Telephone Instruments and Signals

Telephone Instruments and Signals

Presented by:

The telephone was invented by at least four

different people in three different countries

1. Alexander Graham Bell

– Scottish

American, generally credited as the

"winner" in the race to invent the

telephone in the period between 1850 and

1876

2. Johann Philipp Reis

– German

3. Antonio Meucci

– Italian

In 1876, at the age of 29, Alexander Graham Bell invented his telephone

Design sketch of the phone

Model of Alexander Graham Bell's Telephone

Famous first words:

"Mr. Watson -- come here -- I want to see you."

"Telephone" (he was one of the first to coin the term) were manufactured by a German firm, and a few more in England.

Das Reis'sche „Telephon” von 1861

“Ein Pferd frisst keinen Gurkensalat.”

- Words supposedly spoken by Philipp Reis

in testing his new telephone invention.

Antonio Meucci Meucci’s Teletrofono – _{speaking Telegraph}

Has been denied fame and fortune only because he lacked $250 and because Bell

himself rifled the files of a patent office, destroying the evidence of Meucci's

Elisha Gray (1835-1901)

Elisha Gray, American inventor, who contested the invention of the telephone with Alexander Graham Bell. He invented a number of telegraphic devices and in 1869 was one of two partners who founded what became Western Electric Company

On February 14, 1876, Bell's telephone patent application was filed at the United States Patent Office; Elisha Gray's attorney filed a caveat for a telephone just a few hours later. On September 12,

1878, patent litigation involving the Bell Telephone Company against Western Union Telegraph

1877 First Commercial Telephone 1878 "Coffin" Style Telephone 1882 Western Electric "three box" Telephone

1880s Desk Telephone

Early 1890s Desk Telephone Mid-1890s Desk Telephone 1890s Western Electric Common Battery Telephone 1890s Strowger Automatic Telephone 1890s Western Electric two box phone 1905 Automatic Electric Strowger Telephone

1900s Magneto Telephone 1910 Western Electric Desk Telephone 1920s Western Electric Dial Telephone 1920s/30s Western Electric Desk Telephone 1940s Western Electric Desk Telephone 1990s Telephone

Main Parts of a Telephone Set:

1. Transmitter / mouthpiece 2. Receiver / earpiece

3. Switch Hook 4. Dialer

Parts of Telephone

Switch Hook / Plunger – also called the cradle; has a lever

spring that is used to initiate or terminate call 2 States:

1. On-Hook – the handset setting when the telephone is idle and the switch is open, thus, no dc current flows through the line.

2. Off-Hook – the condition as soon as the telephone handset is lifted, the switch is closed thus alerting the C.O. to supply a dc current and a dial tone

Parts of Telephone

Dialer

2 Methods:

1. Dial Pulsing or Pulse Dialing – is defined as a momentary on-hook condition that causes loop making and breaking from the telephone set dialer toward the C.O. Commonly used for rotary telephone set.

State of Pulse:

1. make – circuit closed/off-hook 2. break – circuit opened/on-hook

Parts of Telephone

To transmit a digit, it takes 0.1 second per pulse + 0.5

second interdigital delay time

Pulsing speed = number of pulses per second (pps)

Pulsing period = make + break

Example:

How long does it take to dial the number 681-1725 using pulse dialing having an interdigit duration of 0.4 sec.?

Example:

If a switching machine is set to accept pulses at a rate of 10 pulses per second with a 60% break, find the make interval of the switch.

Parts of Telephone

2. Multifrequency Dialing or Dual Tone Multifrequency Dialing (DTMF) – a method that is normally done by combining two of the frequencies in the voice frequency band where the combined frequencies represent one digit recognized by the C.O. Commonly used for touch-tone telephone set.

Example:

How long does it take to dial the number 680-1134 using tone dialing with 0.05 second duration for each digit and 0.05 second duration for interdigit?

Parts of Telephone

Comparison between Rotary & Touch-Tone Dialer:

VS.

Uses make and break techniques

Uses combination of two frequencies

Slow Dialing Fast Dialing

Parts of Telephone

Ringer or Bell:

- device that converts electrical signals from the C.O. to an audible signal alerting the subscriber that a call is in progress

Ringer Circuits:

1. Classical Bell Type Ringer - is a mechanical bell controlled by an electronic coil

2. Electronic Ringer - the coil controlled bell is replaced by modern electronic ringing chip and small speaker

Central Office / Local Exchange Carrier

The C.O. operates to:

1. Provide battery (DC voltage) to a telephone. This DC voltage is used to operate the telephone and to determine when a subscriber has gone off or on-hook.

2. Provide ringing (AC voltage) voltage to a telephone. This AC voltage operates a bell or buzzer in the telephone to alert the subscriber to an incoming call.

3. Provide dial tone when a subscriber goes off-hook

4. Accept the digits dialed by the subscriber when off-hook

5. Provide switching equipment used to connect a subscriber to the telephone number dialed.

Lines and Trunks LEC Interoffice Trunk Interconnection trunk Other Carrier 254123 4 4121234 Subscriber Line LEC Subscriber Line 4245678 Exchange Code = 412 Exchange Code = 424

Network Hierarchy

LEC

TOLL SWITCH

IGF International Gateway Facility – a facility consisting of international transmission, switching and

network management facilities which serve as point of entry and exit in the Philippines of

international traffic between the national network and point/s outside the Philippines

Toll Switch – facility that route long distance

calls over the appropriate

facilities, and deliver them to the local switch that serves the

number being called

Local Exchange Carrier – is a regulatory term in

telecommunications for

so-called local telephone company. It is also referred to as LEC for short

Numbering Concept

Two Numbering Scheme as defined by ITU-T (CCITT):

1. Uniform Numbering – is a scheme in which the length of the subscriber’s number is uniform inside a given numbering area (common is 7 digits). The first three digits identify the local exchange and the last four digits identify the subscriber.

2. Non-uniform Numbering – is a scheme in which the subscriber’s number varies within a given numbering area

Elements of Telephone Number: 1. International Access Code 2. Country Code

3. Area Code

Basic Call Progress

1. On-Hook

2. Off Hook

Basic Call Progress

5. Ringing

6. Talking 4. Dialing

Call Progress Tones

1. Dial Tone – a tone advising that the exchange is ready to receive call

information and inviting the user.to start sending call information. Typically, it can be heard for a maximum period of 20 sec

2. Ring Tone - is a tone returned by receiving equipment that tells a caller that

the phone at that end is ringing

3. Ringback Tone - intermittent audio tone that a caller in a telephone system

hears after dialing a number, when the distant end of the circuit is receiving a ringing signal

Call Progress Tones

4. Busy Tone - an audible or visual signal that indicates that the called number

is occupied or otherwise unavailable

5. Congestion Tone - a tone advising the caller that the groups of lines or

switching equipment necessary for the setting-up of the required call or for the use of a specific service are temporarily engaged

6. Receiver Off-hook signal – creates a very loud tone at the receiver and it’s

purpose is to alert the customer that the telephone’s handset has accidentally gone off-hook and must be placed back onto its cradle

TRANSMISSION MEDIUM

MICROWAVE

FIBER OPTIC CABLE

XDSL MODEM