Abstract:
Method and apparatus, including computer program products, are provided for SRVCC emergency call support. The method may include receiving, at a mobility switching center, a first message representing a request to handover an emergency communication session from a first network to a second network. The mobile switching center may obtain a value representing an emergency session transfer number. The mobility switching center may also send a second message to the first network. The second message may initiate handover of the emergency communication session from the first network to the second network. The second message may comprise the value representing the emergency session transfer number. Related apparatus, systems, methods, and articles are Receive Session Continuity Data also described.

Description:
FIELD 
       [0001]    The present invention relates generally to communication networks. More specifically, the present invention relates to communication networks supporting emergency sessions and calls. 
       BACKGROUND 
       [0002]    Currently developed telecommunication technologies provide solutions for performing a handover (HO) operation from a Long Term Evolution (LTE) or High Speed Packet Access (HSPA) system to a second generation (2G) or third generation (3G) cellular telecommunications network under non-emergency conditions. Such an operation often involves a handover from a Voice over Internet Protocol (VoIP) session using Internet Protocol Multimedia Subsystems (IMS) to a circuit switched domain, and is sometimes referred to as a single radio voice call continuity (SRVCC) operation. 
         [0003]    In currently available SRVCC operations, a handover typically involves a mobile switching center (MSC) executing a domain transfer using a session transfer number (STN-SR). The STN-SR may be a unique number or value (such as an E.164 address) that is stored in a Home Subscriber Server (HSS) of a user. The STN-SR routes to a Service Centralization and Continuity Application Server (SCC AS) of the home network. In some implementations, the home network represents a network which includes a home subscriber server for the user equipment. Although telecommunication technologies provide for such handover operations under normal conditions, currently available technologies fail to provide adequate solutions for such a handover during an emergency session. 
         [0004]    This deficiency is due, at least in part, to the fact that the STN-SR routes to an SCC AS in the user&#39;s home network, whereas emergency calls or sessions are assumed to be in a visiting network. Additionally, Dual-Radio Voice Call Continuity (Dual-Radio VCC) technology fails to provide a viable solution. In Dual-Radio VCC, the SCC AS returns a dynamic STN to the UE in session initiation protocol (SIP) signaling when the emergency call is established. The UE then uses the dynamic STN to execute a domain transfer. However, this solution cannot be used in an emergency SRVCC scenario because an SRVCC handover and domain transfer is triggered by the visited network, which is not aware of the dynamic STN. Accordingly, currently available telecommunication technologies fail to provide support for SRVCC emergency calls or sessions. 
       SUMMARY 
       [0005]    A method and apparatus, including computer program products, are provided for SRVCC emergency call support. 
         [0006]    In one aspect there is provided a method. The method may include receiving, at a mobility switching center, a first message representing a request to handover an emergency communication session from a first network to a second network. The mobile switching center may obtain a value representing an emergency session transfer number. The mobility switching center may also send a second message to the first network. The second message may initiate handover of the emergency communication session from the first network to the second network. The second message may comprise the value representing the emergency session transfer number. 
         [0007]    In another aspect there is provided an apparatus. The apparatus may include at least one processor and at least one memory. The at least one processor and the at least one memory may be configured to provide operations. The operations may comprise receiving a first message representing a request to handover an emergency communication session from a first network to a second network. The operations may further comprise obtaining a value representing an emergency session transfer number. The operations may further comprise sending a second message to the first network. The second message may initiate handover of the emergency communication session from the first network to the second network. The second message may comprise the value representing the emergency session transfer number. 
         [0008]    In yet another aspect a computer-readable medium may include code which when executed on at least one processor provides a process. The process may comprise receiving a first message representing a request to handover an emergency communication session from a first network to a second network. The process may further comprise obtaining a value representing an emergency session transfer number. The process may further comprise sending a second message to the first network. The second message may initiate handover of the emergency communication session from the first network to the second network. The second message may comprise the value representing the emergency session transfer number. 
         [0009]    The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims. 
