If an INVITE contains an initial offer, per RFC3261 "the answer MUST be in a reliable non-failure message from UAS back to UAC.... The UAC MUST treat the first session description it receives as the answer, and MUST ignore any session descriptions in subsequent responses to the initial INVITE."
Say a UAS for basic telephony sends back 180 Ringing without SDP when it receives INVITE with SDP to cause local ringing. Then the UAS would send 200 OK with SDP for the INVITE when call answers. So does this mean that if an INVITE contains an SDP offer with support for reliable provisional response, the UAS cannot send SIP 180 response without SDP as a reliable provisional response (RFC3262)? This implies that first reliable response must carry the SDP answer. Or does it mean that 180 can still be sent reliably, and the lack of SDP in 180 will cause UAC to wait for SDP answer in some subsequent response, and PRACK must not contain SDP? Thus implying that first reliable response does not have to carry the SDP answer. _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
