The document discusses the history and development of the Internet and telecommunications. It describes how the Internet was created to allow computers to share information over long distances. Key pioneers who contributed to the development of the Internet and digital communication technologies are profiled, including Vannevar Bush, Claude Shannon, and Tim Berners-Lee. The document also outlines common uses of the Internet today, such as e-commerce, communication, media/entertainment, and how information travels across the global network of connected devices.

1. Internet and
Telecommunications
Jessa S. Ariño
BSE-4B, CBSUA

2. INTERNET

3. Electronic Newspaper
In the late 1990s newspapers began offering their content on the Internet in record numbers. By
the end of the decade, more than 1,000 North American newspapers offered online versions, most
available to Internet users free of charge. Electronic newspapers spared publishers one of their
highest expenses—newsprint—and many brought publishers additional advertising revenue. The
New York Times on the Web, an excerpt of which is shown here, offers readers the same content as
its print publication as well as stories and features available only in its online version.

4. Online Virtual laboratory

5. INTERNET
 computer-based global information system.
The Internet is composed of many
interconnected computer networks. Each
network may link tens, hundreds, or even
thousands of computers, enabling them to
share information and processing power.

6. Internet Map
http://en.wikipedia.org/wiki/Image:Internet_map_1024.jpg

7. Internet
The Internet lets computers share information. The information travels very fast through wires and
cables. In just seconds, a computer hooked up to the Internet can get information from almost
anywhere in the world!

8. Internet Pioneers

9. Vannevar Bush
 Vannevar Bush established
the U.S. military / university
research partnership that
later developed the
ARPANET. He also wrote
the first visionary
description of the
potential use for
information technology,
inspiring many of the
Internet's creators.
Source: Livinginternet.com

10. Claude Shannon
 The Father of Modern Information
Theory
 Published a ”A Mathematical
Theory of Communication” in
1948t
 Created the idea that all
information could be represented
using 1s and 0s. Called these
fundamental units BITS.
 Created the concept data
transmission in BITS per second.
Source: http://www.research.att.com/~njas/doc/ces5.html

11. J. C. R. Licklider
 Joseph Carl Robnett "Lick" Licklider
developed the idea of a universal
network, spread his vision throughout
the IPTO, and inspired his successors
to realize his dream by creation of the
ARPANET. He also developed the
concepts that led to the idea of the
Netizen.
Source: Livinginternet.com

12. Lawrence Roberts
 Lawrence Roberts was the ARPANET
program manager, and led the overall
system design.
 .
Source: Livinginternet.com

13. Steve Crocker
 Steve Crocker is an Internet and computer
security expert. Steve Crocker Associates, LLC is
a consulting and R&D company specializing in
current Internet and electronic commerce
technologies. Executive DSL, LLC is an ISP
specializing in the integration of Internet-based
services for small and medium businesses.
 Steve Crocker was one of the founders and
chief technology officer of CyberCash, Inc.,
the leading Internet payments company.
Source: www.epf.net

14. Jon Postel
 He has worked in the areas of
computer communication
protocols, especially at the
operating system level and the
application level.
Source: Livinginternet.com

15. Vinton Cerf
Vinton Cerf is co-designer
of the TCP/IP networking
protocol.
Source: Livinginternet.com

16. Robert Kahn
 Bob Kahn is co-designer of the TCP/IP networking
protocol.
 Kahn then began work on development of a standard
open-architecture network model, where any computer
could communicate with any other, independent of
individual hardware and software configuration. He set
four goals for the TCP design:
 Network Connectivity. Any network could connect to
another network through a gateway.
 Distribution. There would be no central network
administration or control.
 Error Recovery. Lost packets would be retransmitted.
 Black Box Design. No internal changes would have to be
made to a computer to connect it to the network;
Source: Livinginternet.com

17. Bob Metcalfe
Robert Metcalfe
 ARPANET engineer and
inventor of Ethernet, and
founder of 3Com
Bob Metcalfe
Copyright 2002, William F. Slater, III, Chicago, IL, USA

18. Christian Huitema
 Christian Huitema joined Microsoft in February
2000, as "architect" in the "Windows Networking &
Communications" group. The group is in charge of
all the networking support for Windows, including
the evolution of TCP/IP support, IPv6, Real-Time
Communication, and Universal Plug and Play
(UPnP). Prior to joining Microsoft, he was chief
scientist, and Telcordia Fellow, in the Internet
Architecture Research laboratory of Telcordia,
working on Internet Quality of Service and Internet
Telephony.
Source: http://conferences.oreillynet.com/cs/p2pweb2001/view/e_spkr/518

