Lucent Technologies 6 User Manual

Issue 1

February 1998

About the System 

Page 2-2

Background 

Many of the principles of telephone communications have not changed since 
Alexander Graham Bell made the first phone call in 1876. Because learning about 
these concepts helps explain how the system works, this chapter begins with 
some background information about telephone communications. For a more 
detailed history and description, see Appendix B, “About Telecommunications.”

If you are already familiar with the concepts described in this chapter, you can skip 
the chapter.

2

Alexander Graham Bell and his assistant, Thomas A. Watson, demonstrated the 
first working model of a telephone on March 10, 1876. Bell made the call from a 
transmitter in one room to a receiver a few rooms away.

The first telephone installations were set up like that first call, as direct 
connections between one telephone and another. When more and more 
telephones were installed, it quickly became impractical to have every phone 
connected directly to every other phone. Thus, the concept of 

switching 

developed, that is, all telephones connected physically to all other telephones, but 
each telephone could make the electrical cross-connection between itself and 
another phone so that the caller was connected to the called party. 

Again, as more and more telephones and lines were installed, it became 
impractical to have each telephone perform this switching function, so all lines 
from all phones were brought into a common place, called a 

central office (CO) 

or 

exchange

 (see 

) where human operators switched calls at 

switchboards. This 2-way connection between the telephone and the CO was 
(and still is) called the

 local loop. 

Eventually, more and more COs were created 

and interconnected, until the current global telephone network evolved (see 

As geographic areas expanded and the global telephone network evolved, and as 
technological advances became available, switches also evolved and are now 
fully automatic and controlled by computers. 

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

), made sense because most of a 

business’ calls are between telephones on site within the company.

The MERLIN LEGEND Communications System includes such a switch, located 
on a company’s premises, that offers access to even more powerful telephone 
network applications and services. It can operate as a PBX (

Hybrid/PBX mode

)

 

or 

can be set up to operate in one of two other modes that define how the system 
works. The system can also use state-of-the-art telephone equipment.