     
    
     
       DESCRIPTION OF DRAWINGS 
         [0010]    In the drawings, 
           [0011]      FIG. 1  depicts a block diagram of an SRVCC emergency call support system in accordance with embodiments of the present invention; 
           [0012]      FIG. 2  depicts a block diagram of a mobility management entity (MME) in accordance with embodiments of the present invention; 
           [0013]      FIG. 3  depicts a block diagram of an SRVCC mobility switching center in accordance with embodiments of the present invention; 
           [0014]      FIG. 4  depicts a flow chart of a method for a mobility management entity to initiate an emergency session continuity procedure in accordance with embodiments of the present invention; 
           [0015]      FIG. 5  depicts a flow chart of a method for a mobility switching center to initiate an emergency session continuity procedure in accordance with embodiments of the present invention; 
           [0016]      FIG. 6  depicts a sequence flow chart of a bearer-level process for initiating an emergency session continuity procedure in accordance with embodiments of the present invention; and 
           [0017]      FIG. 7  depicts a sequence flow chart diagram of an IMS-level process for initiating an emergency session continuity procedure in accordance with embodiments of the present invention. 
           [0018]    Like labels are used to refer to same or similar items in the drawings. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  is a block diagram of an SRVCC emergency call support system  100 . The system  100  includes an Evolved Universal Terrestrial Radio Access Network (E-UTRAN)  110 , a Mobility Management Entity (MME)  120  (which may also be configured as a GPRS Support Node (SGSN)), an SRVCC Mobile Switching Center (SRVCC MSC)  130 , a 3rd Generation Partnership Program (3GPP) Internet Protocol Multimedia Subsystem (IMS)  140 , a 3rd Generation Access Network (3G)  150 , and a user device  160 . The components of the system  100  cooperate to enable support for a Single Radio Voice Call Continuity (SRVCC) emergency call in accordance with the implementations described herein. 
         [0020]    In certain embodiments, the user device  160  initiates an IMS emergency session with a Long Term Evolution (LTE) or High Speed Packet Access (HSPA) network, represented by the E-UTRAN  110 . In some embodiments, the E-UTRAN  110  is a visited network with respect to the user device  160 . The emergency session may be a Voice over Internet Protocol (VoIP) IMS session. In some embodiments, as the user device  160  moves, E-UTRAN  110  is configured to detect that a handover (HO) of the session to the 2G/3G Access Network  150  may be desirable because the radio access area for the VoIP/IMS session has become weak. 
         [0021]    In such a scenario, the E-UTRAN  110  may initiate an SRVCC operation, which may include performing or executing operations found in Release 8 of Technical Specification (TS) 23.216 of the 3rd Generation Partnership Program (3GPP). In some embodiments, this may include the E-UTRAN  110  communicating with the MME  120  to indicate a need to perform a single radio voice call continuity (SRVCC) operation for the emergency session established by the user device  160 . 
         [0022]    In response, the MME (or SGSN)  120  may use a “Sv” interface to initiate the SRVCC operation. In some embodiments, the MME  120  may provide the MSC  130  with an Emergency Session Transfer Number for SRVCC (E-STN-SR) to facilitate the SRVCC operation. In other embodiments, the MME may indicate a need to perform an SRVCC operation for the emergency session without providing an E-STN-SR. 
         [0023]    In certain embodiments, the MSC  130  may be configured to obtain the E-STN-SR from the MME  120 . In some embodiments, the MSC  130  may be configured to obtain the E-STN-SR by generating the E-STN-SR or by retrieving the E-STN-SR from a local data repository. In certain embodiments, the E-STN-SR is a non-unique number or value which may not be stored in a Home Subscriber Server, as opposed to the STN-SR value or number that is often stored in a Home Subscriber Server for each user and used in an SRVCC operation under normal or non-emergency scenarios. The E-STN-SR may be configured to point to a local IMS network that handles the IMS emergency session. 
