When it happens
- Session-Expires lower than the peer’s Min-SE, often 90 versus 1800 seconds.
What to check
- Raise Session-Expires on your side to at least the Min-SE value in the response, or disable session timers.
What the response looks like
SIP/2.0 422 Session Interval Too Small
Via: SIP/2.0/UDP 203.0.113.10:5060;branch=z9hG4bK776asdhds
From: <sip:101@pbx.example>;tag=1928301774
To: <sip:+15551234567@pbx.example>;tag=a6c85cf
Call-ID: a84b4c76e66710@203.0.113.10
CSeq: 2 INVITE
Content-Length: 0