M.2 5GS aspects when connected to the IM CN subsystem

24.1733GPPIMS Multimedia telephony communication service and supplementary servicesRelease 18Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

M.2.1 Procedures at the UE

M.2.1.1 Indications to lower layers about start and stop of MMTEL sessions

The following information is provided to the non-access stratum:

– MO-MMTEL-voice-started;

– MO-MMTEL-voice-ended;

– MO-MMTEL-video-started;

– MO-MMTEL-video-ended;

– MT-MMTEL-voice-started;

– MT-MMTEL-voice-ended;

– MT-MMTEL-video-started;

– MT-MMTEL-video-ended;

– for 3GPP access only, handover of ongoing MMTEL voice call from non-3GPP access; and

– for 3GPP access only, handover of ongoing MMTEL video call from non-3GPP access.

Upon request from a user to establish an originating multimedia telephony communication session as described in clause 5.2:

1) if the multimedia telephony communication session to be established is an emergency session, then skip the rest of steps below and continue with session establishment as described in clause 5.2;

2) if only audio or only real-time text or only both audio and real-time text (see clause 4.2 for 3GPP systems) are offered in the multimedia telephony communication session, and no other originating multimedia telephony communication session initiated with offering only audio or only real-time text or only both audio and real-time text exists, the UE sends the MO-MMTEL-voice-started indication to the non-access stratum and

a) if the barring result is "not-barred", continue with session establishment as described in clause 5.2; and

b) if the barring result is "barred", reject the multimedia telephony communication session establishment and skip the rest of steps below; and

3) if video is offered in the multimedia telephony communication session, and no other originating multimedia telephony communication session initiated with offering video exists, the UE sends the MO-MMTEL-video-started indication to the non-access stratum and

a) if the barring result is "not-barred", continue with session establishment as described in clause 5.2; and

b) if the barring result is "barred", reject the multimedia telephony communication session establishment and skip the rest of steps below.

NOTE: Adding or removing media during the multimedia telephony communication session is not subject to unified access control.

When a terminating multimedia telephony communication session starts (i.e. an INVITE is received), the terminating multimedia telephony communication session is offering only audio or only real-time text or only both audio and real-time text (i.e. in the SDP offer in the INVITE request), and no other terminating multimedia telephony communication session started with offering only audio or only real-time text or only both audio and real-time text exists, the UE sends the MT-MMTEL-voice-started indication to the non-access stratum.

When a terminating multimedia telephony communication session starts (i.e. an INVITE is received), the terminating multimedia telephony communication session is offering video (i.e. in the SDP offer in the INVITE request), and no other terminating multimedia telephony communication session started with offering video exists, the UE sends the MT-MMTEL-video-started indication to the non-access stratum.

When an originating multimedia telephony communication session ends (i.e. a response to a BYE or a failure response to the initial INVITE request is transferred), the originating multimedia telephony communication session was initiated with offering only audio or only real-time text or only both audio and real-time text (i.e. in the SDP offer in the initial INVITE request), and no other originating multimedia telephony communication session initiated with offering only audio or only real-time text or only both audio and real-time text exists, the UE sends the MO-MMTEL-voice-ended to the non-access stratum.

When an originating multimedia telephony communication session ends (i.e. a response to a BYE or a failure response to the initial INVITE request is transferred), the originating multimedia telephony communication session was initiated with offering video (i.e. in the SDP offer in the initial INVITE request), and no other originating multimedia telephony communication session initiated with offering video exists, the UE sends the MO-MMTEL-video-ended indication to the non-access stratum.

When a terminating multimedia telephony communication session ends (i.e. a response to a BYE or a failure response to the initial INVITE request is transferred), the terminating multimedia telephony communication session was initiated with offering only audio or only real-time text or only both audio and real-time text (i.e. in the SDP offer in the initial INVITE request), and no other terminating multimedia telephony communication session initiated with offering only audio or only real-time text or only both audio and real-time text exists, the UE sends the MT-MMTEL-voice-ended indication to the non-access stratum.