         [0024]    Upon obtaining the E-STN-SR, the MSC  130  (or MSC enhanced with SRVCC) may use the E-STN-SR to initiate an SRVCC operation or “session continuity” operation by communicating with the 3GPP IMS  140  as defined in 3GPP TS 23.216. As a result, when the local IMS receives the INVITE with E-STN-SR, the local IMS may perform a domain transfer using a Domain Transfer Function  142  (DTF or SCC AS) and an Emergency Call Session Control Function (E-CSCF)  144 , which may include procedures similar to those defined in 3GPP TR 23.826 (section 6.1.4.2) for Dual Radio VCC. Additionally, the MSC  130  may initiate a handover procedure with the target network as defined in 3GPP TS 23.216. 
         [0025]    Additional procedures may also be performed by the system  100  to complete the SRVCC operation. Such procedures may include those defined by 3GPP TS 23.216, where a handover (HO) command (CMD) is sent to the user device  160  and the user device  160  switches over to the 2G/3G Access Network  150 . Accordingly, the system  100  provides a solution for supporting SRVCC emergency calls by using an E-STN-SR that is locally generated or stored in the visited network. 
         [0026]    It should be appreciated that a system, in accordance with the present invention, may include terminals, nodes and networks in addition to the components depicted in the system  100  of  FIG. 1 . Additionally, a visited IMS network may be used for routing a session to a Public Safety Answering Point (PASP), and a Session Initiation Protocol (SIP) may be anchored by a Domain Transfer Function (DTF) server or a Centralization and Continuity Application Server (SCC AS) similar to those presented in 3GPP TR 23.826. 
         [0027]      FIG. 2  is a block diagram of a mobility management entity (MME)  200 . The MME  200  includes a network interface  210 , a processor  220 , a user interface  230 , a volatile memory  240 , and a nonvolatile memory  250 . In certain embodiments, the MME  200  of  FIG. 2  corresponds to the MME  120  of  FIG. 1 . In some embodiments, the MME  120  may be a Serving GPRS Support Node (SGSN) as depicted in  FIG. 1  and  FIG. 6 . The components of the MME  200  cooperate to initiate an emergency session continuity. 
         [0028]    In certain embodiments, the network interface  210  is configured to enable communication between the MME  200  and other network devices. In some embodiments, such network devices may include those represented by  FIG. 1 , such as a device of the E-UTRAN  110  or the MSC  130 . The network interface  210  may include one or more hardware components operating in accordance with one or more protocols or software instructions. Accordingly, the network interface  210  may enable communication between the MSC  300  and one or more network devices to facilitate the initiation of an emergency session continuity procedure. 
         [0029]    In some embodiments, the processor  220  may be configured to receive session continuity data from a radio access network, such as an E-UTRAN or a UTRAN. The session continuity data may include an indication of an emergency SRVCC event or operation. An emergency SRVCC event may include a scenario where a handover of an emergency call is required because a mobile device has initiated an IMS emergency session with a visiting LTE or HSPA device, but a handover of the emergency session is required. Accordingly, the processor  220  may be configured to receive session continuity data from a radio access network to facilitate supporting an SRVCC emergency call. 
         [0030]    In some embodiments, the processor  220  may also be configured to initiate an emergency session continuity procedure via an MSC. In some embodiments, the MSC may correspond to the MSC  130  of  FIG. 1  or the MSC  300  of  FIG. 3 . In some embodiments, the processor  220  may be configured to initiate an emergency session continuity procedure by communicating emergency session continuity data to the MME. The emergency session continuity data may include an Emergency Session Transfer Number for SRVCC (E-STN-SR). In some embodiments, the E-STN-SR is configured to point toward a local IMS network that handles the emergency session. In other embodiments, the emergency session continuity data may include instructions or an indication that the MSC must obtain an E-STN-SR from, for example, a local data repository. Accordingly, the processor  220  may receive session continuity data from a radio access network and initiate an emergency session continuity procedure via an MCS to facilitate the initiation of an emergency session continuity procedure. 
