SIP 480 Temporarily Unavailable

What SIP 480 means

The extension exists but nothing is available to ring. On a hosted system this nearly always means the handset is not registered, which is why a 480 so often follows a router reboot, a broadband fault or a firewall change.

Client error (4xx)
Sent by The destination PBX or registrar
Common

What SIP 480 Temporarily Unavailable actually means

The destination was contacted successfully but is temporarily unavailable, and the server may suggest when to try again using a Retry-After header. The word temporarily matters: unlike a 404, the address is valid and the system expects it to work again.

What causes SIP 480 on a business phone system

No device is registered to the extensionThe single most common cause. A phone that has lost registration is invisible to the PBX, so calls to it have nowhere to go. Registration is usually lost after a router reboot, a broadband dropout, or a firewall change that closes the port the phone was using.
Do Not Disturb is switched onDND is easy to enable by accident with a mis-press, and on many handsets the on-screen indication is subtle. Worth ruling out before any network investigation, because it costs seconds.
An out-of-hours or time-based rule has no destinationA schedule that routes calls somewhere undefined outside working hours produces a 480 rather than an obvious error, and it only shows up at the times nobody is testing.
SIP ALG on the router is breaking registrationA router rewriting SIP headers can leave the PBX believing a phone is registered at an address that no longer reaches it. Registration looks fine from one side and calls still fail.
The registration expiry is longer than the NAT timeoutIf the phone only refreshes every hour but the router closes the pinhole after a few minutes, the phone thinks it is registered while inbound calls cannot reach it. Typically shows up as outbound working and inbound failing.

How to fix SIP 480

Check the registration status in your provider portalLook at whether the extension shows as registered and when it last checked in. This one reading tells you whether to investigate the phone and network or the call routing, and it takes a moment.
Rule out Do Not Disturb on the handsetCheck the display for a DND icon and switch it off. Also check for a forwarding rule set on the handset itself rather than in the platform.
Disable SIP ALG on the routerSIP ALG is the most common network cause of registration that appears healthy but does not work. It is enabled by default on a lot of consumer routers and should be switched off wherever a phone system is in use.
Shorten the registration intervalBring the registration expiry below the router NAT timeout, commonly to 120 or 180 seconds, so the pinhole is refreshed before it closes. Enable keep-alive on the handset if it offers it.
Check time-based routing if it only happens at certain hoursConfirm every branch of an out-of-hours rule has a real destination, including the branch nobody tests.

Fixing the underlying problem

This page explains the code. These guides walk through the fix in detail.

Questions about SIP 480

What does SIP 480 Temporarily Unavailable mean?

The extension you dialled is valid but there is nothing available to ring. On a hosted phone system that almost always means no handset is currently registered to it, though Do Not Disturb and out-of-hours rules produce the same response.

Why do I get 480 after rebooting my router?

Because the phones lost their registration when the connection dropped and something is stopping them getting it back. Check whether the extension shows as registered, then disable SIP ALG on the new or restarted router, as that is the usual culprit.

What is the difference between SIP 480 and SIP 486?

A 486 means the phone is there and busy on a call. A 480 means nothing is reachable to ring in the first place. Busy is a working system, unavailable usually is not.

Why can I call out but not receive calls?

That pattern points at the registration path rather than the phone. Outbound calls work because the phone opens the connection itself, while inbound calls need the provider to reach the phone through your router. A registration interval longer than the router NAT timeout, or SIP ALG, will produce exactly this.

Call hangup causes that become SIP 480

If the call crossed a gateway between SIP and ISDN or SS7, this status may have started life as one of these Q.850 cause values. The mapping is defined in RFC 3398 section 7.2.4.1.

Related SIP response codes

Source. SIP 480 Temporarily Unavailable is defined in RFC 3261 section 21.4.18 and registered in the IANA SIP Parameters — Response Codes. The causes and fixes above are drawn from our own experience supporting UK business phone systems.

All VoIP & SIP codes