SIP - 5xx: Server Failure Responses


This class response is used to indicate that the request cannot be processed because of an error with the server. The server failed to fulfil an apparently valid request. The response may contain a Retry-After header field. The request can be tried at other locations because there are no errors indicated in the request. Some of the important server failure responses are discussed below.

500 Server Internal Error

  • 500indicates that the server has experienced some kind of error that is preventing it from processing the request.

  • It is one kind of server failure that indicates the client to retry the request again at this server after several seconds.

501 Not Implemented

  • It indicates that the server is unable to process the request because it is not supported.

  • This response can be used to decline a request containing an unknown method.

502 Bad Gateway

  • This response is sent by a proxy that is acting as a gateway to another network.

  • It indicates some problem in the other network is preventing the request from being processed.

503 Service Unavailable

  • This response indicates that the requested service is temporarily unavailable at that time.

  • The request can be retried after a few seconds, or after the expiration of the Retry-After header field.

504 Gateway Timeout

  • This response comes when the request failed due to a timeout occurred in the other network to which the gateway connects.

  • It is a server error class response because the call is failing due to a failure of the server in accessing resources outside the SIP network.

505 Version Not Supported

  • The server denies a request when it comes with a different SIP version number. The denial is indicated in this message.

  • Currently SIP version 2.0 is the only version implemented.

513 Message Too Large

  • This response is used by a UAS to indicate that the request size was too large for it to process.

580 Preconditions Failure

  • This response is used to reject an SDP offer in which required preconditions cannot be met.