SIP Response Codes

  • Updated on Oct 23, 2025
  • Published on Oct 17, 2024
  • 2 minute(s) read
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Some SIP phones and all PBXs display errors or a prompt using the SIP Response codes. This page contains a list of SIP codes that can help you diagnose problems.

SIP Responses, class 1

The 1xx response codes are provisional messages sent indicating call progress.  

  • 100 Trying    

  • 180 Ringing    

  • 181 Call Is Being Forwarded    

  • 182 Queued    

  • 183 Session Progress    

SIP Responses, class 2

The 2xx class of response codes indicates success.  

  • 200 OK    

SIP Responses, class 3

The 3xx response codes indicate a redirection of the call.  

  • 300 Multiple Choices    

  • 301 Moved Permanently    

  • 302 Moved Temporarily    

  • 305 Use Proxy    

  • 380 Alternative Service    

SIP Responses, class 4

The 4xx response codes indicate request failures.

  • 400 Bad Request    

  • 401 Unauthorized: Used only by registrars. Proxies should use proxy authorization 407    

  • 402 Payment Required (Reserved for future use)    

  • 403 Forbidden    

  • 403 - Insufficient funds ( often related to the balance on the account or the Fraud control settings for the destination number)

  • 404 Not Found: User not found ( Typically the PBX will deliver when an inbound route is not setup for the DID)

  • 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 no longer available    

  • 413 Request Entity Too Large    

  • 414 Request-URI Too Long    

  • 415 Unsupported Media Type    

  • 416 Unsupported URI Scheme    

  • 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    

  • 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    

  • 491 Request Pending    

  • 493 Undecipherable: Could not decrypt S/MIME body part    

SIP Responses, class 5

The 5xx response codes indicate server failures.  

  • 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    

SIP Responses, class 6

The 6xxx response codes represent global failures.  

  • 600 Busy Everywhere    

  • 603 Decline    

  • 604 Does Not Exist Anywhere    

  • 606 Not Acceptable    

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