Incoming Trunks - AT&T MERLIN LEGEND Release 3.1 System Manager's Manual

Incoming Trunks

Incoming Trunks
Trunks are the telephone company's facilities, provided by the central office
(CO) to carry voice or data communications (see Figure 2–6). There are a
variety of trunks, each with different capabilities. These types have evolved over
the years as technology has advanced and customer needs have expanded.
The decision concerning the type of trunks chosen for your company's system
depends primarily on your company's needs. Other factors include cost (due to
differing capabilities, the use of some trunks is more expensive than others),
and availability (some of the advanced trunks are not available everywhere).
Your company chooses trunks before the system is installed. An AT&T
representative works with you or your company's representative to identify
needs and, therefore, the appropriate type and number of trunks. When the
AT&T representative places the order for the system equipment, she or he also
contacts the local telephone company and arranges for the trunks.
Depending on the trunk type and what the CO can provide, a variety of services
are available, for example, incoming and outgoing WATS (INWATS and
OUTWATS).
The types of trunks are:
Loop-Start Trunks (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). Provides 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.
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About the System