Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright © The Internet Society (2000). All Rights Reserved. Abstract This document proposes an extension to the Session Initiation Protocol (SIP). This extension adds the INFO method to the SIP protocol. The intent of the INFO method is to allow for the carrying of session related control information that is generated during a session. One example of such session control information is ISUP and ISDN signaling messages used to control telephony call services. This and other example uses of the INFO method may be standardized in the future. Table of Contents Introduction Example Uses INFO Method Header Field Support for INFO Method Responses to the INFO Request Method Message Body Inclusion Behavior of SIP User Agents Behavior of SIP Proxy and Redirect Servers 2.5.1 Proxy Server 2.5.2 Forking Proxy Server 2.5.3 Redirection Server INFO Message Bodies Guidelines for extensions making use of INFO Security Considerations References Copyright 2002 The McGraw-Hill Companies, Inc. Click Here for Terms of Use. Donovan Standards Track [Page 1] RFC 2976 SIP INFO Method October 2000 Acknowledgments Author's Address Full Copyright Statement 1. Introduction The SIP protocol described in [1] defines session control messages used during the setup and tear down stages of a SIP controlled session. In addition, the SIP re-INVITE can be used during a session to change the characteristics of the session. This is generally to change the properties of media flows related to the session or to update the SIP session timer. However, there is no general-purpose mechanism to carry session control information along the SIP signaling path during the session. The purpose of the INFO message 