         [0031]    In certain embodiments, the user interface  230  may include a combination of hardware and software that facilitates communication between the mobility management entity  200  and a user of the mobility management entity  200 . For example, a user interface  230  may include one or more speakers, one or more user-pressable buttons, one or more key pads, one or more digital screens, one or more lights, or any other feature that would facilitate bidirectional communication between the mobility switching center  300  and a user. Accordingly, the user interface  230  may facilitate an interaction between a user and the mobility management entity  200 . 
         [0032]    In some embodiments, the volatile memory  240  may include any variety of volatile storage mediums. For example, the volatile memory device  240  may include a device comprising a volatile storage component, a primary storage component, a random access memory (RAM) component, and/or a dynamic random access memory (DRAM) component such as a double data rate synchronous dynamic access memory (DDR SDRAM) component. Accordingly, the volatile memory  240  may provide a temporary data storage structure that functionally interacts with other components, such as the processor  220  and the nonvolatile storage device  250 . 
         [0033]    In some embodiments, the nonvolatile memory device  250  may include a variety of nonvolatile storage mediums such as digital devices that retain data when a power supply is disconnected. For example, the nonvolatile memory device  250  may include any variety of a read-only memory (ROM) components such as a programmable read-only memory (PROM), a field programmable read-only memory (EAROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM). 
         [0034]    Examples of the nonvolatile memory device  250  may also include optical memory components such as an optical disk, a paper tape, or a punch card. Accordingly, in certain embodiments, the nonvolatile memory device  250  may be configured to functionally interact with other MSC components, such as the processor  220 , to enable and/or initiate an emergency session continuity procedure. 
         [0035]      FIG. 3  is a block diagram of an SRVCC mobility switching center (MSC)  300 . The depicted MSC  300  may include a network interface  310 , a processor  320 , a user interface  330 , a volatile memory  340 , and a nonvolatile memory  350 . In some embodiments, the MSC  300  may correspond to the MSC  130  of  FIG. 1 . The components of the MSC  300  may cooperate to initiate an emergency session continuity procedure as described herein. 
         [0036]    In some embodiments, the network interface  310  is configured to enable communication between the MSC  300  and other network devices. In some embodiments, such network devices may include those represented by  FIG. 1 , such as an MME/SGSN  120 , a 2G/3G Access Network device  150 , or a 3GPP IMS device  140 . The network interface  310  may include one or more hardware components operating in accordance with one or more protocols or software instructions. Accordingly, the network interface  310  may enable communication between the MSC  300  and one or more network devices to facilitate the initiation of an emergency session continuity procedure. 
         [0037]    In some embodiments, the processor  320  is configured to receive continuity data corresponding to a handover operation of an emergency session. The continuity data may include an indication of an emergency SRVCC operation or event. An emergency SRVCC event may include a scenario where a handover of an emergency call is required because a mobile device has initiated an IMS emergency session with a visiting LTE or HSPA device, but a handover of the emergency call is required. In some embodiments, the emergency session continuity data is received from an MME. As mentioned above, the emergency session continuity data may include an Emergency Session Transfer Number for SRVCC (E-STN-SR). In some embodiments, the E-STN-SR is configured to point toward a local IMS network (e.g. an IMS network which a user is visiting) that handles the emergency session. Additionally, the E-STN-SR may be a non-unique number. Accordingly, the processor  320  may be configured to receive continuity data corresponding to an emergency session. 
         [0038]    In some embodiments, the processor  320  may be also configured to obtain emergency session transfer data in response to receiving the session continuity data. In certain embodiments, the processor  320  is configured to obtain the session transfer data from a local data repository such as the nonvolatile memory  350 . In some embodiments, the processor  320  is configured to obtain the session transfer data from the emergency session transfer data received. As noted above, the session transfer data may include data received from an MME such as the MME  130  of  FIG. 1 . Accordingly, the processor  320  may be configured to obtain emergency session transfer data in response to receiving the session continuity data. 
