AT&T MERLIN LEGEND Release 4.0 Feature Reference page 437

Feature Reference
Behind Switch mode
T1 data lines are not supported in Behind Switch mode.
Considerations and Constraints
General
If a B-channel is not available when a call is placed, a fast busy tone is
returned. While the tone is in progress, the line is considered busy. If the
originator goes on hook while the tone continues, the call is ended and the line
is idled. Otherwise, the call appearance is removed and the line is idled 15
seconds after the tone is applied.
A telephone is considered busy when: no SA button (aside from Originate Only
buttons) is available; Do Not Disturb is activated, or the extension is either being
programmed, is in forced idle; the alarm clock is being set. The caller hears a
busy tone; the call receives coverage if programmed.
A PRI line can be assigned to only one B-channel group.
If the internal dial plan uses extension numbers with different numbers of digits,
for example, both 3-digit extension numbers and 4-digit extension numbers,
Station Identification/Automatic Number Identification (SID-ANI) may not work
properly.
The PRI telephone number assigned to each channel must be different from the
numbers assigned to other channels assigned to the same B-channel group
and from that of the associated test number. Also, the number of each channel
must be the same number as that supplied by the PRI service provider. The test
telephone number assigned for each 100D (DS1) module in the control unit
must be different from the numbers assigned to other channels in the same
B-channel group and must be the same number as that supplied by the PRI
service provider.
An invalid timer value entered in system programming results in that number
being truncated to the closest valid value. If, for example, 45 is entered for a
counter that ranges from 0 to 30 seconds, 4 is recorded.
Primary Rate Interface (PRI) and T1
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