19. Tim Berners-Lee
 The inventor of HTML. HyperText Markup
Language (HTML) is the main markup
language for displaying web pages and
other information that can be displayed in a
web browser.
Timothy Berners-Lee
Timothy Berners-Lee, a British computer scientist,
developed the World Wide Web during the 1980s.
Source: w3c.org

20. Internet Growth Trends
 1977: 111 hosts on Internet
 1981: 213 hosts
 1983: 562 hosts
 1984: 1,000 hosts
 1986: 5,000 hosts
 1987: 10,000 hosts
 1989: 100,000 hosts
 1992: 1,000,000 hosts
 2001: 150 – 175 million hosts
 2002: over 200 million hosts
 By 2010, about 80% of the planet will be on the Internet

21. March 2001
Over 115 Million Hosts
(As of Jan. 2001)
Over 407 Million Users
(As of Nov. 2000)
218 of 246 Countries
(As of Jan. 2000)
> 31 Million Domain Names
About 100 TB of Data
Dr. Vint Cerf presents in Chicago
at the Drake Hotel on March 2001
The event was a fund-raiser for the ITRC

22. By September 2002
The Internet Reached Two
Important Milestones:

23. The Internet Host Count
in Real time on September 1, 2002 -
Over 204,000,000 IP Hosts!!!
Chart showing Internet Growth
from Sept. 1, 2001 to Sept. 1, 2002.
Source Netsizer.com

24. USES OF INTERNET

25. The Creation of the Internet
 The creation of the Internet solved the following
challenges:
 Basically inventing digital networking as we know it
 Survivability of an infrastructure to send / receive high-speed
electronic messages
 Reliability of computer messaging

26. Uses of Internet
 Companies use the Internet for electronic
commerce, also called e-commerce,
including advertising, selling, buying,
distributing products, and providing customer
service. In addition, companies use the
Internet for business-to-business transactions,
such as exchanging financial information
and accessing complex databases.

27. Marketing and the Internet
The Internet enables marketers to promote products and services to millions
of potential customers through the World Wide Web. This Web site provides
information about a product designed to keep vegetables fresh.

28. •Businesses and institutions use the Internet for voice and video
conferencing and other forms of communication that enable
people to telecommute (work away from the office using a
computer). The use of e-mail speeds communication between
companies, among coworkers, and among other individuals
A dozen Indonesian students gathered at the U.S. Embassy in Jakarta(at left in the split-screen video monitor) had the opportunity
to query their American high school counterparts on their interests, experiences and culture during the interactive video link-up
recently at NASA Dryden's Aerospace Exploration Gallery in Palmdale, Calif.

30. Uses of Internet
 Media and entertainment companies run
online news and weather services over the
Internet, distribute music and movies, and
actually broadcast audio and video,
including live radio and television programs.

32.  File sharing services let individuals swap
music, movies, photos, and applications,
provided they do not violate copyright
protections.

34.  Online chat allows people to carry on
discussions using written text. Instant
messaging enables people to exchange text
messages; share digital photo, video, and
audio files; and play games in real time.

36. Uses of Internet
 Scientists and scholars use the Internet to
communicate with colleagues, perform
research, distribute lecture notes and course
materials to students, and publish papers and
articles.

38.  Individuals use the Internet for
communication and entertainment.

40. HOW THE INTERNET WORKS
 Internet Access
 How Information Travels Over the Internet
 Network Names and Addresses
 Client/Server Architecture
 Electronic Mail
 Other Internet Applications
 Bandwidth

41. Internet Access
 Internet access refers to the communication
between a residence or a business and an ISP
that connects to the Internet. Access falls into
three broad categories: dedicated, dial-up, and
wireless/ satellite.
 With dedicated access, a subscriber’s computer
remains directly connected to the Internet at all
times through a permanent, physical connection.
Example. DSL (digital subscriber line) and cable
modem
 A DSL sends data across the same wires that
telephone service uses, and cable modems use
the same wiring that cable television uses.

42. Digital subscriber line

43. Cable modem

44.  Satellite Internet access, in which a computer
grabs an Internet signal from orbiting satellites
via an outdoor satellite dish.

