SIP 480 Temporarily Unavailable means the server knows who you're trying to reach but they're not available right now. It's different from busy (486), not found (404), or a network failure (408). Here's what causes it and how to fix it.
SIP 480 Temporarily Unavailable is defined in RFC 3261 Section 21.4.18. It means the callee's end system was contacted but the callee is currently unavailable. The server is reachable, the user is known, but they can't accept calls right now.
The "temporarily" is important — 480 implies the situation is transient and a retry might succeed. The optional Retry-After header indicates how long to wait before retrying.
| Code | Meaning | Cause |
|---|---|---|
| 480 | Temporarily Unavailable | User known, not available right now (DND, not registered, offline) |
| 486 | Busy Here | User known and registered, actively on another call |
| 404 | Not Found | User or domain doesn't exist on this server |
| 408 | Request Timeout | No response — network or connectivity issue |
| 603 | Decline | User explicitly rejected the call |
Step 1 — Check registration status. On Asterisk: sip show peers or pjsip show contacts. Look for the extension — is it registered? When did it last register? What IP did it register from?
Step 2 — Check DND status. On most PBX systems: database get DND 1001 (replace 1001 with extension). If DND is set, the value will be YES.
Step 3 — Trace the INVITE. Enable SIP debug and make a test call. Look for where the 480 originates — does it come from the PBX itself (extension not registered) or does it come back from the endpoint (DND or reject)?
Step 4 — Check call forwarding. Review the extension's forwarding settings in the PBX. If forwarding is enabled, trace where the forwarded call goes and whether that destination is reachable.
Extension not registered: Check network connectivity from the phone. Verify SIP server address, port, and credentials in the phone config. Check that the registration expiry is set appropriately (120-3600 seconds). Look for firewall rules blocking registration renewals.
DND enabled: Disable DND on the phone or via PBX admin interface. On Asterisk: database del DND 1001.
Registration expiry: Increase registration expiry interval on both the phone and PBX. Set minimum expiry to 120 seconds. Enable register retry on registration failure.
Call forwarding loop: Review and simplify forwarding chains. Ensure all forwarding destinations are reachable. Set a maximum forwarding depth to prevent infinite loops.
SIP 480 means the server knows the user you're trying to reach but they are currently unavailable — not registered, in DND mode, or their endpoint is offline. Unlike 486 (actively busy on a call) or 404 (user doesn't exist), 480 means the user exists but can't accept calls right now.
SIP 480 Temporarily Unavailable means the endpoint is not registered or not available — the phone may be offline, in DND, or the registration expired. SIP 486 Busy Here means the endpoint is registered and active but currently engaged in another call. Both indicate the user cannot take the call, but for different reasons.
To fix SIP 480: check that the extension is registered (sip show peers or pjsip show contacts in Asterisk), verify DND is not enabled (database get DND 1001), confirm the phone has network connectivity and valid credentials, and check that registration expiry is set to at least 120 seconds with automatic re-registration enabled.
Paste your SIP trace into SIPSymposium. The analyzer identifies whether 480 is coming from the PBX or endpoint, checks registration state, and identifies DND and forwarding issues.