Prepared by:

Nikhil Kumar

Electronics & Communication Department

5th Semester

NRI Institute of Research & Technology

Bhopal

INTRODUCTION

Communicati

on

• The process of conveying information from one place to another

Component

s

• Source of information• Transmitter• Receiver• Destination• Transmission medium

Telecommunication• A long distance communications• ‘tele’ Greek word for distant or

afar

Telephone• One of the most remarkable

devices ever invented

The Subscriber Loop

POTS – Plain Old Telephone Service

Simplest and most straightforward form of telephone service

Involves subscribers accessing the PTN through a pair of wires called the local subscriber loop (or simply local loop)

The Subscriber LoopLocal Loop

• Most fundamental component of a telephone circuit• Unshielded twisted pair(UTP) transmission line• Cable pair – 2 insulated conductors twisted together

Provides the means to connect telephone set of the subscriber’s location to the closest telephone office

A telephone office – end office/local exchange/central office

Standard Telephone Set

Basic telephone set

•Simple analog transceiver designed for converting speech of acoustical signals to electrical signals•Added features: multiple line selection, hold, caller ID

Standard Telephone Set

Butterstamp telephone(1878)• First telephone set that combined a transmitter

and receiver into single handheld unit

Rotary Dial Telephone• Introduced by western electric company also

called the bell system

Touch-Tone Telephone

Essential Components

Ringer Circuit

•Electronic oscillator•To alert the destination party of the incoming callsOn/Off

Hook Circuit

•Simple single throw-double-pole STDP switch

•Placed across the ‘tip’ and ‘ring’

•On hook (idle, open switch), off-hook (in use, closed switch)

Essential Components

Equalizer circuit•Combination of passive components (resistors & capacitors)

•To regulate the amplitude & frequency response of the voice signals

Speaker/receiver•Converts electrical signals received from the local loop to acoustical signals (sound waves)

•Enclosed in the handset of the telephone along with a microphone

Essential Components

•Transmitter•Converts acoustical signals in the form of sound pressure waves from the caller to electrical signals

Microphone

•Hybrid coil/duplex coil•Special balanced transformer used to convert 2-wire (local loop) circuit into 4-wire (telephone set) circuit•Outgoing signal –1 to 2V, incoming – half of outgoing signal

Hybrid network

•Enables the subscriber to output signals representing digits•Rotary dialer/Electronic dial pulsing circuit/touch tone keypad

Dialing circuit

Basic telephone call procedures

Step 1: Calling station goes off hook

Step 2: Switching machine returns an audible dial tone to the calling

station

Step 3: Caller dials the destination #

Step 4: Switching machine removes the dial tone from the

loop

Step 5: Switch interprets the # and locates the local loop for the

destination #

Basic telephone call procedures

•If off hook, busy signal sends to the calling station•If on hook, ringing signal and ring back signal will be sent

Step 6: Switch check the destination for the DC

current

Step 7: When destination answers the call, it completes the loop causing DC current to flow.

Step 8: Removes the ringing and ring back

signal

Step 9: When either end goes on hook

Call Progress Tones & Signals

Signaling

Categories of Signaling

Alerting signals

Indicate request for service

Ex. Going off hook, ringing

the destination

Supervising signals

Provide call status information

Ex. Busy, ring back signal

Controlling signals

Provide information in the form of

announcement

Ex. Change of number, number

no longer in service

Addressing signals

Provide routing information (calling & called numbers)

Dial tone

Dual tone multifrequency tones

Multifrequency tones

Dial pulses

Station busy – slow busy

Equipment busy - fast busy• Congestion tone

Ringing

Ring back

Receiver on hook

Receiver off hook

Essential Call Progress signals

DTMF Keypad Frequencies

DTMF Keypad Frequencies

700 + 900 1

700 + 1100 2

700 + 1300 3

700 + 1500 4

900 + 1100 5

900 + 1300 6

900 + 1500 7

1100 + 1300 8

1100 + 1500 9

1100 + 1700 Key pulse (KP)

1300 + 1500 0

1500 + 1700 Start (ST)

2600 IDLE

THANKS