SIP Status Code of Response

When you troubleshoot PortSIP PBX issues, the specific cause of a call/request failure can be identified through the SIP response codes.

What are SIP response codes?

SIP Codes are pre-defined three-digit codes that convey critical status information when making a call.

The SIP response codes are defined in RFC 3261.

When making a phone call or establishing a communication session over SIP, a series of exchanges occur between the user agent sending the call request (called User Agent Clients or UAC) and the recipient’s server (called User Agent Servers or UAS). These exchanges are governed by a set of codes known as SIP response codes.

SIP codes are three-digit numbers that provide information about the status and progress of a SIP session. They serve as a common language that allows the various components of a communication system to communicate effectively and handle calls appropriately.

What do SIP codes look like?

SIP response codes are grouped into different categories, each with its own significance. They’re grouped by the first integer of the three-digit code.

1. Informational responses (1xx):

These codes indicate that the recipient server has received the request and is processing it. Examples include “100 – Trying” and “180 – Ringing.”

2. Success responses (2xx):

Success codes indicate that the request was successfully processed, and the desired action has been completed. Examples include “200 – OK” and “202 – Accepted.”

3. Redirection responses (3xx):

Redirection codes indicate that further action is needed to complete the request. The user agent may need to take additional steps to reach the desired endpoint. Examples include “301 – Moved Permanently” and “302 – Moved Temporarily.”

4. Client Error responses (4xx):

Client error codes indicate that there was an issue with the request, usually due to a mistake made by the user agent or client. Examples include “400 – Bad Request” and “404 – Not Found.”

5. Server Error responses (5xx):

Server error codes indicate that there was an issue on the recipient server’s end. These codes denote that the server encountered an unexpected condition or error while processing the request. Examples include “500 – Server Internal Error” and “503 – Service Unavailable.”

6. Global Failure responses

The 6xx response codes indicate that the response will fail, irrespective of the location where it’s tried. Examples include “604 – Does Not Exist Anywhere” and “607 – Unwanted”.

Why do SIP codes matter?

SIP response codes play a crucial role in troubleshooting and identifying the status of a communication session. By understanding these codes, businesses can proactively address issues, ensure smoother call operations, and provide a better experience for their customers.

Moreover, the insights gained from analyzing SIP response codes can help service providers optimize their systems, identify performance bottlenecks, and improve call routing strategies. These codes provide invaluable diagnostic information that can be used to enhance the overall quality and reliability of communication services.

A list of all SIP codes

Need to make a quick check of what a 3-digit SIP Response Code means? We’ve got you. Refer to the table below:

1xx = Informational SIP responses

SIP Response Code	SIP Equivalent	Description
100	Trying	Extended search is being performed so a forking proxy must send a 100 Trying response.
180	Ringing	The Destination User Agent has received the INVITE message and is alerting the user of call.
181	Call is being forwarded	Optional, send by Server to indicate a call is being forwarded.
182	Queued	Destination was temporarily unavailable, the server has queued the call until the destination is available.
183	Session progress	This response may be used to send extra information for a call which is still being set up.
199	Early dialog terminated	Send by the User Agent Server to indicate that an early dialogue has been terminated.

2xx = Success responses

SIP Response Code	SIP Equivalent	Description
200	OK	Shows that the request was successful.
202	Accepted	Indicates that the request has been accepted for processing, mainly used for referrals.
204	No notification	Indicates that the request was successful but no response will be received.

3xx = Redirection responses

SIP Response Code	SIP Equivalent	Description
300	Multiple choices	The address resolved to one of several options for the user or client to choose between.
301	Moved permanently	The original Request URI is no longer valid, the new address is given in the Contact header.
302	Moved temporarily	The client should try at the address in the Contact field.
305	Use proxy	The Contact field details a proxy that must be used to access the requested destination.
380	Alternative service	The call failed, but alternatives are detailed in the message body.

4xx = Request failures

Some of the most common 4xx SIP codes are below. See the complete list in the appendix.

SIP Response Code	SIP Equivalent	Description
400	Bad Request	The request could not be understood due to malformed syntax.
401	Unauthorized	The request requires user authentication. This response is issued by a UAS or a registrar.
404	Not found	The server has definitive information that the user does not exist at the (User not found)
407	Proxy authentication required	The request requires user authentication.
408	Request timeout	Couldn’t find the user in time.
409	Conflict	User already registered (deprecated).
411	Length required	The server will not accept the request without a valid content length (deprecated).
412	Conditional request failed	The given precondition has not been met.
415	Unsupported media type	Request body is in a non-supported format.
424	Bad location information	The request’s location content was malformed or otherwise unsatisfactory.
436	Identity info	The request has an Identity-Info header and the URI scheme contained cannot be de-referenced.
470	Consent needed	The source of the request did not have the permission of the recipient to make such a request.
480	Temporarily unavailable	Callee currently unavailable.
489	Bad event	The server did not understand an event package specified in an Event header field.