         [0039]    In some embodiments, the processor  320  may be configured to initiate an emergency session continuity procedure using the emergency session transfer data. As noted above, the emergency session continuity data may be a non-unique number. In certain embodiments, the emergency session continuity procedure comprises an emergency session continuity procedure with a local visited IMS network. In some embodiment, the emergency session continuity procedure follows a set of operations as those set forth in 3GPP TR 23.826, where a domain transfer function (DTF or SCC AS) performs a switching of access legs from IMS to circuit switched (CS). In some embodiments, emergency session continuity procedure also includes performing a handover procedure with a target access as defined by 3GPP TR 23.8216. Accordingly, the processor  320  may be configured to initiate an emergency session continuity procedure using the emergency session transfer data. 
         [0040]    In some embodiments, the user interface  330  may include a combination of hardware and software that facilitates communication between the mobility switching center  300  and a user of the mobility switching center  300 . For example, a user interface  330  may include one or more speakers, one or more user-pressable buttons, one or more key pads, one or more digital screens, one or more lights, or any other feature that would facilitate bidirectional communication between the mobility switching center  300  and a user. Accordingly, the user interface  330  may facilitate an interaction between a user and the mobile switching center  300 . 
         [0041]    In some embodiments, the volatile memory  340  may include any variety of volatile storage mediums. For example, the volatile memory device  340  may include a device comprising a volatile storage component, a primary storage component, a random access memory (RAM) component, and/or a dynamic random access memory (DRAM) component such as a double data rate synchronous dynamic access memory (DDR SDRAM) component. Accordingly, the volatile memory  340  may provide a temporary data storage structure that functionally interacts with other components, such as the processor  320  and the nonvolatile storage device  350 . 
         [0042]    In some embodiments, the nonvolatile memory device  350  may include a variety of nonvolatile storage mediums such as digital devices that retain data when a power supply is disconnected. For example, the nonvolatile memory device  350  may include any variety of a read-only memory (ROM) components such as a programmable read-only memory (PROM), a field programmable read-only memory (EAROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM). Examples of the nonvolatile memory device  350  may also include optical memory components such as an optical disk. Accordingly, in some embodiments, the nonvolatile memory device  350  may be configured to functionally interact with other MSC components, such as the processor  320 , to enable and/or initiate an emergency session continuity procedure. 
         [0043]    The processor, such as processor  220  or  320  may be implemented as a hardware circuit comprising custom VLSI circuits or gate arrays, off-the-shelf semiconductors such as logic chips, transistors, or other discrete components. The processor  320  may also be implemented in programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like. The processor  320  may also be implemented as a single processing device or as several processing devices configured to perform a given operation or task. 
         [0044]      FIG. 4  is a flow chart diagram of a method  400  for a mobility management entity to initiate an emergency session continuity procedure. The depicted method  400  includes receiving  410  session continuity data and initiating  420  emergency session continuity procedure. In some embodiments, the method  400  may be performed by the MME/SGSN  120  of  FIG. 1  or the MME  200  of  FIG. 2 . It should be appreciated that each operation of the method  400  may be performed, at least, in part by a processor of an MME, such as the processor  220  of MME  200 . The operations of the method  400  provide a solution for initiating an emergency session continuity procedure in accordance with the present invention. 
         [0045]    In some embodiments, receiving  410  may include an MME receiving continuity data from an E-UTRAN or UTRAN. The continuity data may include an indication of an SRVCC event. As noted above, an emergency SRVCC event may include a scenario where a handover of an emergency call is required because a mobile device has initiated an IMS emergency session with a visiting LTE or HSPA device. 
         [0046]    In some embodiments, initiating  420  an emergency session continuity procedure may include an MME initiating an emergency session procedure by transmitting continuity data to an MSC such as the MSC  130  of  FIG. 1 . In some embodiments, the continuity data may include an indication that an SRVCC event is required. Additionally, the continuity data may include an indication that the MSC should obtain emergency session transfer data that is stored locally on the MSC. In other embodiments, the continuity data may include emergency transfer data. Emergency session transfer data may include various data such as a unique number. Accordingly, the method  400  provides a solution for an MME to initiate an emergency session continuity procedure. 
