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408
4xx Client error, RFC 3261

SIP 408 Request Timeout

SIP 408 Request Timeout means no final answer arrived in time: the far phone or network did not respond, or your system could not reach the next server.

Who sends it
The called side
When
Placing the call (INVITE)
Retry?
Once, after a short wait. Repeated 408s point to a network problem to fix first.
The caller hears
Silence or ringing for a while, then a failure tone.
PBXYour phone or PBX
SIPThe SIP trunk
☎The called sidesends 408
FIX

What causes 408, and how to fix it

408 means a server gave up waiting. On trunks it usually points at the network path: packets lost, blocked, or sent to an address that never answers.

  1. 1
    Most common

    The called phone or network did not respond in time, for example a mobile switched off or out of coverage.

    Try again later, or call another number to see whether the problem follows one destination.

  2. 2
    Most common

    Your PBX cannot reach the trunk at all, so it times out and creates the 408 itself.

    Check the trunk registration status, that the server name resolves, and that outbound SIP is allowed by your firewall.

  3. 3
    Sometimes

    Replies from the trunk come back to a port your router has already closed.

    Turn off SIP ALG, and enable keep-alives (often called qualify or NAT keep-alive) on the trunk.

  4. 4
    Sometimes

    Large SIP messages are fragmented and the fragments are dropped, often over a VPN.

    Avoid sending SIP through a VPN, and trim unused codecs from the offer to keep messages small.

LOG

What 408 looks like in a SIP log

SIP/2.0 408 Request Timeout

Capturing one: reading the SIP log.

SIP response
SIP/2.0 408 Request Timeout
Via: SIP/2.0/UDP 203.0.113.10:5060;branch=z9hG4bK-74bf9
Call-ID: [email protected]
≠

Not to be confused with

408, 480, 503 or 504?

480

Temporarily Unavailable

The callee was reached and is unavailable. 408 means no answer came back at all.

503

Service Unavailable

A server answered that it cannot take the call now. 408 is the absence of an answer.

504

Server Time-out

A server timed out waiting for the next server. 408 is the request itself timing out.

FAQ

SIP 408 questions

Who sends a SIP 408?
Either a server that gave up waiting for the called party, or your own phone system when it never heard back from the trunk. The trunk registration status tells you which.
Is SIP 408 my fault?
Sometimes. If every call times out, the cause is usually on your side: network, firewall or NAT. If only some destinations time out, the far network is the usual cause.

Not 408? Look up another code.

The full list: SIP response codes. 408 again and again? Check your SIP trunk configuration.

All SIP codesFind a fault by symptom