SIP Error 408 Request Timeout: Common Causes & Troubleshooting

Have you encountered a SIP 408 Request Timeout when trying to make or receive a VoIP call?

A SIP 408 response generally indicates that a SIP request did not receive a response within the expected time. However, the actual cause can vary depending on the PBX, SIP trunk, provider, network, firewall, NAT configuration, or the specific SIP request involved.

Some common areas worth checking when troubleshooting a SIP 408 Request Timeout include:

• SIP server or provider availability
• Network connectivity between the PBX and SIP provider
• Firewall rules blocking SIP traffic
• NAT configuration and public/private IP issues
• Incorrect SIP server or proxy configuration
• SIP transport settings such as UDP, TCP, or TLS
• SIP registration and keep-alive configuration
• RTP and SIP port configuration
• DNS or hostname resolution problems
• Packet loss, latency, or unstable network connections
• SBC or router configuration
• Provider-side connectivity or routing issues

When troubleshooting, checking the SIP trace or PBX logs can be particularly useful. Look at the request that receives the timeout and determine whether the request is leaving your PBX, reaching the provider, and whether any response is coming back.

For example, if a SIP INVITE is sent but no response is received, the problem could be somewhere between the PBX and the remote SIP endpoint. On the other hand, a timeout during registration may point toward a different connectivity or configuration issue.

Let's discuss

What has caused SIP 408 Request Timeout in your environment?

If you've dealt with this issue on Asterisk, FreePBX, FreeSWITCH, or another SIP/PBX system, share your experience below.

You can also share the relevant SIP response or log snippet, but please remove passwords, authentication credentials, phone numbers, public IP addresses, and other sensitive information before posting.

What was the cause in your case, and how did you troubleshoot it?