is to carry application level information along the SIP signaling path. The INFO method is not used to change the state of SIP calls, or the parameters of the sessions SIP initiates. It merely sends optional application layer information, generally related to the session. It is necessary that the mid-session signaling information traverse the post session setup SIP signaling path. This is the path taken by SIP re-INVITEs, BYEs and other SIP requests that are tied to an individual session. This allows SIP proxy servers to receive, and potentially act on, the mid-session signaling information. This document proposes an extension to SIP by defining the new INFO method. The INFO method would be used for the carrying of mid-call signaling information along the session signaling path. 1.1 Example Uses The following are a few of the potential uses of the INFO message: - Carrying mid-call PSTN signaling messages between PSTN gateways, Carrying DTMF digits generated during a SIP session. - Carrying wireless signal strength information in support of wireless mobility applications. - Carrying account balance information. Donovan Standards Track [Page 2] RFC 2976 SIP INFO Method October 2000 - Carrying images or other non streaming information between the participants of a session. These are just potential uses; this document does not specify such uses nor does it necessarily recommend them. It can also be envisioned that there will be other telephony and non-telephony uses of the INFO method. 2. INFO Method The INFO method is used for communicating mid-session signaling information along the signaling path for the call. The INFO method is not used to change the state of SIP calls, nor does it change the state of sessions initiated by SIP. Rather, it provides additional optional information which can further enhance the application using SIP. The signaling path for the INFO method is the signaling path established as a result of the call setup. This can be either direct signaling between the calling and called user agents or