408 4xx Client error RFC 3261
SIP 408 Request Timeout
The server could not produce a response in time, for example because the user could not be located or no answer came from downstream.
Typical Q.850 / ISDN cause: 102 (Recovery on timer expiry)
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Common causes
- The far end is unreachable (firewall, NAT, wrong IP or port).
- Packets lost because of UDP fragmentation or a SIP ALG.
- A downstream proxy or carrier is not responding.
How to fix it
- Check whether requests leave your network, using sngrep or tcpdump on the public interface.
- Open UDP 5060 (or your SIP port) and RTP ranges on the firewall, and disable SIP ALG.
- Try TCP or TLS transport if large INVITEs are being fragmented.
Seeing 408 on calls through a router or firewall? Check that SIP ALG is disabled. It causes a surprising number of SIP errors. Read why.
About 4xx responses
The request has a problem or cannot be completed at this server, usually because of something on the requesting side or the target user.