AT&T Labs Cisco Systems The IETF has completed its work on the core specification of TWAMP -- the Two-Way Active Measurement Protocol. This memo describes an OPTIONAL feature for TWAMP, that gives the controlling host the ability to start and stop one or more individual test sessions using Session Identifiers. The base capability of the TWAMP protocol requires all test sessions that were previously requested and accepted to start and stop at the same time. [STANDARDS-TRACK]