List of Methods and Response codes

SIP is similar to HTTP in request response transaction model. Each transaction consists of a client request that invokes a particular method or function on the server and at least one response. SIP reuses most of the header fields, encoding rules and status codes of HTTP, providing a readable text-based format.

This blog lists the methods invoked by request and responses.

List of SIP Responses Methods:

Request name	Description	RFC
INVITE	Indicates a client is being invited to participate in a call session.	3261
ACK	Confirms that the client has received a final response to an INVITE request.	3261
BYE	Terminates a call and can be sent by either the caller or the callee.	3261
CANCEL	Cancels any pending request.	3261
OPTIONS	Queries the capabilities of servers.	3261
REGISTER	Registers the address listed in the To header field with a SIP server.	3261
PRACK	Provisional acknowledgement.	3262
SUBSCRIBE	Subscribes for an Event of Notification from the Notifier.	3265
NOTIFY	Notify the subscriber of a new Event.	3265
PUBLISH	publishes an event to the Server.	3903
INFO	Sends mid-session information that does not modify the session state.	2976
REFER	Asks recipient to issue SIP request (call transfer.)	3515
MESSAGE	Transports instant messages using SIP.	3428
UPDATE	Modifies the state of a session without changing the state of the dialog.	3311

1xx—Informational Responses

• 100 Trying

• 180 Ringing
• 181 Call Is Being Forwarded
• 182 Queued
• 183 Session Progress

2xx—Successful Responses

• 200 OK
• 202 accepted: It Indicates that the request has been understood but actually can't be processed

3xx—Redirection Responses

• 300 Multiple Choices
• 301 Moved Permanently
• 302 Moved Temporarily
• 305 Use Proxy
• 380 Alternative Service

4xx—Client Failure Responses

• 400 Bad Request
• 401 Unauthorized (Used only by registrars or user agents. Proxies should use proxy authorization 407)
• 402 Payment Required (Reserved for future use)
• 403 Forbidden
• 404 Not Found (User not found)
• 405 Method Not Allowed
• 406 Not Acceptable
• 407 Proxy Authentication Required
• 408 Request Timeout (Couldn't find the user in time)
• 409 Conflict
• 410 Gone (The user existed once, but is not available here any more.)
• 412 Conditional Request Failed
• 413 Request Entity Too Large
• 414 Request-URI Too Long
• 415 Unsupported Media Type
• 416 Unsupported URI Scheme
• 417 Unknown Resource-Priority
• 420 Bad Extension (Bad SIP Protocol Extension used, not understood by the server)
• 421 Extension Required
• 422 Session Interval Too Small
• 423 Interval Too Brief
• 424 Bad Location Information
• 428 Use Identity Header
• 429 Provide Referrer Identity
• 433 Anonymity Disallowed
• 436 Bad Identity-Info
• 437 Unsupported Certificate
• 438 Invalid Identity Header
• 480 Temporarily Unavailable
• 481 Call/Transaction Does Not Exist
• 482 Loop Detected
• 483 Too Many Hops
• 484 Address Incomplete
• 485 Ambiguous
• 486 Busy Here
• 487 Request Terminated
• 488 Not Acceptable Here
• 489 Bad Event
• 491 Request Pending
• 493 Undecipherable (Could not decrypt S/MIME body part)
• 494 Security Agreement Required

5xx—Server Failure Responses

• 500 Server Internal Error
• 501 Not Implemented: The SIP request method is not implemented here
• 502 Bad Gateway
• 503 Service Unavailable
• 504 Server Time-out
• 505 Version Not Supported: The server does not support this version of the SIP protocol
• 513 Message Too Large
• 580 Precondition Failure

6xx—Global Failure Responses

• 600 Busy Everywhere
• 603 Decline
• 604 Does Not Exist Anywhere
• 606 Not Acceptable