"Session Timers in the Session Initiation Protocol (SIP)" - Christer Holmberg, Steve Donovan, Jonathan Rosenberg

2020-06-29, rev -03: This document defines an extension to the Session Initiation Protocol (SIP). This extension allows for a periodic refresh of SIP sessions through a re-INVITE or UPDATE request. The refresh allows both user agents and proxies to determine whether the SIP session is still active. The extension defines two new header fields: Session- Expires, which conveys the lifetime of the session, and Min-SE, which conveys the minimum allowed value for the session timer.