46.  Dial-up is the least expensive access
technology, but it is also the least convenient.
To use dial-up access, a subscriber must have
a telephone modem, a device that connects
a computer to the telephone system and is
capable of converting data into sounds and
sounds back into data. The user’s ISP provides
software that controls the modem.

47. Telephone modem

48. How Information Travels Over the
Internet
Internet Topology
Connecting individual computers to each other creates networks. The Internet is a series of
interconnected networks. Personal computers and workstations are connected to a Local Area Network
(LAN) by either a dial-up connection through a modem and standard phone line or by being directly
wired into the LAN. Other modes of data transmission that allow for connection to a network include T-1
connections and dedicated lines. Bridges and hubs link multiple networks to each other. Routers
transmit data through networks and determine the best path of transmission.

49. How Information Travels Over the
Internet
 A series of rules known as computer
communication protocols specify how packet
headers are formed and how packets are
processed.
 The set of protocols used for the Internet is
named TCP/IP after the two most important
protocols in the set: the Transmission Control
Protocol and the Internet Protocol. TCP/IP
protocols enable the Internet to automatically
detect and correct transmission problems.

50. Network Names and Addresses
 To be connected to the Internet, a computer must be
assigned a unique number, known as its IP (Internet
Protocol) address. Each packet sent over the Internet
contains the IP address of the computer to which it is being
sent. Intermediate routers use the address to determine
how to forward the packet. Users almost never need to
enter or view IP addresses directly. Instead, to make it
easier for users, each computer is also assigned a domain
name; protocol software automatically translates domain
names into IP addresses.
 Users encounter domain names when they use
applications such as the World Wide Web. Each page of
information on the Web is assigned a URL (Uniform
Resource Locator) that includes the domain name of the
computer on which the page is located. Other items in the
URL give further details about the page. For example, the
string http specifies that a browser should use the http
protocol, one of many TCP/IP protocols, to fetch the item.

51. Client/Server Architecture
 In a client/server architecture, some application programs
act as information providers (servers), while other
application programs act as information receivers (clients
 A single client can access many different servers, and a
single server can be accessed by a number of different
clients. Usually, a user runs a client application, such as a
Web browser, that contacts one server at a time to obtain
information.
 To supply information to others, a computer must run a
server application. Although server software can run on
any computer, most companies choose large, powerful
computers to run server software because the company
expects many clients to be in contact with its server at any
given time. A faster computer enables the server program
to return information with less delay.

52. Electronic Mail
 Electronic mail, or e-mail, is a widely used
Internet application that enables individuals
or groups of individuals to quickly exchange
messages, even if they are separated by
long distances.

53. Other internet applications
 Telnet application enables a user to
interactively access a remote computer.
Telnet gives the appearance that the user’s
keyboard and monitor are connected
directly to the remote computer.
 Doing so is faster and less expensive than
using a dial-up modem.

54.  File Transfer Protocol (FTP), is used to
download files from an Internet site to a user’s
computer. The FTP application is often
automatically invoked when a user
downloads an updated version of a piece of
software. Applications such as FTP have been
integrated with the World Wide Web, making
them transparent so that they run
automatically without requiring users to open
them. When a Web browser encounters a
URL that begins with ftp:// it automatically
uses FTP to access the item.

55.  Newsgroup application software allows
a user to obtain a copy of selected articles
from a local news server or to use e-mail to
post a new message to the newsgroup. The
system makes newsgroup discussions
available worldwide.

56.  Voice Over IP (VoIP) allows individuals
and businesses to make phone calls over the
Internet. Low-cost services (some of them
free) often transfer calls via personal
computers (PCs) equipped with microphones
and speakers instead of the traditional
telephone handset. But a growing number of
services operate outside the PC, making calls
via a special adapter that connects to a
traditional telephone handset.

57. Bandwidth
 Is used to refer to various bit-rate measures,
representing the available or consumed data
communication resources expressed in bits/second
or multiples of it (kilobits/s, megabits/s etc.).
 A dial-up telephone modem can transfer data at
rates up to 56 kbps; DSL and cable modem
connections are much faster and can transfer at a
few mbps. The Internet connections used by
businesses can operate at 45 mbps or more, and
connections between routers in the heart of the
Internet may operate at rates from 2,488 to 9,953
mbps (9.953 gigabits per second).

