A.24 UE putting a Video Call on hold or resume the call / 5GS

34.229-53GPPInternet Protocol (IP) multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP)Part 5: Protocol conformance specification using 5G System (5GS)Release 16TSUser Equipment (UE) conformance specification

Expected sequence

Step	Direction		Message	Comment
	UE	SS
1	—>		INVITE or UPDATE	UE sends INVITE or UPDATE with a SDP offer to hold or resume the call
2	<–		100 Trying	The SS responds to the INVITE with a 100 Trying provisional response
3	<–		200 OK	The SS responds to INVITE or UPDATE with 200 OK to indicate that the remote UE is no more sending any media (call hold) or resumes sending media (call resume)
4	–>		ACK	Conditional: If the UE sent INVITE in step 1 then UE acknowledges the receipt of 200 OK for INVITE

Specific Message Contents

INVITE or UPDATE (Step 1)

Use the default message “INVITE for MO call setup” in Annex A.2.1 of TS 34.229-1 [2] applying conditions A1, A3, A5, A10, A11 and A28 or “UPDATE” in Annex A.2.5 applying conditions A1 and A6 of TS 34.229-1 [2]. In case of an INVITE the UE shall use also the same URI in the request line as the SS has sent in the Contact header of an earlier message within the same dialog (in case of an UPDATE ref. to A.2.5 of TS 34.229-1 [2]).

The UE shall include support for precondition in the Supported header field.

The UE shall include an SDP body as described in A.15.1, Step 6, but with the following exceptions and clarifications:

– the sess-version number of the SDP shall be incremented by one; and

– the direction-tag for the current-status remote segment shall be "sendrecv"; and

– the UE shall either add a session level direction attribute (and remove the direction attributes of all the media lines) or modify the direction attributes of all the media lines as follows:

– in case of Call Hold

– If the directionality of the media lines were originally as "recvonly" then the directionality attributes within the INVITE in step 1 shall be "inactive"

– If the directionality of the media lines were originally as "sendrecv" then the directionality attributes within the INVITE in step 1 shall be "sendonly"

– in case of Call Resume

– the UE shall restore the value of the directionality attributes within the SDP body their original values (the UE may use either a single session level attribute or separate attributes for each media line).

100 Trying for INVITE (Step 2) optional step used when UE sent INVITE in step 1

Use the default message “100 Trying for INVITE” in Annex A.2.2 of TS 34.229-1 [2], applying condition A1.

200 OK for INVITE or UPDATE (Step 3)

Use the default message “200 OK for other requests than REGISTER or SUBSCRIBE” in Annex A.3.1 of TS 34.229-1 [2], applying conditions A1, A10 and A19, with the following exceptions:

Header/param	Value/remark
Require
option-tag	precondition
Content-Type
media-type	application/sdp
Content-Length
value	length of message-body
Message-body	SDP body of the 200 OK response copied from the received INVITE or UPDATE but modified as follows: – "o=" line identical to previous SDP sent by SS except that sess-version is incremented by one – IP address on "c=" line and transport port on "m=" lines changed to indicate to which IP address and port the UE should send the media; and In case of Call Hold: – "sendonly" direction attribute inverted to "recvonly". Note that this applies to “a=sendonly” direction attributes only, not to the direction tags found in preconditions.

ACK (Step 4) conditional step used when UE sent INVITE in step 1

Use the default message “ACK” in Annex A.2.7 of 34.229-1 [2], applying conditions A1, A3 and A5.