AT&T MERLIN LEGEND Release 4.0 Feature Reference page 400

Feature Reference
When the system is set up and the Hybrid/PBX mode of operation is selected,
the system automatically groups trunks into the following pools:
All loop-start trunks (basic and special-purpose) are assigned to the main
pool. The factory-set extension number for the main pool is 70.
All ground-start trunks are assigned to the pool with the factory-set
extension number 890.
NOTES:
1. On initialization of a Release 1.0 system, all loop-start and ground-start trunk
programming reverts to loop-start. The ground-start pool never has trunks
assigned to it automatically but must be programmed after the ground-start
jacks are designated. In Release 1.1 and 2.0 (or later), ground-start trunks
are assigned to the ground-start pool on initialization, except in a system
modified for permanent Key mode operation.
All dial-in tie trunks are assigned to the pool with the factory-set extension
number 891.
All automatic-in tie trunks are assigned to the pool with the factory-set
extension number of 892.
2. The factory setting for the type of trunk connected to a 400 LS, 800 GS/LS,
408 GS/LS, 408 GS/LS-MLX, or 800 GS/LS-ID module is loop-start. The
system does not automatically make pool assignments for loop-start,
ground-start, or tie trunks that are emulated by using a T1 facility. Each of
these types must be grouped into a pool through system programming.
The system can have a maximum of 11 pools. Each pool can be assigned to a
button on a maximum of 64 telephones. The number of trunks in each pool is
limited only by the number of trunks connected to the system. However, a trunk
can be assigned to only one pool.
Considerations and Constraints
The maximum number of Pool buttons that can be assigned to multiline
telephones excluding Queued Call Consoles (QCCs) is limited only by the
maximum number of pools allowed (11) and the number of buttons on the
telephone.
The number of trunks in each pool is limited only by the number of trunks
connected to the system. A trunk can be assigned to only one pool.
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Pools