58. TELECOMMUNICATIONS

59. Telecommunications
 Telecommunication is
the transmission of information over
significant distances to communicate.
 Telecommunications, devices and systems
that transmit electronic or optical signals
across long distances.

60. TELECOMMUNICATIONS SYSTEMS
 Telegraph
Radio Telegraph Operators
Navy radio telegraph operators on
shore type messages to ships at sea
in this photo. Radio telegraph
transmitters send typed messages
by radio waves to receiving stations
located within broadcasting range of
the transmitter. Early radio
telegraphs transmitted keystrokes
into electric pulses, which the
receiving telegraph would translate
into letters.

61. Samuel F. B. Morse
Samuel F. B. Morse was a
successful painter and professor
before he turned to experiments in
electromagnetism. Morse pioneered
telegraph use in the United States
in the 1840s, and developed, with
help from other scientists, the dot-
and-dash system known as Morse
Code used to send telegraph
messages.

62.  Telegraph, system of communication
employing electrical apparatus to transmit
and receive signals in accordance with a
code of electrical pulses. Originally the term
telegraphy referred to any form of
communication over long distances in which
messages were transmitted by signs or
sounds.

63.  Telegraph services use both wireline and
wireless media for transmissions.
 A message sent by telegraph was called a
telegram. Telegrams were printed on paper
and delivered to the receiving party by the
telegraph company.
 With the invention of the radio in the early
1900s, telegraph signals could also be sent by
radio waves.

64. Telegraph
In 1837 the first electrical telegraph instruments were invented by Samuel Morse in
the United States and by Sir Charles Wheatstone and Sir William F. Cooke in Britain.
Morse sent the first public telegraph message in 1844. Pictured here is the original
Morse receiving device.

65. How to use a telegraph?
 To send a telegram you may hand deliver or
telephone your message to a telegraph
office. There, an operator enters the message
into a computer, which then translates it into
code and routes it to its destination. And the
receiving end, machines translate the
encoded message back into words and print
it out. The telegraph office may hand deliver
or telephone the message to the person
receiving it.

66. Telephone
Alexander Graham Bell
Alexander Graham Bell’s
attempts to electrically
transmit speech resulted in
a patent for the telephone
in 1876. Bell founded the
Bell Telephone Company to
manufacture telephones
and operate the telephone
network. Bell’s company,
later known as AT&T Corp.,
grew to dominate the
telecommunications
industry until a 1984
antitrust suit divested the
company of its local
telephone networks.

67. Telephone
Telephone Control Center
Long distance telephone circuits are maintained in telephone control centers. The
number of calls on a given circuit are monitored, and problems are identified and
resolved. If there is a problem, calls can be switched to alternate circuits while
workers search for the cause.

68.  The telephone network also
uses both wireline and
wireless methods to deliver
voice communications
between people, and data
communications between
computers and people or
other computers. Digital
transmission via fiber-optic
cables is now used in some
sections of the telephone
network that send large
amounts of calls over long
distances.

69. Teletype, Telex, and Facsimile
Transmission
 The teletype, essentially a printing telegraph, is
primarily a point-to-multipoint system for sending
text. The teletype converts the same pulses used by
telegraphs into letters and numbers, and then prints
out readable text.

70. teletype

71.  Telex is primarily a point-to-point system
that uses a keyboard to transmit typed
text over telephone lines to similar
terminals situated at individual company
locations.

72. telex

73.  Fax machines contain an optical scanner
that converts text and graphics into digital, or
machine-readable, codes. This coded
information is sent over ordinary analog
telephone lines through the use of a modem
included in the fax machine. The receiving fax
machine’s modem demodulates the signal and
sends it to a printer also contained in the fax
machine.

74. Facsimile Machine
Fax Machine
 Facsimile (fax) transmission involves machines designed to transmit graphical
information via normal telephone lines. After a special fax number is dialed and the
phone connection established, documents are fed through the machine, which
takes approximately one to six minutes to scan and convert the information into
electrical impulses.

75. Radio
 Radio is used mostly as a public medium,
sending commercial broadcasts from a
transmitter to anyone with a radio receiver
within its range, so it is known as a point-to-
multipoint medium.
 Radios transmit and receive communications
at various preset frequencies. Radio waves
carry the signals heard on AM and FM radio, as
well as the signals seen on a television set
receiving broadcasts from an antenna.

