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Telephone

Functions

Signaling

Convert voice signals to electrical signals( which the CO switch canunderstand) and vice versa

Provides side tone at correct levels

Allows you to hear your own voice while your speaking

A hybrid circuit in the telephone couples a small portion of thetransmitters signal to the receiver

Provides Ring Current

70 90 VAC, 20Hz sent from the CO to the telephone

Mechanical ringers

Ring detect circuit

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Telephone

Functions

Provides Dial Tone and DTMF

Rotary dial caused interruptions to current flowing through the line

The switch counted the interruptions to interpret the digits

Dual Tone Multi-Frequency introduced by AT&T in 1964 Depressing the buttons causes a unique set of tones to be sent to the

switch

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Telephone

Components of the Telephone

Transmitter

Receiver

Hybrid

Dial or DTMF pad

Ringer

Hook switch

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TelephoneHow the Telephone Works

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TelephoneHow the Telephone Works

How the Telephone Works

The bell: is connected via the capacitor when the receiver is resting in itscradle (on hook). When a call is placed to the B-subscriber, the bell isenergized via the capacitor by an alternating voltage (approximately 90V, 25 Hz), producing a ringing signal that notifies the subscriber of the

incoming call. The Hook:When the A-subscriber lifts the receiver to place a call, the speech

circuit and keypad are connected (and the bell is disconnected) via the hookfunction. This alerts the local exchange that a number is about to be dialed: theB-subscriber number. When the B-subscriber lifts the receiver to answer, thehook switch disconnects the bell in his telephone and instead connects the speechcircuit and keypad.

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How the Telephone Works - DTMF

The Key Pad

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TelephoneHow the Telephone Works

How is Speech transmitted over

the phone?

Speech Circuit

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TelephoneHow the Telephone Works

How is Speech transmitted over the phone?

The Speech Circuit

The primary function of the speech circuit is to adapt the sound level of incoming voice,outgoing voice and side tone. The circuit comprises two amplifier blocks (one foramplifying the microphone current and one for feeding the receiver) and a bridge

connection that separates voice signals to be sent to the microphone and to the receiver

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TelephoneHow the Telephone Works

Receiver

The current generated by the incomingspeechpasses through an electromagnet that isconstructed around a permanent magnetand connected to a membrane. Theoscillations, or movement, of the membraneare converted db to sound waves that are

perceived by the ear.

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TelephoneHow the Telephone Works

Transmitter-Microphone

The old carbon microphones are being increasingly replacedby electret microphones. The material upon which these newmicrophones are based consists of a thin plastic film, similar toTeflon, that is exposed to a strong electrical field. The filmretains its negative and positive charges after the externalelectrical field is removed -somewhat analogous to the polesof a magnet. The Teflon film (electret material) is stretchedover a fixed electrode. The movable electrode consists of a

thin metallic layer covering the electret material. Irregularitiesin the surface of the fixed electrode cause a number of smallair gaps to arise between the electric and the fixed electrodeThe electrical field existing in each of the air gaps is generatedby the electret's charge. The movements of the membranechange the size of the air gaps and hence their capacitance.These capacitance variations result in voltage variations thatappearacross the load resistor, R.

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TelephoneHow the Telephone Works

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V5.1 vs V5.2

V5.2

consists of 1 to 16 E1 I/f

supports concentration, dynamictime slot assignment

Supports PSTN and ISDN BRI

&PRI protection for signaling and

control channels

Maximum 3 TS for signaling /control per link

LE AN

V5.1

Single E1 interface No concentration, fixed time

slot assignment

Supports PSTN and ISDN BRI

No protection

Maximum 3 TS for signaling /control

V5.1

LE AN

V5.2

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FUNCTIONS OF SUB ACCESS INTERFACE

BORSCHT

CONCENTRATION

A-D CONVERSION

EXTEND SIGNALS

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FGFFGF

EVOLUTION OF V 5.2

DGDG

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FGFFGF

Advantages of Deploying AN

Saving copper loopRemote subs can enjoy new tech

AN & LE are vendor independent.

Billing and CDR can be generated at localexchange

Central administration and databasemanangement

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DLC NETWORK DIAGRAMDLC NETWORK DIAGRAM

MDF

Primary

Cable

Joints

Cabinets

Secondary

cable

Pillar

Joints

Joints

DP

DP

Conventional Networks

ExchV 5.2

COTFiber

RT Subscriber

Fig.1 DLC Network

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Exchange

C

O

T

V 5.2 interface

RT

RT

Subs

Subs

Fibre links

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COT SUPPORTS

POTS

64 kbps E 1

ISDN Basic & Primary rate

Pay phone with 16 KHz metering pulse can provide 2mbps leased lines also. In future the

DLCs may provide N x 64 kbps services, internetaccess

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Computer

Telephone

BDSU

Computer

Telephone

BDSU

INTERNET

PSTN network

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DIAS FEATURES

basic digital subscriber units (BDSU) or high bit rate digitalsubscriber units (HDSU)

an integrated Access Network (IAN)

BDSU FNS

combines voice and internet data packet on single Copper pair

Consist of RJ11 interface for telephone and one Ethernet port (RJ45) for internet.

Connected to IAN by copper pair.

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central office terminal (COT)

remote terminals (RT)