The bandwidth of voice channel in telephone set

-In a telephone system, the bandwidth of a voice channel ranges is from 300Hz to 3400Hz.


-The bandwidth allocated for a single voice frequency transmission channel is usually 4kHz,including two guard band (0-300Hz) and (3400Hz-4000Hz) to prevent adjacent frequency interference and,allowing a sampling rate of 8kHz to be used as the basic of the pulse code modulation system used for the digital PSTN.

Connectivity of telephone network architecture

connectivity of telephone network architecture

   

  

   MAIN DISTRIBUTION FRAME (MDF)

- main cross connection point between the Outside Plant (OSP) cable pairs and the exchange.

- it provides a great flexibility for line testing functions as well as electrical protection. Used for line     terminations.

   MAN HOLE

- a jointing chamber / breakout point of cables which one man can get down to the man hole and can     do the repairs.

- called feeder cables (large bundles) of twisted pair cable (from 50- 3000 pairs) are then taken to the    underground and then trough manholes to a cabinet,where they are terminated again.

CABINET 

- termination between the underground cables are coming from the MDF and distribution point (DP)     side.

- consists of two sides called primary and secondary.

- primary side from MDF

secondary side from DP

DISTRIBUTION POINT (DP)

- termination point between cabinet and the subcriber.

- each DP contains 10 subcribers

- drop wire is connected to the subcriber premises through the discharger unit.

-purpose of discharger unit is to protect the telephone set of the subcriber from lightning damages.     This uses the fuses and arrestors.

OVERHEAD WIRE

- suspended above the ground using poles.

- wire extended from underground cable and suspended above the ground and connected to the               distribution point.

DROP WIRE

- an aboveground or underground line or wire which connects the terminal of a distribution cable to a    subcriber's premises.

- consits of a telephone wire ( 1 pair of copper wire).

UNDERGROUND CABLE

- consists one or more conductors covered with suitable insulation and surrounded by a protecting        cover.

- the conducter used in cable should be tinned stranded copper or aluminium of high conductuvity.

- the cable must have the proper thickness.  

Telephone Set Component in Telephony

TELEPHONE SET COMPONENT

•DTMF circuit and keypad
• tone ringer circuit
• microprocessor unit (MPU)
• speech network
• line voltage regulator circuit
• loop or line interface
• on/off hook circuit
• speaker and microphone


THE BLOCK DIAGRAM OF TELEPHONE

TIP and RING

Tip and Ring explanation in Chapter 1

Figure 1: tip and ring in telephony

Tip and Ring are telephony slang for the two wires which make up the electrical circuit used for telephone wiring. Tip is the nickname for the electrically positive wire and Ring is the nickname for the electrically negative wire.

Differences Between TIP And RING

Telephone Set Component(additional note)

Block Diagram Of Telephone Set

Telephone Set Component

- DTMF circuit and keypad

  DTMF (Dual Tone Multi Frequency) as the name suggest uses a combination of two sine wave      tones to represent a key.

keypad

- Tone ringer circuit

   The tone ringer drives a piezoelectric sound element that produces an electronic ring.

Ringer Circuit

- Microprocessor

  The MPU with RAM, control the function of the telephone such as number storage, speed dialing,    redialing, and auto dialing.

- Speech network
  Speech network is also called voice network or telephone hybrid which connect the microphone and  speaker to the telephone line.

Hybrid

- Line voltage regulator
  The line voltage regulator convert dc voltage receive from the local loop and convert to constant level dc supply

- Loop or Line Interface
  - A special connector on the cable, called an RJ-11 modular connector, plugs into the matching wall jack.
  - Also known as the wiring block, modular interface or telephone box.

- On/ off hook circuit
  When the handset is on hook, the hook switch is open, thereby isolating all the telephone circuitry    from the local loop.

- Speaker and microphone
- The speaker convert electrical signal received from the local loop to acoustical signal.
- The microphone convert acoustical signal in form of sound pressure wave to the electrical signal.

Microphone and Speaker

                                                          Telephone Set Component

Telephone Network For Local Exchange(additional note)

Main Distribution Frame ( MDF )

• The Main Distribution Frame is situated at the telephone exchange.
• It used to connect the customer ( phone user ) with the main switching system after passing through the cabinet.

Cabinet

The cabinet's functions

• 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.
• 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 .

Distribution Point(DP)

• The DP Box's function is to make maintenance work and underground cabling easier.
• 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 DP through man-holes.
• The underground cable will end at the telephone exchange.

The Basic Function Of Electronic Telephone

The Basic Function Of Electronic Telephone

1. It requests the use of the telepohone system when the handset is lifted.

2. It indicates thet the system is ready for use by receiving a tone, called dialing tone.

3. 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.

4. It indicates the state of the call in progress by receiving tones indicating the status (ringing, busy,    etc).

5. It indicates an incoming call to the called telephone by ringing bell pr other audible tones.

6. It changes speech of the calling party to electrical signals for transmission to a distant party through the system, It change electrical signal received from a distant party to speech for the called party.

7. It automatically adjusts for changes in the power supplied to it.

8. It signals the system that a call is finished when a caller "hang up" the handset.

9. It ensure that a small amount of the transmit signal is fed back to the speaker, enabling talkers to hear themselves speaking. This feedback signal is sometimes called sidetone or talkback.

10. A built in microprocessor in an electronic telephone permits automatics control of the telephone's function and provides features such as telephone number storage, automatic dialing and redialing.

Public Switched Telephone Network

Public Switched Telephone Network

- circuit-switched technology which consists of transmission path and nodes,

- The PSTN subscriber does not require any specific knowledge – just dial and answer.

-The subscriber of PSTN are interconnected only temporary through switches

Main Elements Of PSTN:

1.Subscriber Loop

2.Customer Premises Equipment(CPE)

3.Exchange

4.Transport System

5.Signalling System