Abstract:
The present invention establishes a new protocol that supports the continuity of a single radio voice call onto a circuit switched communications system through the use of a special addressing identifier. This special identifier is called the single radio voice call identifier, and it designates the use of a single radio voice call continuity procedure for the transition to the circuit switched communication system. The applications server receives the single radio identifier and performs the transfer of the single radio voice session without the need for other address or identifier information, and also uses the single radio identifier or a new message type to initiate the correlation of parameters related to service control session establishment in later steps.

Description:
RELATED APPLICATION DATA 
       [0001]    This application is related to Provisional Patent Application Ser. No. 61/049,180 filed on Apr. 30, 2008, and priority is claimed for this earlier filing under 35 U.S.C. §119(e). The Provisional Patent Applications are incorporated by reference into this utility patent application. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    A method for supporting continuity of single radio voice call communications in a transition to a circuit switched network. 
       BACKGROUND OF THE INVENTION 
       [0003]    IP-based mobile systems provide for communication using mobile user equipment on wireless communication networks. Among other elements, the transition of connectivity from one wireless communication system to another would involve a source network and a target network in a transition of communication services. The user equipment, source network, and target network may be called different names depending on the nomenclature used and the base technology used in the particular network configurations or communication systems. 
         [0004]    For instance, the term “user equipment” includes a mobile node or mobile communication unit (e.g., mobile terminal, “smart phones”, nomadic devices such as laptop PCs with wireless connectivity, as described in greater detail below), and “user equipment” is sometimes called mobile nodes, mobile unit, mobile terminal, mobile device, or similar names depending on the nomenclature adopted by particular system providers. Direct wireless connectivity to a cellular network supports various makes and models of mobile terminals (“cell phones”) having various features and functionality, such as Internet access, e-mail, messaging services, and the like. But, generally, “user equipment” can encompass PC&#39;s having cabled (e.g., telephone line (“twisted pair”), Ethernet cable, optical cable, and so on) connectivity to the wireless network, as well as direct wireless connectivity to the cellular network. 
         [0005]    In great majority of deployed mobile networks voice calls are provided over the Circuit Switched (CS) domain. In new mobile network deployments (especially with the advent of 3G High Speed Packet Access (HSPA) and the future E-UTRAN access) it is expected that voice will be supported over the Packet Switched (PS) domain via the IP Multimedia Subsystem (IMS) specified by 3GPP. In order to support voice call continuity between the IMS and the legacy CS domain, 3GPP has initiated specification work on Voice Call Continuity (VCC) in Release-7 specification (TS° 23.206) and this was later generalized to apply to non-voice IMS sessions and was referred to as IMS Session Continuity in Release-8 (TS° 23.237). In the VCC approach for voice continuity, the voice call/session is anchored in a Back-to-Back User Agent (B2BUA) located in the IMS network and referred to as the Session Continuity Control Application Server (SCC AS). 
         [0006]    User equipment engaged in a voice call over the PS domain network (in this context the source network) establishes a so-called IMS Access Leg with the SCC AS. If the user equipment is transitioned to a circuit switched communication network (in this context the target network), the circuit switched network establishes a CS Access Leg connection with the SCC AS, which eventually leads to the SCC AS performing the transfer of the voice session on this CS Access Leg connection and releasing of the network resources associated with the IMS Access Leg connection. In order to identify the session that needs to be transferred, however, the SCC AS needs to receive an explicit session identifier. This is typically how the procedure would work in a “dual radio” context, where the CS Access Leg is established by the terminal itself, so it can provide an explicit address identifier for the session that it wishes to transfer. 
