How are SIP response codes structured?

SIP borrows HTTP's six-class model. 1xx are provisional (the request is in progress, like 180 Ringing), 2xx are success (200 OK answers a call), 3xx are redirection, 4xx are client or request errors at this server, 5xx are server failures, and 6xx are global failures that apply to the whole call across every endpoint.

What is the difference between SIP 486 and 600?

486 Busy Here means the callee is busy at this particular endpoint, so a forking proxy may still try other registered devices. 600 Busy Everywhere is a global failure declaring the callee busy at all endpoints, which tells the proxy to stop forking and not try any alternative locations.

Why do I see 487 Request Terminated?

487 means the INVITE transaction was terminated before it completed, almost always because a CANCEL was sent (the caller hung up while it was still ringing) or another branch of a forked call answered first. It is a normal part of call cancellation, not an error to debug.

What does 480 Temporarily Unavailable mean?

480 means the callee's location was found but the user cannot be reached right now, for example because they are offline, in do-not-disturb mode, or registration has expired. Unlike 404 Not Found, the address is valid; the user is simply unavailable at this moment, so a retry later may succeed.

Is this SIP reference private?

Yes. The full response-code table, search and filtering run locally in your browser with no account and no network calls. Nothing you type is sent anywhere.

SIP Response Codes Reference

The SIP Response Codes Reference is a searchable lookup for the response codes carried by the Session Initiation Protocol, the signalling layer behind VoIP calls, video conferencing and messaging. From 100 Trying to 486 Busy Here to 604 Does Not Exist Anywhere, this tool decodes every code with its reason phrase, class and the call-flow context you need when reading a SIP trace.

How it works

SIP, defined in RFC 3261, deliberately mirrors HTTP’s status-code model with six classes keyed off the first digit:

1xx  Provisional  — request received, still processing (180 Ringing)
2xx  Success      — request succeeded (200 OK answers the call)
3xx  Redirection  — try a new location (302 Moved Temporarily)
4xx  Client error — request failed at THIS server (486 Busy Here)
5xx  Server error — this server failed (503 Service Unavailable)
6xx  Global       — failure for the WHOLE call (600 Busy Everywhere)

The crucial SIP-specific distinction is between 4xx and 6xx. When a proxy forks an INVITE to several registered devices, a 4xx rejects only that one branch, so other devices may still answer. A 6xx is authoritative for the entire call — it tells the proxy to abandon every branch. This tool keeps the full table in your browser and filters it by number, reason or keyword.

Example and tips

A successful call signals 100 Trying → 180 Ringing → 200 OK → ACK. A declined call might go 100 Trying → 180 Ringing → 603 Decline. When you see 487 Request Terminated, look for a matching CANCEL — it usually means the caller gave up while ringing, not a fault. Treat 488 Not Acceptable Here and 415 Unsupported Media Type as codec/SDP negotiation problems, and 407 Proxy Authentication Required as the normal challenge step before a registrar or proxy accepts your request.

SIP Response Codes Reference

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How it works

Example and tips