5xx = Server errors

SIP Response Code	SIP Equivalent	Description
500	Server internal error	The server could not fulfill the request due to some unexpected condition.
501	Not implemented	The SIP request method is not implemented here.
502	Bad gateway	The server, received an invalid response from a downstream server while trying to fulfill a request.
503	Service unavailable	The server is in maintenance or is temporarily overloaded and cannot process the request.
504	Server time-out	The server tried to access another server while trying to process a request, no timely response.
505	Version not supported	The SIP protocol version in the request is not supported by the server.
513	Message too large	The request message length is longer than the server can process.
555	Push notification service not supported	The server does not support the push notification service specified in the pn-provider SIP URI parameter.
580	Precondition failure	The server is unable or unwilling to meet some constraints specified in the offer.

6xx = Global failures

SIP Response Code	SIP Equivalent	Description
600	Busy everywhere	All possible destinations are busy.
603	Decline	Destination cannot/doesn’t wish to participate in the call, no alternative destinations.
604	Does not exist anywhere	The server has authoritative information that the requested user does not exist anywhere.
606	Not acceptable	The server has authoritative information that the requested user does not exist anywhere.
607	Unwanted	The called party did not want his call from the calling party. Future attempts from the calling party are likely to be similarly rejected.
608	Rejected	An intermediary machine or process rejected the call attempt.

Appendix: Full list of 4xx SIP codes

SIP Response Code	SIP Equivalent	Description
400	Bad Request	The request could not be understood due to malformed syntax.
401	Unauthorized	The request requires user authentication. This response is issued by UASs and registrars.
402	Payment required	Reserved for future use.
403	Forbidden	The server understood the request, but is refusing to fulfill it.
404	Not found	The server has definitive information that the user does not exist at the (User not found)
405	Method not allowed	The method specified in the Request-Line is understood, but not allowed.
406	Not acceptable	The resource is only capable of generating responses with unacceptable content.
407	Proxy authentication required	The request requires user authentication.
408	Request timeout	Couldn’t find the user in time.
409	Conflict	User already registered (deprecated).
410	Gone	The user existed once but is not available here anymore.
411	Length required	The server will not accept the request without a valid content length (deprecated).
412	Conditional request failed	The given precondition has not been met.
413	Request entity too large	Request body too large.
414	Request URI too long	Server refuses to service the request, the Req-URI is longer than the server can interpret.
415	Unsupported media type	Request body is in a non-supported format.
416	Unsupported URI scheme	Request-URI is unknown to the server.
417	Unknown Resource-Priority	There was a resource-priority option tag, but no Resource-Priority header.
420	Bad extension	Bad SIP Protocol Extension used, not understood by the server.
421	Extension required	The server needs a specific extension not listed in the Supported header.
422	Session interval too small	The request contains a Session-Expires header field with a duration below the minimum.
423	Interval too brief	Expiration time of the resource is too short.
424	Bad location information	The request’s location content was malformed or otherwise unsatisfactory.
428	Use identity header	The server policy requires an Identity header, and one has not been provided.
429	Provide referrer identity	The server did not receive a valid Referred-By token on the request.
430	Flow failed	A specific flow to a user agent has failed, although other flows may succeed.
433	Anonymity disallowed	The request has been rejected because it was anonymous.
436	Identity info	The request has an Identity-Info header and the URI scheme contained cannot be de-referenced.
437	Unsupported certificate	The server was unable to validate a certificate for the domain that signed the request.
438	Invalid identity header	Server obtained a valid certificate used to sign a request, was unable to verify the signature.
439	First hop lacks outbound support	The first outbound proxy doesn’t support the “outbound” feature.
440	Max-Breadth Exceeded	If a SIP proxy determined a response context had insufficient Incoming Max-Breadth to carry out a desired parallel fork, and the proxy is unwilling/unable to compensate by forking serially or sending a redirect, that proxy MUST return a 440 response. A client receiving a 440 response can infer that its request did not reach all possible destinations.
469	Bad info package	If a SIP UA receives an INFO request associated with an Info Package that the UA has not indicated willingness to receive, the UA MUST send a 469 response, which contains a Recv-Info header field with Info Packages for which UA is willing to receive INFO requests.
470	Consent needed	The source of the request did not have the permission of the recipient to make such a request.
480	Temporarily unavailable	Callee currently unavailable.
481	Call/Transaction does not exist	Server received a request that does not match any dialogue or transaction.
482	Loop detected	Server has detected a loop.
483	Too many hops	Max-Forwards header has reached the value ‘0’.
484	Address incomplete	Request-URI incomplete.
485	Ambiguous	Request-URI is ambiguous.
486	Busy here	Callee is busy.
487	Request terminated	Request has terminated by bye or cancel.
488	Not acceptable here	Some aspects of the session description of the Request-URI are not acceptable.
489	Bad event	The server did not understand an event package specified in an Event header field.
491	Request pending	Server has some pending request from the same dialogue.
493	Undecipherable	Request contains an encrypted MIME body, which recipient can not decrypt.
494	Security agreement required	The server has received a request that requires a negotiated security mechanism.

Speaking of SIP

SIP response codes are the language of communication systems, enabling efficient and effective call management. By familiarizing yourself with these codes, you can gain deeper insights into the status of your communication sessions and troubleshoot any issues that may arise. Additionally, service providers can leverage SIP response codes to deliver reliable and high-quality communication experiences to their customers.