         [0007]    However, this is not possible in the “single radio” environment (under consideration here), because in single radio environment the CS Access Leg establishment is triggered from the CS domain core network (i.e. the MSC Server enhanced for single radio VCC), rather than from the user equipment. Because the prior art systems (CS domain core network) are unable to provide the explicit identifier of the session that the user wishes to transfer, a new method is needed to allow the SCC AS to identify the session that the user wishes to transfer. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention resolves the problem of identification of the session that needs to be transferred to the circuit switched system by establishing a new protocol that supports the continuity of a single radio voice call onto a circuit switched communications system through the use of a special addressing identifier. This special identifier is called the single radio voice call procedure identifier (shortly “single radio identifier” or “SRI”), and it designates the use of a single radio voice call continuity procedure for the transition to the circuit switched communication system. The SCC applications server receives the single radio identifier and performs the transfer of the active voice session without the need for other address or identifier information that would normally have been required in prior art transition protocols (e.g., “dual radio” systems). The applications server also uses the single radio identifier or a new message type to correlate the service control session establishment in later steps, which assists with the allocation of resources and improves the performance of the communications systems after the transition of services to the circuit switched communication system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The objects and features of the invention will become more readily understood from the following detailed description and appended claims when read in conjunction with the accompanying drawings in which like numerals represent like elements and in which: 
           [0010]      FIG. 1  is the architecture for single radio voice call continuity between packet-based E-UTRAN access and GERAN or UTRAN based circuit switched access as specified in 3GPP TS° 23.216; 
           [0011]      FIG. 2  is a message sequence showing the use of the single radio voice call procedure identifier in the present invention; and, 
           [0012]      FIG. 3  is a message sequence showing the use of the single radio voice call procedure identifier in the present invention and a new message type. 
       
    
    
       [0013]    The objects and features of the invention will become more readily understood from the following detailed description and appended claims when read in conjunction with the accompanying drawings in which like numerals represent like element. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]    In  FIG. 1 , the overall architecture for single radio voice call continuity between a packet-based E-UTRAN access and a GERAN or UTRAN based circuit switched access  100  showing a single radio voice call transition for user equipment  101 . Prior to transition to the circuit switched network, the user equipment  101  is coupled to other servers, user equipment and the IP Multimedia Subsystem (IMS)  137  via connection  110  through the E-UTRAN server  115  and the Serving/PDN GW gateway  135 . The IMS subsystem  137  can also communicate with the user equipment  101  via line  140 . After transition to the circuit switched network, the user equipment  101  is coupled to other servers, user equipment, or the IMS  137  through the Target UTRAN/GERAN server  190  and the MSC Server  192 . The IMS network  137  possesses the Session Continuity Control (SCC) Application Server (not shown) used in the transition of the user equipment  101  voice call from the source network to the target network. 
         [0015]    Specifically, on the source network, the user equipment  101  is coupled to the E-UTRAN server  115  via connection  120 , and the E-UTRAN server  115  is coupled to the Serving/PDN GW  135  via connection  125 . And, the Serving/PDN GW  135  is coupled to the IMS network  137  through connection  138 . The E-UTRAN is coupled to the MME server  170  through the S1-MME connection  147 , and the Serving/PDN GW  135  is coupled to the MME server  170  through the S 11  connection  145 . 
         [0016]    The MME server  170  is coupled to the Home Serving Server  155  through the SGa connection  160 . The MME server  170  is coupled to the MSC Server  192  via the Sv connection  175 , and the MME Server  170  is coupled to the SGSN server  182 , which is coupled to the Target UTRAN/GERAN server  190  via the S3 connection  180  and the Iu-ps/GS connection  185 , respectively. 
         [0017]    On the target network, the user equipment  101  is coupled to the target UTRAN/GERAN server  190  via the Um/Uu connection  168 , and the target UTRAN/GERAN server is coupled to the MSC Server  192  via the Iu-cs/A connection  167 . The MSC Server  192  is coupled to the IMS network  137  via connection  152 . 
         [0018]    The invention covers the protocol of transitioning the user equipment  101  from the connectivity to the E-UTRAN server  115  and Serving/PDN GW gateway  135  on the source network to the Target UTRAN/GERAN  190  and MSC Server  192  on the target network. The target network would normally acquire specific address and identifier information for the user equipment prior to transition from the serving entities and servers on the source network, but the prior art protocols (e.g. dual radio) operated on the source network do not normally permit the serving entities to process or possess this type of specific address and identifier information. Further, it is important for the transition to be designated as a single radio voice call for proper handling of the transition and the allocation and conservation of network resources. The present invention provides a single radio voice call identifier SRI that provides alternative information to satisfy the need for the circuit switched target network to acquire the address and identifier information. 
         [0019]    In the present invention referring to  FIG. 2 , the circuit switched(CS)/IMS intermediate nodes  220  transmit an INVITE message  230  to the Intermediate Servers (I-S/CSCF) servers  225  where the INVITE message includes a single radio voice call identifier SRI as well as a session description protocol information/media description (SDP-MGW) parameters. The session description protocol information/media description (SDP-MGW) parameters in message  230  include IP addresses, port numbers, and other description information for the user equipment connections to the network. 
