Time starts when a trunk begins talking with another trunk (for example : trunk-
to-trunk transfer, outgoing from trunk, Tandem Trunking).
When this time expires, a warning tone is heard.
If Program 24-02-10 is set, the conversation disconnects after time expires.
This time is set again when the external digit timer expires.
One of the trunks used must be an analog trunk (or leased line).