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SIP response codes

SIP 480 Temporarily Unavailable

Temporarily Unavailable: the user exists but cannot take calls right now.

480

Name: Temporarily Unavailable
Class: 4xx · Client error
Defined in: RFC 3261
Q.850 cause towards the PSTN: 18 · No user responding
Produced from Q.850 causes: 19, 20, 31

When it happens

The phone is not registered (offline, out of coverage, app closed on a mobile).
Do Not Disturb is on.
The callee did not answer within the timeout and there is no voicemail.

What to check

Check the registration status of the called extension.
On mobile softphones, check push notifications and battery-saving settings that kill the app.

What the response looks like

SIP/2.0 480 Temporarily Unavailable
Via: SIP/2.0/UDP 203.0.113.10:5060;branch=z9hG4bK776asdhds
From: <sip:101@pbx.example>;tag=1928301774
To: <sip:+15551234567@pbx.example>;tag=a6c85cf
Call-ID: a84b4c76e66710@203.0.113.10
CSeq: 2 INVITE
Reason: Q.850;cause=18;text="No user responding"
Content-Length: 0