Nortel RLC Installation And Administration Manual page 52

RLC description
An idle connection exists when no voice connections (voice paths) remain
open and when no data paths exist. Users at the remote site create data
paths when they press keys on their digital telephones. Signaling passing
from the host PBX to the digital telephone also creates data paths.
If anyone at the remote site places another call within 60 seconds, the RLC
resets the idle timer and uses the existing PSTN connection for the new
call. This eliminates the need to open a new PSTN connection and incur
unnecessary long distance charges. (Refer to Example 2 on page 26.)
The minimum call duration and idle timers work together to control PSTN long
distance charges. The following examples describe what happens when the
minimum call duration timer is set to 59 seconds and the idle timer is set to 60
seconds.
Example 1
After a 20-second call, the minimum call duration timer still has 39 seconds
remaining. If no one else at the remote site places a call, the RLC drops the
PSTN connection when the timer reaches 59 seconds. In this example, the
minimum call duration timer expires before the RLC initiates the idle timer.
After the minimum call timer, PSTN signaling with no digital telephone
activity keeps the primary PSTN connection up for no longer than two idle
timers.
Every PSTN connection remains active for at least the length of the
minimum call timer.
Additional trunks and circuit-only trunks active longer than the minimum
call timer remain active for an additional idle timer duration. This is the
case only if no additional bandwidth requests come to the host PBX.
Example 2
After a 65-second call, the idle timer starts. If no one at the remote site places a
call during the next 60 seconds, the RLC drops the PSTN connection. Since the
PSTN call exceeds 59 seconds, the minimum call duration timer expires before
activity ceased. At the conclusion of the call, the RLC initiates the idle timer to
prevent unnecessary charges.
26 RLC Installation and Administration Guide
Standard 4.0