         [0047]      FIG. 5  is a flow chart diagram of a method  500  for a mobility switching center to initiate an emergency session continuity procedure. The method  500  includes receiving  510  session continuity data, obtaining  520  emergency session transfer data, and initiating  530  emergency session continuity procedure. In some embodiments, the operations of the method  500  may be performed or executed by the MSC  130  of  FIG. 1  and/or the MSC  300  of  FIG. 3 . It should be appreciated that each of the operations for the method  500  may be performed, at least in part, by a processor of an MSC, such as the MSC  300  of  FIG. 3 . The operations of the method  500  provide one solution for initiating an emergency session continuity in accordance with the present invention. 
         [0048]    In some embodiments, receiving  510  session continuity data may include an MSC receiving an SRVCC indication from an MME such as the MME/SGSN  120  of  FIG. 1  and/or the MME  200  of  FIG. 2 . In some embodiments, the session continuity data may include an indication that the MSC should retrieve a non-unique number such as an E-STR-SN from a local data storage repository. 
         [0049]    In some embodiments, obtaining  520  emergency session transfer data may include an MSC retrieving session continuity data from a local data storage repository such as a non-volatile memory. In other embodiments, obtaining  520  emergency session transfer data may include obtaining session transfer data from the session continuity data previously received  510 . In some embodiments, the obtaining  520  may include performing one or more operations to generate emergency session transfer data. The emergency session transfer data may include a non-unique number. 
         [0050]    Initiating  530  an emergency session continuity may include an MSC using the emergency session transfer data to initiate one or more operations where a domain transfer function (DTF or SCC AS) performs a switching of access legs from IMS to CS. In some embodiments, initiating  530  may include executing or performing one or more operations corresponding to 3GPP TS 23.826. Accordingly, the method  500  provides a solution for initiating an emergency session continuity. 
         [0051]      FIG. 6  is a sequence flow chart diagram of a bearer-level process  600  for initiating an emergency session continuity procedure. The depicted process  600  includes operations performed by a user equipment (UE)  605 , an E-UTRAN/UTRAN or HSPA  610 , an MME/SGSN  615 , a MSC Server  620 , a Target UTRAN/GERAN  625 , and a 3GPP IMS  630 . In some embodiments, at least some of the operations of the bearer-level process  600  are performed by one or more of the components of the system  100 . The process  600  may initiate an emergency session continuity procedure. 
         [0052]    The process begins by the UE  605  initiating  635  an IMS emergency session and the MME/SGSN  615  indicating to a base station or to an enhanced base station that a core network and/or the UE  605  is SRVCC capable. After or during the operation  635 , reports relevant to the IMS emergency session are measured  640 . Next, the E-UTRAN  610  determines  645  that a handover to a 2G/3G network is required and communicates this to the MME  615 , as defined by TS 23.216. 
         [0053]    Upon determining  645  that a handover is required, the process  600  continues by the MME  615  initiating  650  an SRVCC for the IMS emergency session via an “Sv” interface. If a packet switched to packet switched (PS-PS) handover (HO) is needed, the MME  615  may handle the PS-PS HO  655 . Additionally, the process  600  may continue to execute  660  circuit switched handover preparations. 
         [0054]    With the operation  660 , the process  600  continues by the MSC  620  initiating  665  an IMS service continuity procedure using an E-STN-SR (emergency session transfer number single radio voice call continuity) with the target UTRAN/GERAN  625  and 3GPP IMS  630 . The process  600  continues by the MSC  620  transmitting  670  a CS HO response to the MME  615 . In turn, the MME  615  communicates  675 , to the E-UTRAN  610 , a PS HO response to coordinate an SRVCC event. A HO command is then communicated  680  to the UE  605 , and the UE  602  executes  685  the HO. Accordingly, the process  600  provides a solution for initiating an emergency session continuity procedure. 
         [0055]      FIG. 7  is a sequence flow chart diagram of an IMS-level process  700  for initiating an emergency session continuity procedure. The depicted process  700  includes a UE  705 , CS/IMS intermediate nodes  710 , an Interrogating or Service CSCF  715 , a Proxy or Emergency CSCF  720 , and a DTF/SCC AS  725 . In some embodiments, operations of the IMS-level process  700  may be performed by the system  1  of  FIG. 1 . The IMS-level process  700  provides a solution for initiating an emergency session continuity. 
