AT&T MERLIN LEGEND Release 2.0 Equipment And Operations Manual page 79

Hardware Components
Different line/trunk modules support different types of telephone company
trunks. The types of trunks include the following:
Loop-start trunks— (incoming and outgoing calls) the simplest and most
common facilities in the nation-wide telephone network. They provide
incoming and outgoing calls and are intended primarily for single-line
telephones and older private branch exchanges (PBXS). A potential
problem of loop-start trunks is glare, that is, picking up the telephone to
make a call and another caller on an incoming call is already on the line.
Glare occurs because of delays in the telephone company's ringing
cycles and disconnects. This is normally not a problem for a residential,
single-line telephone, but can be more serious and complex with an
automated PBX.
Ground-start trunks—(incoming and outgoing calls) specifically
introduced to solve the problems that PBXs encounter on Imp-start
trunks, They provide an immediate signal when the trunk is seized and
when the call is completed and disconnected. Ground-start trunks can
be used only if registered with the FCC. Depending on the mode of
operation and the hardware strap in the processor module, the
registration number (provided by the account representative or
authorized dealer) includes the letters KF, MF, or PF. See FCC
Registration in Chapter 1 for details.
Tie trunks- a private line that directly connects two communications
systems. Thus, a caller on one system can call an extension on another
system by dialing an access code and the extension number. In more
complex tie trunk configurations, a user can access a facility on the other
system that does not exist on their own system.
Direct Inward Dialing (DID) trunks--- (incoming calls only) provide fast
access to specific individuals, that is, incoming calls can be routed
directly to the called extension, a calling group, or an outgoing trunk
without system operator assistance, These trunks are reliable and
efficient, but are more complex than loop-start or ground-start trunks.
Therefore, their installation and maintenance must be coordinated with
the telephone company,
DS1 connectivity programmed for either T1 or Primary Rate Interface
(PRI) operation-( incoming and outgoing calls) provides two-way
connection and high speed transmission of analog and digital signals
simultaneously. One trunk provides 24 channels; services provided on
the channels can be assigned and subsequently changed by you
instead of the telephone company, T1 operation enables the system to
transmit and receive voice and analog information; PRI enables the
system to transmit and receive voice, analog, and digital data, PRI
provides a wide range of benefits not available on any other single type
of trunk; for example, access to services on the channels can be on a
call-by-call basis, with the system selecting the most efficient or cost-
effective channel for that call.
The system supports 14 types of line/trunk and station modules. Figure 2-4
shows the line/trunk and station modules. Table 2-1 lists the type and number
Control Unit 2-5