Telephone Networks

Telephone Networks:

Ø The earliest electronic network is the telephone system.

Ø This telephone network commonly uses analog technology that was quite different from digital technology used in the computer-based networks.

Ø Tele in Greek “at a Distance”.

Ø Telephone network adopt/uses circuit switching mechanism When two nodes communicate with each other over a dedicated communication path, it is called circuit switching.

Ø Switching means Selects and direct communication signals to specific user or group of users.

Ø The entire network, which is referred to as Plain Old Telephone System (POTS),was originally an analog system using analog signal to transmit voice.

Ø The telephone network transmits analog signals and hence a modem is required whenever a computer or terminal is connected to the telephone line. The modem then converts digital data from a computer to an analog signal that can be transmitted via a telecommunication line and converts the analog signal received to computer data.

Ø The telephone network is made up of three major components:

·       local loops

·       Trunks,

·       Switching offices.

Ø The telephone network has several levels of switching offices such end offices, tandem offices, and regional offices.

[ A telephone switching center (central office) that does not connect directly to the customer. It connects offices in the same network or between networks, but always deals with trunks rather than customer lines.]

A)     Local Loops:

Ø Local loop is a twisted-pair cable that connects the subscriber telephone to the nearest end office or local central office.

Ø The local loop, when used for voice, has a bandwidth of 4000Hz (4kHz).

Ø The telephone number is associated with each local loop.

Ø The first three digits of a local telephone number define the office, and the next four digits define the local loop number.

B)     Trunks:

Ø Trunks are transmission media that handle the communication between offices.

Ø A trunk normally handles hundreds or thousands of connections through multiplexing.

Ø Transmission is usually through optical fibers or satellite links.

C)      Switching Offices:

Ø To avoid having a permanent physical link between any two subscribers, the telephone company has switches located in a switching office.

Ø A switch connects several local loops or trunks and allows a connection between different subscribers.