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

5.5.6505 Version Not Supported

This response indicates that the request has been refused by the server because of the SIP version number of the request. The detailed semantics of this response have not yet been defined because there is only one version of SIP (version 2.0) currently implemented. When additional version numbers are implemented in the future, the mechanisms for dealing with multiple protocol versions will need to be detailed.

5.5.7513 Message Too Large

The 513 Message Too Large response is used by a UAS to indicate that the request size was too large for it to process.

5.5.8580 Preconditions Failure

The 580 Preconditions Failure response [17] is used to reject an SDP offer in which the required preconditions cannot be met.

5.6 Global Error

This response class indicates that the server knows that the request will fail wherever it is tried. As a result, the request should not be sent to other locations. Only a server that has definitive knowledge of the user identified by the Request-URI in every possible instance should send a global error class response. Otherwise, a client error class response should be sent. A Retry-After header field can be used to indicate when the request might be successful.

5.6.1600 Busy Everywhere

This response is the definitive version of the 486 Busy Here client error response. If there is a possibility that the call to the specified Request-URI could be answered in other locations, this response should not be sent.

5.6.2603 Decline

This response has the same effect as the 600 Busy Everywhere but does not give away any information about the call state of the server. This response could indicate the called party is busy, or simply does not want to accept the call.