Symptom
For SIP-to-nonIP calls IOS XE voice gateway replies to initial SIP INVITE/wSDP with 'a=sendonly' with 200 OK/wSDP with no direction attribute (implying default 'a=sendrecv').
According to RFC3264 it must include 'a=recvonly' or 'a=inactive':
If a stream is offered as sendonly, the corresponding stream MUST be
marked as recvonly or inactive in the answer.
The issue is not present in case of SIP-to-SIP calls.
For mid-call media re-negotiations 'a=sendonly' is handled properly.
This behavior may cause one-way audio issues for certain call scenarios.
Conditions
- calls from SIP to non-IP call leg, for example:
SIP >> VGW >> PRI
- 'a=sendonly' in initial INVITE with SDP offer