         [0056]    The process  700  begins by the user equipment  705  communicating  730  an INVITE message to the P/E-CSCF  720 . Thereafter, the process  700  continues by the P/E-CSCF  720  communicating  735  an INVITE to the DTF/SCC AS  725 . Next, the DTF/SCC AS  725  operates to anchor  740  emergency session and then communicate  745  a PSAP INVITE to the P/E-CSCF  720 . The DTF/SCC AS  725  may anchor the emergency call session and act as a Back-to-back User Agent (B2BUA) as defined in 3GPP TR 23.826. 
         [0057]    After the communicating  745  of the INVITE, the CS/IMS Intermediate nodes  710  communicate  750  an INVITE message with an E-STN-SR to the I/S-CSCF  715 , and the VS-CSCF  715  communicates  755  an INVITE using the E-STN-SR to the DTF/SCC AS  725 . Then, the DTF/SCC AS  725  performs  760  a remote leg update. It should be noted that the DTF/SCC AS  725  may use the E-STN-SR to determine that Access Transfer using SRVCC is requested. The DTF/SCC AS  725  may proceed with the Access Transfer of the active session with bi-directional speech for the UE by updating the Remote Leg with the media description and other information using the Remote Leg Update procedure as specified in Clause 6.3.1.5 of G3PP TS 23.237. 
         [0058]    After the remote let update, the UE  705  communicates  765  a Re-INVITE to the I/S-CSCF  715 , and the I/S-CSCF  715  communicates  770  a Re-INVITE message to the DTF/SCC AS  725 . Upon receiving the Re-INVITE message, the DTF/SCC AS  725  performs  775  a remote leg update and also performs  780  a source access leg release. In this manner, the process  700  provides a solution for performing an emergency session continuity event in accordance with the present invention. 
         [0059]    It should be appreciated that operation  765  to  780  may be performed in accordance with procedures defined in Clauses 6.3.2.1.4 and 6.3.1.6 of 3GPP 23.237. For example, if a Gm reference point is retained upon a PS handover, then the UE sends a Re-INVITE via the PS access to update the remaining non-voice media associated with the recently added active session. Additionally, standard procedures may be used at the S-CSCF for routing of the INVITE to the SCC AS, and the SCC AS processes the Re-INVITE and updates the Remote Leg if needed. However, if the Gm reference point is not retained upon a PS handover procedure, or if there was no other non-voice media in the IMS session than the voice that was transferred to the target access, then the Source Access Leg is released. 
         [0060]    The processes described herein may be practiced in a different order, and/or with hardware elements in configurations that are different from those which are disclosed. Moreover, the subject matter described herein may be may be modified, varied, and otherwise changed while remaining within the scope of the appended claims. 
         [0061]    It should be noted that reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized are present in any single implementation. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment may be present in some implementations. One skilled in the relevant art will recognize that the invention can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in some embodiments that may not be present in all embodiments of the invention. 
         [0062]    In one aspect, a method comprises receiving session continuity data corresponding to an emergency session, obtaining emergency session transfer data, and initiating an emergency session continuity procedure using the emergency session transfer data. In some embodiments, the operations of the method are performed by an mobile switching center. In some embodiments, the receiving of the emergency session continuity data comprises receiving emergency session continuity data from a mobility management entity. In some embodiments, the receiving of the emergency session continuity data comprises receiving single radio voice call continuity data. 
         [0063]    Additionally, the obtaining of the emergency session transfer data may include obtaining emergency session transfer data from a mobility management entity. In some embodiments, the obtaining of the emergency session transfer data comprises obtaining emergency session transfer data in a local data storage repository. In some embodiments, the obtaining of the emergency session transfer data comprises obtaining a non-unique number. Furthermore, the initiating of the emergency session continuity procedure may comprise initiating an emergency session continuity procedure corresponding to an internet protocol multimedia subsystem. 