77.  Television is primarily a public broadcasting
medium, using point-to-multipoint technology
that is broadcast to any user within range of
the transmitter. Televisions transmit news and
information, as well as entertainment.
 Commercial television is broadcast over very
high frequency (VHF) and ultrahigh
frequency (UHF) radio waves and can be
received by any television set within range of
the transmitter.

79. Global Positioning and Navigation
Systems
Launching a GPS Satellite
A Navstar global positioning system
(GPS) satellite is launched into orbit by
a Delta rocket. GPS satellites
continuously transmit data about the
satellite’s position and the current
time. Military and civilian navigators
use the information gathered from
several satellites to compute their own
position.

80.  The United States Global Positioning System (GPS)
and the Russian Global Orbiting Navigation Satellite
System (GLONASS) are networks of satellites that
provide highly accurate positioning information from
anywhere on Earth. Both systems use a group of
satellites that orbit around the north and south poles
at an altitude of 17,500 km (10,900 mi). These
satellites constantly broadcast the time and their
location above Earth.

81.  A GPS receiver picks up broadcasts from
these satellites and determines its position
through the process of triangulation. Using
the time information from each satellite, the
receiver calculates the time the signal takes
to reach it. Factoring in this time with the
speed at which radio signals travel, the
receiver calculates its distance from the
satellite. Finally, using the location of three
satellites and its distance from each satellite,
the receiver determines its position.

82. Personal Computers
Computer Networking
Networks are connections between groups of computers and associated devices that allow
users to transfer information electronically. The local area network shown on the left is
representative of the setup used in many offices and companies. Individual computers are
called work stations (W.S.), and communicate to each other via cable or telephone line
linking to servers.

83.  Personal computers use telecommunications
to provide a transmission link for the delivery
of audio, video, text, software, and
multimedia services.

84.  Electronic mail, or e-mail, is a key attraction
of the Internet and a common form of
computer telecommunications. E-mail is a
text-based message delivery system that
allows information such as typed messages
and multimedia to be sent to individual
computer users. Local e-mail messages
(within a building or a company) typically
reach addressees by traveling through wire-
based internal networks.

85. Voice Over Internet Protocol
(VOIP)
 Voice Over Internet Protocol (VOIP) is a
method for making telephone calls over the
Internet by sending voice data in separate
packets, just as e-mail is sent.

86. HOW TELECOMMUNICATIONS
WORKS
 Creating and Receiving the Signal
-Telegraphs, telephones, radio, and television all
work by modifying electronic signals, making the
signals imitate, or reproduce, the original
message. This form of transmission is known as
analog transmission.
Devices such as the telegraph and telephone relay
messages by creating modulated electrical
impulses, or impulses that change in a systematic
way. These impulses are then sent along wires,
through the air as radio waves, or via other media
to a receiver that decodes the modulation.

87.  Broadcast radio and cellular radio telephones
are examples of devices that create signals by
modulating radio waves. A radio wave is one
type of electromagnetic radiation, a form of
energy that travels in waves. Microwaves are
also electromagnetic waves, but with shorter
wavelengths and higher frequencies. In
telecommunications, a transmitter creates and
emits radio waves.

88.  Broadcast television works in a similar fashion.
A television camera takes the light reflected
from a scene and converts it into an
electronic signal, which is transmitted over
high-frequency radio waves. A television set
contains a tuner that receives the signal and
uses that signal to modulate the images seen
on the picture tube.

89.  Computers and other types of electronic
equipment, however, transmit digital
information. Digital technologies convert a
message into an electronic or optical form
first by measuring different qualities of the
message, such as the pitch and volume of a
voice, many times.
 Digital information can be transmitted faster
and more clearly than analog signals,
because the impulses only need to
correspond to two digits and not to the full
range of qualities that compose the original
message, such as the pitch and volume of a
human voice.

90.  Computers do this with a device called
a modem, which is short for
modulator/demodulator. A modem
converts the stream of 1s and 0s from a
computer into an analog signal that can
then be transmitted over the telephone
network, as a speaker’s voice would. The
modem of the receiving computer
demodulates the analog sound signal
back into a digital form that the
computer can understand.

91. b. Transmitting the Signal
Telephone Switching Hub
The telephones in a large office building must still be manually
connected together with wires. In the central switching hub pictured
here, several connections come together.

