Subject: [BLISS] 3GPP requirements for suspend/resume procedures on the call-completion internet draft

From: "Huelsemann, Martin" <[email-masked]>
Date: Fri, 7 Nov 2008 12:03:32 +0100

Dear colleagues,

as suggested at the last IETF - 3GPP conference call, a short summary of the 3GPP requirements regarding call-completion would be useful, here it is:

3GPP is describing an IMS call-completion service in 3GPP TS 24.642. The basis for the 3GPP specification is draft-ietf-bliss-call-completion, describing the framework for call-completion and defining the required protocol elements.

The 3GPP service description for inter alia the call-completion service is given in 3GPP TS 22.173. For this TS 22.173 refers to the service description of the original ISDN service, in case of CCBS this is ETSI EN 300357. EN 300357 describes the suspension of the CCBS request in case the invoking user is busy when receiving the CCBS recall, which means we have the requirement for suspend and resume procedures for the procedures of TS 24.642. 

[suspension shortly: user A activates CC and is queued on the B side; then user B becomes available and user A is informed to start the CC call; but user A is busy now, so his queue entry is suspended until he becomes not busy, but he doesn't loose his position in the B queue]

One of the reasons why 3GPP has chosen the same service description like the PSTN/ISDN call-completion service was to be fully compatible with existing PSTN call-completion implementations. Those existing implemetations use explicit activation, deactivation, suspension and resumption requests. As PSTN gateways are not stateful and just interwork CC requests, there is also the requirement for the 3GPP IMS call-completion service for explicit suspend and resume requests (that is why the proposal to just un-subscribe in case of suspension and re-subscribe in case of resumption is not sufficient for the 3GPP call-completion solution).

>From 3GPP perspective it would be very helpful to have the whole CC framework in one IETF draft. But it would also be sufficient if sus/res procedures in the CC internet draft are designed optional: that could be a very basic solution without sus/res, an internet solution with sus/res basing on un-subscribe/re-subscribe, and a more complex PSTN interworkable solution basing on re-using presence information.

BR, Martin

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