         [0064]    In another aspect, an apparatus comprises a processor configured receiving session continuity data corresponding to an emergency session, obtain emergency session transfer data, and initiate an emergency session continuity procedure using the emergency session transfer data. In some embodiments, the apparatus comprises a mobile switching center. In some embodiments, the processor may be configured to receive the emergency session continuity data from a mobility management entity. In some embodiments, the processor may be configured to receive single radio voice call continuity data. 
         [0065]    Additionally, the processor may be configured to obtain the emergency session transfer data from a mobility management entity. In some embodiments, the processor may be configured to obtain the emergency session transfer data from a local data storage repository. Furthermore, the processor may be configured to obtain the emergency session transfer data by obtaining a non-unique number. In some embodiments, the processor may be configured to initiate an emergency session continuity procedure corresponding to an internet protocol multimedia subsystem. 
         [0066]    In another aspect, a computer program is embodied on a computer-readable medium. The computer program may be configured to control a processor to perform operations that comprise receiving session continuity data corresponding to an emergency session, obtaining emergency session transfer data, and initiating an emergency session continuity procedure using the emergency session transfer data. 
         [0067]    In yet another aspect there is provided an apparatus comprises a receiving means for receiving session continuity data corresponding to an emergency session, a obtaining means for obtaining emergency session transfer data, and an initiating means for initiating an emergency session continuity procedure using the emergency session transfer data. 
         [0068]    In still another aspect, a method comprises receiving session continuity data from a radio access network, the session continuity data corresponding to an emergency session, and initiating an emergency session continuity procedure via a mobile switching center server. In some embodiments, the operations of the method are performed by a mobility management entity. In some embodiments, the initiating of the emergency session continuity procedure comprises transmitting emergency session transfer data to the mobile switching center server. 
         [0069]    In another aspect, an apparatus comprises a processor configured to receive session continuity data from a radio access network, where the session continuity data corresponds to an emergency session, and to initiate an emergency session continuity procedure via a mobile switching center server. In some embodiments, the apparatus comprises a mobility management entity. In some embodiments, the processor is further configured to transmit emergency session transfer data to the mobile switching center server. 
         [0070]    In another aspect, a computer program is embodied on a computer-readable medium. The computer program may be configured to control a processor to perform operations that comprise receiving session continuity data from a radio access network, where the session continuity data corresponds to an emergency session, and initiating an emergency session continuity procedure via a mobile switching center server. 
         [0071]    In another aspect, an apparatus comprises a receiving means for receiving session continuity data from a radio access network, where the session continuity data corresponding to an emergency session, and an initiating means for initiating an emergency session continuity procedure via a mobile switching center server. 
         [0072]    In yet another aspect, a system comprises a mobility management device and a mobility switching center. The mobility management device may be configured to receive session continuity data from a radio access network, and initiate an emergency session continuity procedure via a mobile switching center server, the session continuity data corresponding to an emergency session. The mobility switching center may be configured to receive the session continuity data, obtain emergency session transfer data, and initiate an emergency session continuity procedure using the emergency session transfer data. 
         [0073]    Articles are also described that comprise a tangibly embodied machine-readable medium (also referred to as a computer-readable medium) embodying instructions that, when performed, cause one or more machines (e.g., computers, etc.) to result in operations described herein. Similarly, computer systems, nodes of a network, and the like are also described that may include one or more processors and/or one or more memory coupled to the processor. The memory may include one or more programs that cause the processor to perform one or more of the operations described herein. 
         [0074]    The features, structures, or characteristics of the invention described throughout this specification may be combined in any suitable manner in one or more embodiments. For example, reference throughout this specification to “certain embodiments,” “some embodiments,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present invention. Thus, appearances of the phrases “in certain embodiments,” “in some embodiment,” “in other embodiments,” or similar language throughout this specification do not necessarily all refer to the same group of embodiments and the described features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. 
         [0075]    It will be readily understood that the components of the present invention, as generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of the embodiments of the apparatus, system, and method of the present invention, as represented in the attached figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention.