AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 42

Introduction
The Key mode of operation accommodates the following kinds of outside trunks:
Loop-start trunks, including basic lines, WATS, and foreign exchange
(FX)
Ground-start trunks (only if registered as MF and if not strapped for Key
mode, as described below) and emulated ground-start trunks on T1
facilities
DS1 facilities
Tie trunks and emulated tie trunks on T1 facilities
A standard Key system's trunks are all loop-start. A loop-start trunk introduces
a slight delay between the time the telephone company's CO recognizes a call
attempt and the time the call is processed. This delay is minimal and virtually
unnoticeable. Most residence and small business telephones have loop-start
trunks.
The communications system is configured for Key mode operation by system
programming, depending on how the system is registered with the Federal
Communications Commission (FCC), as described later in this section. If the
system is modified for Key-only operation by the hardware strap in the
processor module, no ground-start trunks can be connected to it. However,
ground-start emulation on a T1 facility is allowed.
NOTE:
The default programmed mode is Key.
On initialization of a Release 1.0 system, all loop-start and ground-
start trunk programming reverts to loop-start. In Releases 1.1
and 2.0, if the system is programmed for Key mode, the strap is
checked on initialization. If the strap is in (Key-only operation), all
trunks revert to loop-start. If the strap is not in, any programmed
designation of ground-start trunks is retained.
The following features are not available in Key mode:
Direct inward dialing (DID) trunks
Trunk pools
Automatic Route Selection (ARS)
QCCs and associated features
System Access buttons
Modes of Operation
1-14