This writable value configures, in seconds, ATM signaling timer T399, which starts when an ADD PARTY message is sent in the Add Party Initiated state and is normally stopped by ADD PARTY ACK, ADD PARTY REJ, or RELEASE, clearing the party and returning to the NULL Party state at first expiry; its range and default (14s for UNI 3.0/3.1, 34s for UNI 4.0) depend on the signaling version. It lets an admin bound how long the switch waits for a response when adding a new party to a point-to-multipoint call before giving up on that addition. For example, an admin on a UNI 4.0 network would expect T399 to default to 34 seconds rather than the shorter UNI 3.x value.