I wrote a few days ago about Media Formats and priorities within Session Description Protocol (SDP) payload.
Something that occasionally comes up is the ability to delay the SDP information so that it is not contained within the INVITE message. This is known as Delayed Offer. In this scenario, the originator sends an INVITE message to the called party without the SDP information. The called party then responds with an 200 OK message which then contains the SDP information. The originating device can then respond with an ACK confirming SDP agreement parameters.
Dialogic have already created a good call flow showing this.
At the time of writing this, I’ve not seen this capability on Avaya platforms, but have seen it as an option on Cisco UCM. Let me know if Avaya have included this capability and I’ve missed it.