When a terminating multimedia telephony communication session ends (i.e. a response to a BYE or a failure response to the initial INVITE request is transferred), the terminating multimedia telephony communication session was initiated with offering video (i.e. in the SDP offer in the initial INVITE request), and no other terminating multimedia telephony communication session initiated with offering video exists, the UE sends the MT-MMTEL-video-ended indication to the non-access stratum.

When an ongoing originating multimedia telephony communication session is handed over from non-3GPP access to 3GPP access:

1) if only audio or only real-time text or only both audio and real-time text (see clause 4.2 for 3GPP systems) are used in the multimedia telephony communication session, the UE sends the MO-MMTEL-voice-started indication and the handover of ongoing MMTEL voice call from non-3GPP access indication to the non-access stratum; and

2) if video is used in the multimedia telephony communication session, the UE sends the MO-MMTEL-video-started indication and the handover of ongoing MMTEL video call from non-3GPP access indication to the non-access stratum.

When an ongoing terminating multimedia telephony communication session is handed over from non-3GPP access to 3GPP access:

1) if only audio or only real-time text or only both audio and real-time text (see clause 4.2 for 3GPP systems) are used in the multimedia telephony communication session, the UE sends the MT-MMTEL-voice-started indication and the handover of ongoing MMTEL voice call from non-3GPP access indication to the non-access stratum; and

2) if video is used in the multimedia telephony communication session, the UE sends the MT-MMTEL-video-started indication and the handover of ongoing MMTEL video call from non-3GPP access indication to the non-access stratum.

M.2.1.2 MMTEL request timeouts

If the UE supports timer RequestTimeout, then upon a request from a user to establish an originating multimedia telephony communication session as described in clause 5.2, the UE shall start timer RequestTimeout when sending an initial INVITE request.

The UE may support being configured for the RequestTimeout timer with the operator’s IMS multimedia telephony communication service policy as specified in 3GPP TS 24.275 [36].

M.2.1.2A Registration and authentication

If:

a) the UE includes a "+g.3gpp.icsi-ref" header field parameter equal to "urn:urn-7:3gpp-service.ims.icsi.mmtel" in the Contact header field of the SIP REGISTER request; and

b) the IP-CAN of 5GS indicated that interworking without N26 is supported as specified in 3GPP TS 24.501 [42];

the UE should include a transport=tcp URI parameter in the Contact header field of the SIP REGISTER request.

NOTE 1: The UE includes a transport=tcp parameter to ensure that the P-CSCF uses TCP connection when it receives an initial request for a dialog or a request for a standalone transaction destined for the UE. The use of TCP is to ensure the reception of transmitted SIP messages in case fallback to EPS for voice is used and the IP-CAN of 5GS supports interworking without N26.

If:

a) the UE changes from another IP-CAN to an IP-CAN of 5GS; and

b) the IP-CAN of 5GS indicated that interworking without N26 is supported as specified in 3GPP TS 24.501 [42];

the UE may perform re-registration of a previously registered public user identity bound to the other IP-CAN. In this case, if the UE includes a "+g.3gpp. icsi-ref" header field parameter equal to "urn:urn-7:3gpp-service.ims.icsi.mmtel" in the Contact header field of the SIP REGISTER request, the UE should include a transport=tcp URI parameter in the Contact header field of the SIP REGISTER request.

NOTE 2: This document does not specify how the UE detects that the used IP-CAN has changed.

NOTE 3: The UE can send the reregistration request irrespective of whether or not it has established a SIP dialog.

M.2.1.3 Abnormal cases

Upon request from a user to establish an MMTEL voice or an MMTEL video session as described in clause 5.2, if

a) the UE receives, from the lower layers, a notification that the service request

1) was not accepted due to congestion; or

2) resulted in starting timer T3525 (see 3GPP TS 24.501 [42]); and

b) an originating initial INVITE transaction, for which a 2xx response has not yet been received, exists;

then:

a) if a provisional response has been received, the UE shall cancel the INVITE transaction; and

b) if an alternative radio access network is available, the UE shall attempt the MMTEL voice or an MMTEL video session on the alternative radio access network.