Timers applicable to the US network are specified in ANSI T1.113-2000 .
Table H-1. ISUP Timers Specified in ANSI, ETSI and ITU-T
Duration Before Time-Out
Action at Time-Out
min = minute(s)
sec = seconds(s)
ms = millisecond(s)
15–60 sec (ITU)
4–15 sec (ANSI)
When Release Message is sent
Upon receipt of Release Complete Message
Retransmit Release Message and start timer T1
When controlling exchange receives Suspend (User) Message
Upon receipt of Resume (User) Message, at controlling exchange
Initiate release ...