INTRODUCTION TO

TELEPHONE NETWORK

Understand basic principle of telephone system.

Define telephony and telephony system.

Define subscriber loop.

Explain the subscriber loop by drawing a simplified

subscriber loop showing telephone set connected to

a local exchange.

Identify tip and ring.

Explain the basic functions of a standard telephone set.

Draw a block diagram of a telephone set components :

ringer circuit, on/off hook circuit, equalizer circuit, speaker,

microphone, hybrid network and dialing circuit.

Explain the function of each block.

Explain the bandwidth of a voice channel in a telephone

system.

Communication

Telecommunication

Tele/communications

- The process of transmitting a message between two remote locations.

- Message - could be Voice, Music, Textual, Pictorial (graph, diagram, image, etc.) or moving image (video).

The telephone network, until the last decade, was almost entirely analog

The telecommunication system is divided into four possible elements.

Telecommunication

End systems or instruments

Transmission Switching Signaling

There are 3 main parts as shown in above figure

Transmitting transducer

Receiving transducer

One pair wire system

Defination

Telephony is the field of technology involving the

development, application, and deployment of

telecommunication services for the purpose of electronic

transmission of voice, fax, or data, between distant parties.

Telephony system - A system of telecommunications in which

telephonic equipment is employed in the transmission of

speech or other sound between points, with or without the use

of wires.

The telephone network is made of 5 major components :

End Instrument (Telephone)

Local Loop

Exchange

Trunk

Transmission Media

Figure : Major components in telephone network

TELEPHONE SYSTEM

The telephone is a familiar end instrument in

telecommunication switching system.

The development of telephone and circuits started around

1850. The table below shows the development of

telephone.

Main Distribution Frame (MDF)

The Main Distribution Frame is situated at the telephone exchange. It is used to

connect the customer (phone user) with the main switching system after

passing through the cabinet. It comprises of all the customers and data which

are situated in one area or district.

The duties of MDF :

To test the phone line.

To execute the jumper process.

To check the problem phone line.

To cut the phone line manually.

To connect the phone line manually

Cabinet

The cabinet is a place to distribute lines to the DP Box before reaching a

customers house.

Connection from the cabinet to the main distributor normally uses the lead

cable of different sizes where each of it has 200 pairs and to be distributed to

about 20 DP Box.

From the cabinet to the DP Box, it uses the plastic cable. In the cabinet, there

are 1800 pairs of terminals.

The Cabinets functions are as follows :

To save the usage of cable and replacing cable would be easier.

To avoid the joint to be opened and this would save cost and time.

To act as a place to perform maintenance checking.

To upgrade the arrangement of lines.

Distribution Point Box (DP)

The DP Boxs function is to make maintenance work and underground cabling

easier.

Usually, the DP Box has 10 pairs but only 8 pairs are used and the others kept

for testing work from DP Box to the main distributor .

Upper Cable

The upper cable is used to make connection with the

customers using the DP Box. The two wire cable normally is

used.

Underground Cable

The underground cable is connected to the cabinet from the

DP through man-holes. The underground cable will end at

the telephone exchange

TIP RING

TIP is the ground side (positive)

RING is the battery (negative) side of phone circuit

TIP is The GREEN wire which is connected to the wall jack

RING is The RED wire which is connected to the wall jack

it used to provides the

ground return.

it function is to carry the

voice and ringing signal

Usually measures ground when on-hook

Usually measures -48Volts when on-hook

It requests the use of the telephone system when the

handset is lifted.

It indicates that the system is ready for use by

receiving a tone, called dialing tone.

It sends the number of the telephone to be called to

the system. This number is initiated by the caller

when the number is pressed or the dial is rotated.

It indicates the state of the call in progress by

receiving tones indicating the status (ringing, busy,

etc).

It indicates an incoming call to the called telephone

by ringing bells or other audible tones.

It changes speech of the calling party to electrical

signals for transmission to a distant party through the

system. It change electrical signals received from a

distant party to speech for the called party.

It automatically adjust for changes in the power

supplied it.

It signals the system that a call is finished when a

caller hang-up the handset.

A telephone set is an apparatus that creates an exact

likeness of sound waves with an electric current. The

essential components of a telephone set are the

ringer circuit, on/off hook circuit, equalizer circuit,

hybrid circuit, speaker, microphone, and a dialling

circuit.

Human speech covers the frequency range of 100 to

7000 Hz (hertz) but research has shown that the

intelligence part of human speech is carried in the

300 - 3400 Hz range. This range is called the Voice

Band.

The Voice Channel has a range of 0 to 4 kHz (4000

Hz). The area from 3400 to 4000 Hz is used for

system control and is called Out of Band Signalling.

35

Voice Channel

0-4,000 Hz

Frequency (Hertz)

Voice Bandwidth 300-3,300 Hz

Guard

Band

Guard

Band

0 300 3,300 4,000

Volt

age

Discuss with your partner, sketch the block diagram

of a telephone set.

Two Minute paper