Switching Equipment - Lucent Technologies MERLIN LEGEND Release 6.1 System Manager's Manual

MERLIN LEGEND Communications System Release 6.1
System Manager's Guide 555-661-118
B About Telecommunications

Switching Equipment

facility is programmed for (T1 or PRI). If programmed for T1 service, the channels
can be configured to emulate different types of trunks (loop-start, ground-start,
DID, and tie) according to business needs, and can provide a variety of special
services. If programmed for PRI service, additional special services are available
and each B-channel can be programmed to dynamically provide different services
over the same B-channel.
Switching Equipment
The primary function of switching equipment is to interconnect the transmission
facilities at various key locations and route the telephone signals through the
telephone network. The telephone network is composed of a number of these key
centralized locations called central offices (COs). At the COs, the electrical signal
carried on one telephone circuit is connected, or switched, to another circuit,
forming a communications path; that is, the caller's line is connected to the called
party's line so they can hold a conversation.
In the early telephone network, switching was performed manually by human
operators. Today, electronic computer-controlled switching systems are fast,
flexible, and economical, providing reliable, efficient, and cost-effective service.
There are now also private switches that, rather than being located at the
telephone company's CO, are located on a company's premises. These systems,
called private branch exchanges (PBXs), were developed because most of a
business' calls are between telephones on-site within the company. The MERLIN
LEGEND Communications System is a such a switch, located on the customer's
premises, that provides advanced services and features and yet also provides
many of the special functions originally performed by human operators.
The Evolution of Switches
The method, type, capabilities, and capacities of switches have evolved as
geographic areas expanded and technological advances became available.
Three basic types of technology have been used in switching:
Manually-Operated Switching. Human operators made the connections
of circuits by placing plug-ended wires into jacks on a switchboard. Manual
switching was slow, labor-intensive and, therefore, costly, but it afforded
some special functionality: calls could be forwarded, messages taken, and
calls interrupted.
Electromechanical Switching. Electrically operated devices with
mechanical parts and motion. Electromechanical switching automated the
manual labor and allowed telephone service to be universally affordable,
but the technology was inflexible since changes in service required
changes in the device itself. It also required high maintenance due to wear
and tear on parts, and did little more than switch calls.
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Issue 1
August 1998
Page B-5