Section: 5.2.4.3 Traffic channel assignment and user connection attachment
Content: An appropriate traffic channel for the call is assigned in SRVCC handover, vSRVCC handover or 5G-SRVCC handover from NG-RAN to UTRAN. For SRVCC handover or 5G-SRVCC handover from NG-RAN to UTRAN, the mobile station shall attach the user connection: - when the call control entity enters the "active" state or the "call received" state; - when the call control entity enters the "call delivered" state, if prior to SRVCC the MS in the PS domain was receiving media for the session subjected to SRVCC handover or 5G-SRVCC handover from NG-RAN to UTRAN; and - when the call control entity enters the "mobile originating call proceeding" state, if prior to SRVCC the MS in the PS domain was receiving media for the session subjected to SRVCC handover5G-SRVCC handover from NG-RAN to UTRAN. NOTE: The attachment of the user connection prior to entering the "active" state allows the network to provide in-band tones and announcements to the UE. For vSRVCC handover, the mobile station shall attach the user connection when the call control entity enters the "active" state. For SRVCC or vSRVCC handover to a speech call, the principles of speech codec selection are described in subclause 5.2.1.11. For vSRVCC handover to a circuit-switched multimedia call, further requirements are specified in subclause 5.3.6.6.