         [0020]    The Intermediate Servers (I-S/CSCF) servers  225  transmit an INVITE message  232  to the session continuity control application server SCC/AS  247  on the IMS subsystem network  137 . The INVITE message  232  also includes a single radio voice call identifier SRI as well as a session description protocol information/media description (SDP-MGW) parameters. The session continuity control application server  247  on the IMS network  137  will use the single radio voice call identifier SRI to determine that a transfer of the user equipment single radio voice call has been requested. Upon receipt, the SCC/AS application server  247  will perform the transfer of the active voice session for the single radio voice call by updating the access leg connections with the appropriate information for the target circuit switched connections in step  240 , which includes the media description and other information needed to support the transition of the single radio voice call on the circuit switched target network. 
         [0021]    If the user equipment is capable of establishing a Packet Switched (PS) connection in parallel to the circuit switched (CS) domain voice call (e.g. if the access network is UTRAN), an INVITE transmission  245  is subsequently sent from the user equipment  101  to the Intermediate Servers (I-S/CSCF) servers  225  where the INVITE message includes a single radio voice call identifier SRI as well as a session description protocol information/circuit switch (SDP-cs) parameters. The session description protocol information/circuit switch (SDP-cs) parameters in message  245  include IP addresses, port numbers, and other description information for the user equipment connections to the circuit switched target network. 
         [0022]    The Intermediate Servers (I-S/CSCF)  225  transmit an INVITE message  248  to the session continuity control application server SCC/AS  247  on the IMS network  137 . The INVITE message  248  also includes a single radio voice call identifier SRI as well as a session description protocol information/circuit switch (SDP-cs) parameters. In step  250 , the session continuity control application server SCC/AS  247  on the IMS network  137  will use the single radio voice call indicator SRI to correlate the access transfer request with the access transfer request received for the active session previously received in INVITE message  232 . In step  255 , the SCC/AS  247  will also release the resources associated with the source network access leg. 
         [0023]    In the present invention referring to  FIG. 3 , the circuit switched(CS)/IMS intermediate nodes  320  transmit an INVITE message  330  to the Intermediate Servers (I-S/CSCF) servers  325  where the INVITE message includes a single radio voice call identifier SRI as well as a session description protocol information/media description (SDP-MGW) parameters. The session description protocol information/media description (SDP-MGW) parameters in message  330  include IP addresses, port numbers, and other description information for the user equipment connections to the network. 
         [0024]    The Intermediate Servers (I-S/CSCF) servers  325  transmit an INVITE message  332  to the session continuity control application server SCC/AS  347  on the IMS network  137 . The INVITE message  332  also includes a single radio voice call identifier SRI as well as a session description protocol information/media description (SDP-MGW) parameters. The session continuity control application server  347  on the IMS network  137  will use the single radio voice call identifier SRI to determine that a transfer of the user equipment single radio voice call has been requested. Upon receipt, the SCC application server  347  will perform the transfer of the active session for the single radio voice call by updating the access leg connections with the appropriate information for the target circuit switched connections in step  340 , which includes the media description and other information needed to support the transition of the single radio voice call on the circuit switched target network. 
         [0025]    Subsequently, a RE-INVITE transmission message  345  is sent from the user equipment  101  to the Intermediate Servers (I-S/CSCF) servers  325  where the RE-INVITE message, by its message format, indicates to the servers that it is related to an existing SIP dialog. The Intermediate Servers (I-S/CSCF)  325  transmit a RE-INVITE message in step  348  to the session continuity control application server SCC/AS  347  on the IMS network  137 . In step  350 , the session continuity control application server  347  on the IMS network  137  will use the RE-INVITE message and associated information therein to correlate the access transfer request with the access transfer request received for the voice session previously received in INVITE message  332 . In step  355 , the SCC/AS  347  will also release the resources associated with the source network access leg. 
         [0026]    Modifications of the present invention allow for the transition of the single radio voice call to a circuit switched network to be modified to accommodate different identifiers as long as security associations are valid and other necessary requirements are maintained. While preferred embodiments of the invention have been shown and described, modifications thereof can be made by one skilled in the art without departing from the spirit and teachings of the invention. For example, the same solution also applies to the architecture for single radio voice call continuity from IMS over 3G UTRAN/HSPA access to GERAN/UTRAN CS domain access. The embodiments described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention. 
         [0027]    Having described the invention, we claim: