AT&T MERLIN LEGEND Release 3.1 System Manager's Manual page 55

Incoming Trunks
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NOTE:
Facility is a general term that designates a communications path between a
telephone system and the telephone company central office. Technically, a
trunk connects a switch to a switch, for example, the MERLIN LEGEND
Communications System to the central office. Technically, a line is a loop-start
facility or a communications path that does not connect switches, for example,
an intercom line or a Centrex line. However, in actual usage, the terms line and
trunk are often applied interchangeably. In this guide, we use lines/trunks and
line/trunk to refer to facilities in general. Specifically, we refer to digital facilities .
We also use specific terms such as personal line , ground-start trunk , DID trunk ,
and so on. When you talk to your local telephone company central office, ask
them what terms they use for the specific facilities they connect to your system.
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About the System
T1 Data Operation. Available in Release 4.0 and later, T1 data
operation allows high-speed data communications over the public
switched network; this is called T1 Switched 56 service . It also
provides data tie "lines" to connect one MERLIN LEGEND
Communications System to another or to a DEFINITY system. A
T1 data-operation "line" is a B-channel.
Primary Rate Interface (PRI) Operation. The 24 "lines" include 23
B-channels. Each B-channel can dynamically provide voice and
data services; one D-channel carries signaling information for the
B-channels.