ciated processing rules for the body, the body MAY be rendered and displayed to the user. The INFO is responded to with a 200 OK. If the INFO request contains a body that the server does not understand then, in the absence of INFO associated processing rules for the body, the server MUST respond with a 415 Unsupported Media Type message. Header Where Priority Proxy-Authenticate Proxy-Authorization Proxy-Require Require Retry-After Retry-After 404,480,486 Retry-After Retry-After 600,603 Response-Key Record-Route Record-Route Route Server Subject Timestamp gc(1) Unsupported User-Agent gc(2) Warning WWW-Authenticate401 Table 2 Summary of header fields, P-Z Bodies which imply a change in the SIP call state or the sessions initiated by SIP MUST NOT be sent in an INFO message. Other request failure (4xx), Server Failure (5xx) and Global Failure (6xx) responses MAY be sent for the INFO Request. Message Body Inclusion The INFO request MAY contain a message body. Donovan Standards Track [Page 5] RFC 2976 SIP INFO Method October 2000 2.4 Behavior of SIP User Agents Unless stated otherwise, the protocol rules for the INFO request governing the usage of tags, Route and Record-Route, retransmission and reliability, CSeq incrementing and message formatting follow those in [1] as defined for the BYE request. An INFO request MAY be cancelled. A UAS receiving a CANCEL for an INFO request SHOULD respond to the INFO with a "487 Request Cancelled" response if a final response has not been sent to the INFO and then behave as if the request were never received. However, the INFO message MUST NOT change the state of the SIP call, or the sessions initiated by SIP. 2.5 Behavior of SIP Proxy and Redirect Servers 2.5.1 Proxy Server Unless stated otherwise, the protocol rules for the INFO request at a proxy are identical to those for a BYE request as specified in [1]. 2.5.2 Forking Proxy Server Unless stated otherwise, the protocol rules for the INFO request at a proxy are identical to those for a BYE request as specified in [1]. 2.5.3 Redi