 : a user A initiates a call establishment message to a user B via an AS, that is, the user A sends an INVITE message to the user B through the AS, wherein the INVITE message contains media SDP_A 1 ; the AS stores the media into the data area;   step  402 : the user B returns to the user A a 183 message which contains media SDP_B 1 ;   steps  403 - 404 : the user A and the user B perform interaction of a PRACK message and a 200 OK message;   step  405 : the user A returns to the user B an update message which contains media SDP_A 2 ;   step  406 : the user B returns to the user A a 200 OK message which contains media SDP_B 2 ;   step  407   a : the user B returns a 180 message of ringing;   step  407   b : no reply timeout of the user B ringing triggers a call forwarding on no reply;   step  408 : the AS initiates a calling message to a user C, that is, the AS sends an is INVITE message to the user C, wherein the INVITE message contains media SDP_A 1 ; and   step  409 : the user C performs media negotiation with the user A according to the received media SDP_A 1 .       
 
         [0072]    The user A performs end-to-end negotiation with the user C, and the subsequent process is performed. 
         [0073]    2. An AS obtains the media of a called user by switching using a re-invite message containing no media after making a call with the called user, and stores the obtained media after finishing the re-invite process and then waits to carry the media when a call is sent; as shown in  FIG. 4 , the flow comprises the following steps:
       step  501 : a user A initiates a call establishment message to a user B via an AS, that is, the user A sends an INVITE message to the user B through the AS, wherein the INVITE message contains media SDP_A 1 ;   step  502 : the user B returns to the user A a 183 message which contains media SDP_B 1 ;   steps  503 - 504 : the user A and the user B perform interaction of a PRACK message and a 200 OK message;   step  505 : the user A returns to the user B an update message which contains media SDP_A 2 ;   step  506 : the user B returns to the user A a 200 OK message which contains media SDP_B 2 ;   step  507 : the user B returns a 180 message of ringing;   steps  508 - 509 : the user B returns a 200 OK message of pick-up to the user A and the user A returns an ACK message to the user B;   step  510 : the user A initiates a transfer request to the AS;   step  511 : the AS sends a re-invite message containing no media to the user B, wherein the re-invite message is expressed as re-INVITE (with no SDP);   step  512 : the user B returns to the AS a 200 OK response which contains media SDP_B 3 ; and the AS stores the obtained media SDP_B 3 ;   step  513 : the AS initiates a call establishment request to the user C, that is, the AS sends an INVITE message to the user C, wherein the INVITE message contains SDP_B 3 ;   step  514 : the user C performs negotiation according to the received media SDP _B 3  and returns a temporary or final response SDP_C 1  to the AS; and   step  515 : the AS sends to the user B an ACK message which contains SDP_C 1 ; the user B and the user C performs end-to-end negotiation, and the subsequent process is performed.       
 
         [0087]    The above is only the preferred specific embodiments of the present disclosure; however, the protection scope of the present disclosure is not limited to the above; any changes and substitutes easily thought by those skilled in the art, within the technical scope of the present disclosure, shall be included within the protection scope of the present disclosure; therefore, the protection scope of the present disclosure should be based on the protection scope of the claims.