SIP transfer fails against a multi-hop proxy (Avaya SM) — REFER's Route header points back at LiveKit-SIP itself

[amr-imad]

What we're seeing

When an inbound call arrives through a proxy that inserts multiple Record-Route entries (Avaya Session Manager, in our case), a subsequent TransferSipParticipant call fails every time. The REFER LiveKit-SIP sends out carries a Route header pointing back at LiveKit-SIP's own address instead of the proxy's. The proxy dutifully routes the request back to us, we don't recognize it as a valid inbound request, and reject it with 405 Method Not Allowed — so the transfer never completes.

Transfers work fine against a direct SIP peer with no proxy in the signaling path.

Example

# INVITE Record-Route (from the proxy, PROXY_IP = Avaya Session Manager)
Record-Route: <sip:PROXY_IP;transport=tcp;lr>

# Our outgoing REFER — should route back through PROXY_IP, but instead:
Route: <sip:LIVEKIT_SIP_IP;transport=tcp;lr>

What we've tried

Same failure in every combination we tested:

Version	add_record_route	Result
Older production build	default	Fails, same Route bug
v1.8.0	default	Fails, same Route bug
v1.8.0	true	Fails, same Route bug

Happy to help

We have full sanitized SIP captures (INVITE/REFER/logs) from a real production reproduction if that's useful for tracking this down.

[amr-imad]

Looks like this is the same root cause as #642 (different trunk provider, BYE instead of REFER, but the same self-referencing Route/Record-Route behavior) — good independent confirmation this isn't Avaya-specific.

There's also a draft fix here that addresses both issues: lixuanqun#5 — rebuilds the UAS route set from the original INVITE's Record-Route (RFC 3261 §12.1.1) instead of trusting whatever got copied onto the outgoing request. Not yet opened against this repo or reviewed, but wanted to flag it in case it's useful.

Would appreciate a maintainer look when possible — happy to test a fix against our production trunk if that helps move it along.

cc @alexlivekit @hechen-eng @livekit/telephony-devs