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Content for  TR 23.870  Word version:  9.0.0

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1…   6… 
1 Scope  2 References  3 Definitions and abbreviations  4 Overall Requirements  5 Scenarios 
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1  Scope  p. 5

SRVCC as specified in TS 23.216, provides handover of voice calls from E-UTRAN/HSPA to UTRAN/GERAN or from E-UTRAN to CDMA2000 1x. SRVCC of IMS emergency calls is not supported in TS 23.216, and thus handover of such calls will have unpredictable effects, in the worst case causing the call to fail. This is a serious concern for operators and their subscribers, and may cause regulatory violations in some parts of the world.
Therefore, the objective of this document is to study both the EPS and IMS aspects of how to best support the handover of ongoing emergency calls for the following scenarios:
  • E-UTRAN to UTRAN/GERAN CS.
  • HSPA to UTRAN/GERAN CS.
  • E-UTRAN to CDMA2000 1x CS.
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    2  References  p. 5

    The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
    • References are either specific (identified by date of publication, edition number, version number, etc.) or non specific.
    • For a specific reference, subsequent revisions do not apply.
    • For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
    [1]
    TR 21.905: "Vocabulary for 3GPP Specifications".
    [2]
    TR 23.869: "Support for IMS Emergency Calls over GPRS and EPS".
    [3]
    TS 23.216: "Single Radio Voice Call Continuity (SR VCC); stage 2".
    [4]
    TS 23.237: "IP Multimedia Subsystem (IMS) Service Continuity; Stage 2".
    [5]
    TS 23.167: "IP Multimedia Subsystem (IMS) emergency sessions".
    [6]
    TR 23.891: "Evaluation of LCS Control Plane Solutions for EPS".
    [7]
    TS 24.229: "IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3".
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    3  Definitions and abbreviations  p. 5

    3.1  Definitions  p. 5

    For the purposes of the present document, the terms and definitions given in TR 21.905 and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in TR 21.905.
    Single Radio Voice Call Continuity (SR VCC):
    see TS 23.216.
    Emergency Session Transfer Number for SR VCC:
    A number used in the session transfer procedure for emergency calls, pointing toward the serving (visited if roaming) IMS E-SCC AS which handles the IMS emergency session transfer from PS to CS access.
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    3.2  Abbreviations  p. 6

    For the purposes of the present document, the abbreviations given in TR 21.905 and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905.
    E-STN-SR
    Emergency Session Transfer Number for SR VCC
    E-SCC AS
    Emergency Service Centralization and Continuity Application Server

    4  Overall Requirements  p. 6

    4.1  Service Characteristics  p. 6

    4.2  Architectural Requirements  p. 6

    1. The transport layer aspects of the solution shall be based on SRVCC procedures specified in Rel 8 TS 23.216 - Single Radio Voice Call Continuity (SR VCC).
    2. The IMS aspects of the solution shall be aligned with the conclusions of the study in TR 23.868 Extended Support of IP Multimedia Subsystem (IMS) Emergency Sessions where appropriate.
    3. The solution should be able to provide continuity of location support following SR VCC of emergency calls by providing the PSAP with an accurate initial and updated location estimate, according to applicable regional requirements and subject to the constraints of the PSAP interface.
    4. The solution shall provide a mechanism to perform session transfer for UEs in limited service mode and prohibit when necessary, according to local regulations.
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    5  Scenarios  p. 6

    5.1  SR VCC from E-UTRAN (or HSPA) to 3GPP 2/3G  p. 6

    5.1.1  Use case #1  p. 6

    1. UE initiate IMS emergency session over EPS or UTRAN (HSPA). This solution will be defined as according to the outcome of TR 23.869 and TR 23.891.
    2. Visited IMS network is used for routing the session to PSAP. The SIP session is anchored in E-SCC AS.
    3. UE is moving out of E-UTRAN (or HSPA) coverage into 2/3G.
    4. SR VCC is performed and the UE is connected to 2/3G CS.
    5. Handover back to E-UTRAN (or HSPA) is not supported.
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    5.2  SR VCC from E-UTRAN to CDMA2000 1x  p. 7

    5.2.1  Use case #1  p. 7

    1. The UE initiates IMS emergency session over EPS. This solution will be defined as according to the outcome of TR 23.869.
    2. Visited IMS network is used for routing the session to PSAP. The SIP session is anchored in E-SCC AS similar to anchoring of session transfer in SCC AS, as specified in TS 23.237.
    3. The UE is moving out of E-UTRAN coverage to CDMA2000 1x network.
    4. SRVCC is performed and the UE is connected to CDMA 2000 1x network.
    5. Handover back to E-UTRAN is not supported.
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