AT&T MERLIN LEGEND Communications System PBX System Planning Manual page 70

Trunks
See "System Numbering' in Chapter 2.
Each pool can have as many or as few trunks as you want, but a trunk can be in
only one pool. In addition, only direct-line consoles can have line buttons for
trunks that have been assigned to pools.
Each pool should contain trunks of the same type (basic, WATS, FX, tie)
because you cannot control which trunk is selected. Ground-start and loop-start
trunks of the same type can be mixed in the same pool. For example, basic
trunks (loop-start and ground-start) should be grouped together in one trunk
pool, WATS trunks (loop-start and ground-start) in another pool, and FX trunks
(loop-start and ground-start) in yet another pool.
Do not mix different bands of WATS or FX trunks to different cities or include
both inbound-only or outbound-only trunks within a pool. DID trunks and/or
trunks used for auxiliary equipment cannot be grouped in pools. If you plan to
assign Pool buttons on telephones, do not group dial-in tie trunks in pools.
In typical pooled systems, all the trunks (except those mentioned previously) are
grouped in pools except single special-purpose trunks and any basic trunks that
are needed as personal lines assigned to a button on a telephone.
Group the trunks for the main pool first. The main pool should contain the trunks
used most often. In most businesses the trunks used most often are the basic
trunks. If your system includes ground-start basic trunks, reassign them from the
dial 890 extension pool to the main pool.
Once you decide which trunks are assigned to the main pool, decide how to
arrange the rest of the trunks in the remaining pools.
Decide whether to change the pool dial-out codes. The same considerations
apply as those used for reassigning station extension numbers.
Planning Form Instructions
Review PBX System Form 2c, System Numbering - Trunk Jacks,
determine which trunks to group into pools, and mark each pool on the PBX
System Form 3b, Outside Trunks - Pools.
1.
Write the factory-set pool dial-out code in the first column.
2.
To change the factory-set pool dial-out code:
Write the new number in the "Renumber To" column.
Locate PBX System Form 2d, System Numbering - Special
Renumbers and write the new number in the "Renumber To" column
of the "Pools" section of that form.
Transfer the information about all the trunks you plan to group into pool,
3.
from Form 2c to Form 3b:
Write the logical ID, trunk number, and trunk type in the columns.
Use the "Description" column to identify different bands (calling areas)
of WATS trunks and different destinations for FX trunks.
Trunk Options 3-15