92.  Telecommunications systems deliver messages using
a number of different transmission media, including
copper wires, fiber-optic cables, communication
satellites, and microwave radio. One way to
categorize telecommunications media is to consider
whether or not the media uses wires.
 Wire-based (or wireline) telecommunications provide
the initial link between most telephones and the
telephone network and are a reliable means for
transmitting messages. Telecommunications without
wires, commonly referred to as wireless
communications, use technologies such as cordless
telephones, cellular radio telephones, pagers, and
satellites. Wireless communications offer increased
mobility and flexibility. In the future some experts
believe that wireless devices will also offer high-
speed Internet access.

93. c. Wires and Cables
 Wires and cables were the original medium
for telecommunications and are still the
primary means for telephone connections.
Wireline transmission evolved from telegraph
to telephone service and continues to
provide the majority of telecommunications
services. Wires connect telephones together
within a home or business and also connect
these telephones to the nearest telephone
switching facility.

94.  Other wireline services employ coaxial cable,
which is used by cable television to provide
hundreds of video channels to subscribers. Much
of the content transmitted by the coaxial cable
of cable television systems is sent by satellite to a
central location known as the headend. Coaxial
cables flow from the headend throughout a
community and onward to individual residences
and, finally, to individual television sets. Because
signals weaken as distance from the headend
increases, the coaxial cable network includes
amplifiers that process and retransmit the
television signals.

95. d. Fiber-Optic Cables
 Fiber-optic cables use specially treated glass that
can transmit signals in the form of pulsed beams of
laser light. Fiber-optic cables carry many times more
information than copper wires can, and they can
transmit several television channels or thousands of
telephone conversations at the same time.
 Already fiber optic cables provide the high
capacity, 'backbone' links necessary to carry the
enormous and growing volume of
telecommunications and Internet traffic.

96. Fiber-Optic Cables

97. e. Radio Wave
How Wireless Communications Work
Cellular radio telephones, also known as cell phones, communicate by sending radio signals
to a cell tower. Each cell tower has a certain range within which it can receive the radio
signals. The range of each tower overlaps with that of another tower so as a mobile cell
phone user travels, communication is uninterrupted. To communicate with the user of a
wired telephone, the cell phone radio signals are routed from the cell tower to a mobile
switching center, which in turn routes the signals to the telephone company. The signals
then travel over telephone lines to reach a wired telephone.

98.  Wireless telecommunications use radio waves,
sent through space from one antenna to
another, as the medium for communication.
Radio waves are used for receiving AM and FM
radio and for receiving television. Cordless
telephones and wireless radio telephone
services, such as cellular radio telephones and
pagers, also use radio waves. Telephone
companies use microwaves to send signals over
long distances. Microwaves use higher
frequencies than the radio waves used for AM,
FM, or cellular telephone transmissions, and they
can transmit larger amounts of data more
efficiently.

99.  Microwaves have characteristics similar to those
of visible light waves and transmit pencil-thin
beams that can be received using dish-shaped
antennas. Such narrow beams can be focused
to a particular destination and provide reliable
transmissions over short distances on Earth. Even
higher and narrower beams provide the high-
capacity links to and from satellites. The high
frequencies easily penetrate the ionosphere (a
layer of Earth’s atmosphere that blocks low-
frequency waves) and provide a high-quality
signal.

100. f. Communications Satellites
Satellite Telephone
A telephone company employee
displays a handset used in the
firm's satellite telephone system.
Satellite telephones enable direct
communications to telephone
networks from anywhere on the
globe. Users can also
communicate even if no wired or
cellular telephone network exists.

101.  Iridium Satellite

102.  Communications satellites provide a means of
transmitting telecommunications all over the
globe, without the need for a network of wires
and cables. They orbit Earth at a speed that
enables them to stay above the same place
on Earth at all times. This type of orbit is called
geostationary or geosynchronous orbit
because the satellite’s orbital speed operates
in synchronicity with Earth’s rotation.

103.  The satellites receive transmissions from
Earth and transmit them back to
numerous Earth station receivers
scattered within the receiving coverage
area of the satellite.
 Communications satellites are used by
telephone and television companies to
transmit signals across great distances.
Ship, airplane, and land navigators also
receive signals from satellites to determine
geographic positions.