Lucent Technologies 5 manual Switching Equipment, Evolution of Switches

MERLIN LEGEND Communications System Release 5.0		Issue 1
System Manager’s Guide 555-650-118		June 1997
B About Telecommunications
	Switching Equipment	Page B-5
	Switching Equipment	2

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 2

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.

■Electronic Switching. Electronic, computer-controlled equipment. Electronic switching reduced the size, power consumption, and cost. At the same time, it increased operating speeds, ruggedness, and reliability. Computer control provides flexibility because changes and enhancements are made to the switching system’s software rather than to the hardware.

Manual switching was used for the first few decades of telephone service.

Switching was performed by human operators who made the actual connections