Touch-tone telephone

The invention: 



A push-button dialing system for telephones that

replaced the earlier rotary-dial phone.



The person behind the invention:



Bell Labs, the research and development arm of the American

Telephone and Telegraph Company







Dialing Systems



A person who wishes to make a telephone call must inform the

telephone switching office which number he or she wishes to reach.

A telephone call begins with the customer picking up the receiver

and listening for a dial tone. The action of picking up the telephone

causes a switch in the telephone to close, allowing electric current to

flow between the telephone and the switching office. This signals

the telephone office that the user is preparing to dial a number. To

acknowledge its readiness to receive the digits of the desired number,

the telephone office sends a dial tone to the user. Two methods

have been used to send telephone numbers to the telephone office:

dial pulsing and touch-tone dialing.

“Dial pulsing” is the method used by telephones that have rotary

dials. In this method, the dial is turned until it stops, after which it is

released and allowed to return to its resting position. When the dial

is returning to its resting position, the telephone breaks the current

between the telephone and the switching office. The switching office

counts the number of times that current flow is interrupted,

which indicates the number that had been dialed.



Introduction of Touch-tone Dialing



The dial-pulsing technique was particularly appropriate for use

in the first electromechanical telephone switching offices, because

the dial pulses actually moved mechanical switches in the switching

office to set up the telephone connection. The introduction of

touch-tone dialing into electromechanical systems was made possi-

ble by a special device that converted the touch-tones into rotary

dial pulses that controlled the switches. At the American Telephone

and Telegraph Company’s Bell Labs, experimental studies were

pursued that explored the use of “multifrequency key pulsing” (in

other words, using keys that emitted tones of various frequencies)

by both operators and customers. Initially, plucked tuned reeds

were proposed. These were, however, replaced with “electronic

transistor oscillators,” which produced the required signals electronically.

The introduction of “crossbar switching” made dial pulse signaling

of the desired number obsolete. The dial pulses of the telephone

were no longer needed to control the mechanical switching process

at the switching office. When electronic control was introduced into

switching offices, telephone numbers could be assigned by computer

rather than set up mechanically. This meant that a single

touch-tone receiver at the switching office could be shared by a

large number of telephone customers.

Before 1963, telephone switching offices relied upon rotary dial

pulses to move electromechanical switching elements. Touch-tone

dialing was difficult to use in systems that were not computer controlled,

such as the electromechanical step-by-step method. In about

1963, however, it became economically feasible to implement centralized

computer control and touch-tone dialing in switching offices.

Computerized switching offices use a central touch-tone receiver

to detect dialed numbers, after which the receiver sends the

number to a call processor so that a voice connection can be established.

Touch-tone dialing transmits two tones simultaneously to represent

a digit. The tones that are transmitted are divided into two

groups: a high-band group and a low-band group. For each digit

that is dialed, one tone from the low-frequency (low-band) group

and one tone from the high-frequency (high-band) group are transmitted.

The two frequencies of a tone are selected so that they are

not too closely related harmonically. In addition, touch-tone receivers

must be designed so that false digits cannot be generated when

people are speaking into the telephone.

For a call to be completed, the first digit dialed must be detected

in the presence of a dial tone, and the receiver must not interpret

background noise or speech as valid digits. In order to avoid such

misinterpretation, the touch-tone receiver uses both the relative and

the absolute strength of the two simultaneous tones of the first digit

dialed to determine what that digit is.

A system similar to the touch-tone system is used to send telephone

numbers between telephone switching offices. This system,

which is called “multifrequency signaling,” also uses two tones to

indicate a single digit, but the frequencies used are not the same frequencies

that are used in the touch-tone system. Multifrequency

signaling is currently being phased out; new computer-based systems

are being introduced to replace it.



Impact



Touch-tone dialing has made new caller features available. The

touch-tone system can be used not only to signal the desired number

to the switching office but also to interact with voice-response

systems. This means that touch-tone dialing can be used in conjunction

with such devices as bank teller machines. Acustomer can also

dial many more digits per second with a touch-tone telephone than

with a rotary dial telephone.

Touch-tone dialing has not been implemented in Europe, and

one reason may be that the economics of touch-tone dialing change

as a function of technology. In the most modern electronic switching

offices, rotary signaling can be performed at no additional cost,

whereas the addition of touch-tone dialing requires a centralized

touch-tone receiver at the switching office. Touch-tone signaling

was developed in an era of analog telephone switching offices, and

since that time, switching offices have become overwhelmingly digital.

When the switching network becomes entirely digital, as will

be the case when the integrated services digital network (ISDN) is

implemented, touch-tone dialing will become unnecessary. In the

future, ISDN telephone lines will use digital signaling methods exclusively.



See also: Cell phone; Rotary dial telephone; Telephone switching.

Cell phone

The invention: 



Mobile telephone system controlled by computers

to use a region’s radio frequencies, or channels, repeatedly,

thereby accommodating large numbers of users.



The people behind the invention:



William Oliver Baker (1915- ), the president of Bell

Laboratories

Richard H. Fefrenkiel, the head of the mobile systems

engineering department at Bell











The First Radio Telephones



The first recorded attempt to use radio technology to provide direct

access to a telephone system took place in 1920. It was not until

1946, however, that Bell Telephone established the first such commercial

system in St. Louis. The system had a number of disadvantages;

users had to contact an operator who did the dialing and the

connecting, and the use of a single radio frequency prevented simultaneous

talking and listening. In 1949, a system was developed

that used two radio frequencies (a “duplex pair”), permitting both

the mobile unit and the base station to transmit and receive simultaneously

and making a more normal sort of telephone conversation

possible. This type of service, known as Mobile Telephone Service

(MTS), was the norm in the field for many years.

