scope:

Introduction

The Mobile Service Transport (MST) is defined by 3GPP TS 29.205 for use to signal the Mobile Equipment Identifier and numerous Local Call Local Switch IEs. Of particular interest is the use of the MST to carry the Mobile Equipment Identifier in support of Single Radio Voice Call Continuity (SRVCC) for LTE subscribers during emergency calls.

When an LTE subscriber emergency call hands over to circuit coverage while wanting to maintain VCC, the serving MSC needs to establish a call path into IMS to the IMS Emergency Access Transfer Function (EATF) currently supporting the call. In order to associate this new MSC call leg to the existing call, the MSC must provide the subscriber IMEI in the SIP Contact header. When the call path is using ISUP between the MSC and the MGCF, the subscriber IMEI is signaled in the ISUP Application Transport parameter. (See 3GPP TS 29.163, subclause 7.2.3.2.2C, for interworking.)

The Application Context Identifier is used to indicate the nature of the Application Transport parameter. 3GPP TS 29.205 has defined this MST usage and the identifier code point of "000111" has been defined.