AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 210

Applications
Mode Differences
The system must be configured for Behind Switch mode for full Centrex
operation.
For limited Centrex operation, if Centrex features are dominant, the system
should be configured for Behind Switch mode; if system features are dominant,
the system should be configured for Key or Hybrid/PBX mode.
The system can be used as a Hybrid/PBX behind a host switch by combining
the features of a Behind Switch system with the ground-start capabilities of a
Hybrid/PBX system. If a ground-start line is connected directly to the control
unit, the FCC considers the system a Hybrid. Any Behind Switch system with
full or limited Centrex service using a ground-start line must be registered as a
PBX system even if it operates in the Key mode.
Considerations and Constraints
With full Centrex service, during periods of high traffic, users may
experience delays in obtaining dial tone from the host. Should a user
begin dialing too rapidly, the first and second digits could be lost and the
call would be misdialed. This situation is more probable when the host is
another PBX, not a CO Centrex. With full Centrex service, the delay in
dial tone could cause misdialing when using System Speed Dialing or
Personal Speed Dialing.
With full Centrex service, dependence on loop-start lines during a high-
traffic period can cause a glare condition when calls grab the same line
simultaneously. The loop-start lines normally used in Centrex service do
not protect against glare.
With full Centrex service, some Centrex features require 2-or 3-digit
codes for access. These must be obtained from the telephone company
and provided to the customer at installation.
With full Centrex service, loop-start lines have higher cable losses than
ground-start lines and cannot assure secure toll restrictions.
With full Centrex service, single-line telephones have limited functionality
when connected directly to the CO Centrex host. They cannot access
system features or make inside calls. The can, however, use all of the
Centrex features via code numbers.
If the single-line telephone has the idle line preference programmed for
in intercom ring line, it cannot be used for internal conference, transfer,
or drop because it would result in a Centrex dial tone.
With limited Centrex service, touching a hard feature button to call a local
feature will cause misdialed calls.
If the limited Centrex configuration is programmed for Hybrid/PBX mode,
the use of calling groups, Shared System Access buttons, pools, and
other features is possible, and applications such as MERLIN MAIL, CAS,
and CMS can be used. If the mode is Behind Switch, the applications
cannot be used.
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Centrex Operation