The history of MTS is one of continuously increasing business usage.

The development of the transistor made possible the design and

manufacture of reasonably light, compact, and reliable equipment,

but the expansion of MTS was slowed by the limited number of radio

frequencies; there is nowhere near enough space on the radio spectrum

for each user to have a separate frequency. In New York City, for

example, New York Telephone Company was limited to just twelve

channels for its more than seven hundred mobile subscribers, meaning

that only twelve conversations could be carried on at once. In addition,

because of possible interference, none of those channels could

be reused in nearby cities; only fifty-four channels were available na-

tionwide. By the late 1970’s, most of the systems in major cities were considered full,

and new subscribers were placed on a waiting list; some people had been waiting

for as long as ten years to become subscribers.

Mobile phone users commonly experienced long delays in getting poor-quality

channels.



The Cellular Breakthrough



In 1968, the Federal CommunicationsCommission (FCC) requested proposals for the

creation of high-capacity, spectrum- efficient mobile systems.

Bell Telephone had already been lobbying for the creation of such a system for some years.

In the early 1970’s, both Motorola and Bell Telephone proposed the use of cellular

technology to solve the problems posed by mobile telephone service.

Cellular systems involve the use of a computer to make it possible to use an area’s

frequencies, or channels, repeatedly, allowing such systems to accommodate many

more users.

A two-thousand-customer, 2100-square-mile cellular telephone

system called the Advanced Mobile Phone Service, built by the

AMPS Corporation, an AT&T subsidiary, became operational in

Chicago in 1978. The Illinois Bell Telephone Company was allowed

to make a limited commercial offering and obtained about fourteen

hundred subscribers. American Radio Telephone Service was allowed

to conduct a similar test in the Baltimore/Washington area.

These first systems showed the technological feasibility and affordability

of cellular service.

In 1979, Bell Labs of Murray Hill, New Jersey, received a patent for such a system.

The inventor was Richard H. Fefrenkiel, head of the mobile systems engineering

department under the leadership of Labs president William Baker.

The patented method divides a city into small coverage areas called “cells,” each served

by lowpower transmitter-receivers. When a vehicle leaves the coverage of one cell,

 calls are switched to the antenna and channels of an adjacent

cell; a conversation underway is automatically transferred

and continues without interruption. Achannel used in one cell can

be reused a few cells away for a different conversation. In this way,

a few hundred channels can serve hundreds of thousands of users.

Computers control the call-transfer process, effectively reducing

the amount of radio spectrum required. Cellular systems thus actually

use radio frequencies to transmit conversations, but because

the equipment is so telephone-like, “cellular telephone” (or “cell

phone”) became the accepted term for the new technology.

Each AMPS cell station is connected by wire to a central switching

office, which determines when a mobile phone should be transferred

to another cell as the transmitter moves out of range during a

conversation. It does this by monitoring the strength of signals received

from the mobile unit by adjacent cells, “handing off” the call

when a new cell receives a stronger signal; this change is imperceptible

to the user.



Impact



In 1982, the FCC began accepting applications for cellular system

licenses in the thirty largest U.S. cities. By the end of 1984, there

were about forty thousand cellular customers in nearly two dozen

cities. Cellular telephone ownership boomed to 9 million by 1992.

As cellular telephones became more common, they also became

cheaper and more convenient to buy and to use. New systems

developed in the 1990’s continued to make smaller, lighter, and

cheaper cellular phones even more accessible. Since the cellular telephone

was made possible by the marriage of communications and

computers, advances in both these fields have continued to change

the industry at a rapid rate.

Cellular phones have proven ideal for many people who need or

want to keep in touch with others at all times. They also provide

convenient emergency communication devices for travelers and

field-workers. On the other hand, ownership of a cellular phone can

also have its drawbacks; many users have found that they can never

be out of touch—even when they would rather be.



William Oliver Baker



For great discoveries and inventions to be possible in the

world of high technology, inventors need great facilities—laboratories

and workshops—with brilliant colleagues. These must

be managed by imaginative administrators.

One of the best wasWilliam Oliver Baker (b. 1915), who rose

to become president of the legendary Bell Labs. Baker started out

as one of the most promising scientists of his generation. After

earning a Ph.D. in chemistry at Princeton University, he joined

the research section at Bell Telephone Laboratories in 1939. He

studied the physics and chemistry of polymers, especially for use

in electronics and telecommunications. During his research career

he helped develop synthetic rubber and radar, found uses

for polymers in communications and power cables, and participated

in the discovery of microgels. In 1954 he ranked among the

top-ten scientists in American industry and asked to chair a National

Research Council committee studying heat shields for

missiles and satellites.

Administration suited him. The following year he took over

as leader of research at Bell Labs and served as president from

1973 until 1979. Under his direction, basic discoveries and inventions

poured out of the lab that later transformed the way

people live and work: satellite communications, principles for

programming high-speed computers, the technology for modern

electronic communications, the superconducting solenoid,

the maser, and the laser. His scientists won Nobel Prizes and legions

of other honors, as did Baker himself, who received dozens

of medals, awards, and honorary degrees. Moreover, he

was an original member of the President’s Science Advisory

Board, became the first chair of the National Science Information

Council, and served on the National Science Board. His

influence on American science and technology was deep and

lasting.



See also : Internet; Long-distance telephone; Rotary dial telephone;

Telephone switching; Touch-tone telephone.