Learning Outcome
CLO1-> Describe clearly the basic principle of a telephone network using the block diagram and the characteristic of telephone switching system using the concept of circuit-switch exchange.
Introduction to Telephone Network
- Basic principle of telephone network.
- Public switching telephone network.
Basic principle of telephone network.
- Telephone and telephony system
- Subscriber loop.
- Tip & Ring
- Basic function of telephone set.
- Telephone set compenent.
Public switching telephone network.
- What is PSTN
- Function of PSTN
- Major component of telephone network.
- Function of exchange.
- Type important of exchange.
- Type of exchange.
- Telephony network architecture.
- Basic all procedures.
- Private branch exchange. (PBX)
TELEPHONY
* In the world "TELEPHONY" , TELE means at a distant end and to phone is to speak. Thus telephony means speaking to a distant end by using telephone.
TELEPHONE SYSTEMS
* Is principally line communication systems in which signal are transmitted on the line and received from the line.
TYPE OF TELEPHONE SYSTEM.
*Analog telephone system.
*Digital telephone systems.
*Cellular telephone systems.
ANALOG TELEPHONE SYSTEM
*The analog systems was the first telephone systems established worldwide.
*Currently, telephone systems in a lot of countries are still completely analog to telephony.
*Two physically conductors, forming telephone line
-run from the subscriber's premises to telephone exchange (the connection to called party is made by exchange)
*Then the caller has access, through telephone exchange.
DIGITAL TELEPHONE SYSTEM
*Most telephone calls today are really digital telephone calls.
*In digital telephone system, the two ends of the call are analog, and the middle section is digital.
-conversions from analog to digital (A/D), and back to analog (D/A)
-They are made in such a way that it is essentially impossible to determine that they were made at all.
SUBSCRIBER LOOP
*Also referred to as a LOCAL LOOP.
*Is the physical link or circuit that connect from the customer premises to the central office (local exchange)
local loop=subscriberloop.
ANALOG TELEPHONE SYSTEM
*The analog systems was the first telephone systems established worldwide.
*Currently, telephone systems in a lot of countries are still completely analog to telephony.
*Two physically conductors, forming telephone line
-run from the subscriber's premises to telephone exchange (the connection to called party is made by exchange)
*Then the caller has access, through telephone exchange.
DIGITAL TELEPHONE SYSTEM
*Most telephone calls today are really digital telephone calls.
*In digital telephone system, the two ends of the call are analog, and the middle section is digital.
-conversions from analog to digital (A/D), and back to analog (D/A)
-They are made in such a way that it is essentially impossible to determine that they were made at all.
SUBSCRIBER LOOP
*Also referred to as a LOCAL LOOP.
*Is the physical link or circuit that connect from the customer premises to the central office (local exchange)
local loop=subscriberloop.
*A basic telephone set requires only two wires (one pair) from the telephone company to operate.
*The pair of wires connecting a subscriber to the closest telephone office is called LOCAL LOOP.
*One wire on the local loop is callled the Tip and the other the Ring.
*-48V was selected to minimiza electrolytic corrosion on the loop wires.
*-48V is used for supervisory signalling and to provide talk battery for microphone in the telephone set.
Tip & Ring
*Tip
*Is the ground side,
*Usually a green wire in the home of a single party customer.
Ring
*Is the battery (negative) side of a phone circuit.
*carries -48V of DC voltage when in an "idle" or "on hook" state.
*Usually a RED wire in the home of a single party customer.
**more reading at: http://en.wikipedia.org/wiki/Tip_and_ring
Basic function of telephone set
*Notify the subscriber when there are an incoming call.
*Provide signal to telephone network
*Convert speech energy to electrical energy in both side.
*Send the telephone number destination over the local loop.
*Regulate the amplitude of a speech signal of the calling person output of the line.
*Ensure that a small amount of the transmit signal is feedback to the speaker.
*Provide an open circuit and closed circuit to local loop.
*Provide call process signal between local exchange and subscriber.
Ringer Circuit
*An electromagnetic bell.
*Placed directly across the tip and ring of the local loop.
*Purpose: to alert the destination party of incoming calls.
*Audible tone must be loud enough to be heard from a reasonable distance.
ON/OFF Hook Circuit
*Sometimes called a switch hook.
*A simple single-throw, double-pole (STDP)
switch placed across the tip and ring.
*Mechanically connected to the telephone handset.
*Telephone is in use (off hook), switch is closed.
Equalizer Circuit
*Combination of passive component.
*Used to regulate the amplitude and frequency response of the voice signal.
*Help solve an important transmission problem:
-interdependence of transmitting and receiving efficiencies .
-Wide range of transmitter current caused by a variety of local loop cables with different resistance.
Speaker
*The receiver of the telephone
*Convert electrical signal received from the local loop through the hybrid network.
*Typically enclosed in the handset of the telephone along with the microphone.
Microphone
*Transmitter
*Convert acoustical signal in the form of sound pressure wave to electrical signals.
*Connected to the local loop through the hybid network.
*Converts:-
-Acoustical energy-mechanical energy-electrical energy
Hybrid Network
*Special balanced transformer
*To convert a two-wire circuit into a four-wire circuit and vice versa
*Separated the transmitted signal from the received signals.
*To allow a small portion of the transmit signal to be returned to the receiver in the form of side tone
