6.3.1 GPRS Attach procedure for SRVCC

23.2163GPPRelease 16Single Radio Voice Call Continuity (SRVCC)Stage 2TS

GPRS attach procedure for 3GPP SRVCC UE is performed as defined in TS 23.060 [10] with the following additions:

– SRVCC UE includes the SRVCC capability indication as part of the "MS Network Capability" in the Attach Request message and in Routeing Area Updates. SGSN stores this information for SRVCC operation.

NOTE 1: If the service configuration on the UE is changed (e.g. the user changes between an IMS speech service supported by the home operator and a PS speech service incompatible with SRVCC), the UE can change its SRVCC capability indication as part of the "MS Network Capability" in a Routeing Area Update message.

– SRVCC UE includes the GERAN MS Classmark 3 (if GERAN access is supported), MS Classmark 2 and Supported Codecs IE in the Attach Request message and in the non-periodic Routeing Area Update messages.

NOTE 2: MS Classmark 2, MS Classmark 3, STN-SR, C‑MSISDN, ICS Indicator and the Supported Codec IE are not sent from the source SGSN to the target MME/SGSN at inter CN-node idle mode mobility.

– HSS includes STN-SR and C‑MSISDN as part of the subscription data sent to the SGSN. If the STN-SR is present, it indicates the UE is SRVCC subscribed. If a roaming subscriber is determined by the HPLMN not allowed to have SRVCC in the VPLMN then HSS does not include STN-SR and C‑MSISDN as part of the subscription data sent to the SGSN.

– SGSN includes a "SRVCC operation possible" indication in the RANAP Common ID message, meaning that both UE and SGSN are SRVCC-capable.

GPRS emergency attach procedure for 3GPP SRVCC UE is performed as defined in TS 23.060 [10] and above with the following clarifications:

– SRVCC UE shall include the SRVCC capability indication as part of the "MS Network Capability" in the Emergency Attach Request message and maintained during Routeing Area Updates. SGSN stores this information for SRVCC operation.