7.1 General

23.2313GPPRelease 17SIP-I based circuit-switched core networkStage 2TS

The terms "incoming" and "outgoing" in the following text refers to the direction of propagation of the release indication, not to the direction of original call establishment.

During call establishment, the call may be released by sending a BYE or CANCEL request in the direction of the original call establishment, or by a failure response in the opposite direction of the original call establishment. For an established call, the call may be released by BYE request in the direction of the original call establishment or in the opposite direction of the original call establishment.

The term "release indication" in the following text refers to any message which is to release the call, i.e. it may be the BYE or CANCEL request, or the failure response to the initial INVITE request.

In accordance with ITU-T Q.1912.5 [9] Profile C, the generation of:

– a BYE request and a 4xx, 5xx, 6xx final response to initial INVITE should encapsulate an ISUP REL message.

NOTE: there can be cases where it may not be possible to encapsulate an ISUP REL due to some specific error scenarios. Additionally it is possible that an IWU forwards a BYE or a 4xx, 5xx, 6xx final response without a REL.

– a 200 OK final response to a BYE request shall encapsulate an ISUP RLC message if a BYE is received with an encapsulated REL.

The user initiated call clearing shall be performed in accordance with 3GPP TS 23.108 [18].

NOTE: All message sequence charts in this clause are examples. All valid call clearing message sequences can be derived from the example message sequences and associated message pre-conditions.