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Signaling System No. 7 (SS7/C7): Protocol, Architecture, and Services by Jeff Hewett, Lee Dryburgh

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Appendix H. ISUP Timers for ANSI/ETSI/ITU-T Applications

This appendix lists all ISUP timers. The timer values are specified in ITU-T Q.764 [78]. ETSI ISUP timers [18] are identical to ITU-T timers.

Timers applicable to the US network are specified in ANSI T1.113-2000 [3].

Table H-1. ISUP Timers Specified in ANSI, ETSI and ITU-T

Timer

Duration Before Time-Out

Starts

Normal Termination

Action at Time-Out

min = minute(s)

sec = seconds(s)

ms = millisecond(s)

T1

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

T2

(ITU-T ONLY)

3 min

When controlling exchange receives Suspend (User) Message

Upon receipt of Resume (User) Message, at controlling exchange

Initiate release ...

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