scope:

This document proposes an IANA Registration extension to the Session Initiation Protocol (SIP) Reason Header to be included in a BYE Method Request as a result of a session preemption event, either at a user agent (UA), or somewhere in the network involving a reservation-based protocol such as the Resource ReSerVation Protocol (RSVP) or Next Steps in Signaling (NSIS). This document does not attempt to address routers failing in the packet path; instead, it addresses a deliberate tear down of a flow between UAs, and informs the terminated UA(s) with an indication of what occurred.