HTTP Response Code Key

1xx—Informational Responses

• 100 Trying: extended search being performed may take a significant time so a forking proxy must send a 100 Trying response
• 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
• 204 No Notification [RFC5839]

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

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