504 5xx Server error RFC 3261
SIP 504 Server Time-out
A server acting as gateway did not get a timely response from the next hop (or DNS).
Typical Q.850 / ISDN cause: 102 (Recovery on timer expiry)
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Common causes
- Downstream server not responding, or a DNS lookup timing out.
How to fix it
- Check the reachability and DNS resolution of the next hop. Check your DNS servers.
Seeing 504 on calls through a router or firewall? Check that SIP ALG is disabled. It causes a surprising number of SIP errors. Read why.
About 5xx responses
The server failed to handle an apparently valid request.