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MERLIN LEGEND Communications System Release 6.0
System Manager’s Guide
555-660-118
Issue 1
February 1998
About the System
Page 2-14Incoming Trunks
2
The types of trunks are:
■ Loop-Start Lines (Incoming and Outgoing Calls). Provide incoming and
outgoing calls and are intended primarily for single-line telephones and
older PBXs. They are the simplest (often the least expensive) and most
common facilities in the nationwide telephone network. Although they are
not appropriate for some situations, they are necessary for others (for
example, some caller identification services).
■ Ground-Start Trunks (Incoming and Outgoing Calls). Provide a signal at
the beginning and end of incoming and outgoing calls to determine the
availability of a trunk before the CO routes an incoming call on it. Also,
when either the caller or the called party hangs up, the entire circuit is
disconnected and dropped. These trunks were introduced to solve the
problems that PBXs encounter on loop-start trunks (namely, glare and
unreliable disconnect), as described in the Introduction booklet.
■ Tie Trunks. Private lines that directly connect two communications
systems. Using a tie trunk, a user on one system can call an extension on
another system by dialing an access code and the extension number or
simply the extension number. In Release 6.0 and later systems
(Hybrid/PBX mode only), tandem tie trunks, either analog or T1-emulated,
can be used for networking. In this case, the user dials only the non-local
extension number without an access code. For more information, see the
Network Reference
.
In more complex tie trunk configurations, a person can tie into another
system and use a trunk that does not exist on his or her own system. For
example, in a company with locations in New York, Chicago, and Los
Angeles (with tie trunks between New York and Chicago, and Chicago and
Los Angeles), users in New York can access a Los Angeles trunk and
make a local call as if they were in Los Angeles themselves.
■ Direct Inward Dial (DID) Trunks (Incoming Calls Only). Provide fast
access to specific individuals; incoming DID calls can be routed directly to
an extension or calling group without system operator assistance.
■ Digital Facilities. MERLIN LEGEND supports two different types of digital
facilities: Digital Signal 1 (DS1) and, in Release 4.0 and later systems,
National Integrated Services Digital Network 1 Basic Rate Interface
(abbreviated
NI-1 BRI
) facilities. T1, PRI, and BRI are the system’s
interfaces to these Integrated Services Digital Network (ISDN) facilities,
which provide end-to-end digital connectivity and switched connections to
other networks. All three interfaces allow high-speed data transfer.
— National Integrated Services Digital Network 1 Basic Rate Interface
(Incoming and Outgoing Calls). One NI-1 BRI facility carries the
equivalent of three “lines.” Two are called
B-channels
and provide voice
and data communications services. A third D-channel controls signaling
and maintains operations on the B-channels.