LESSON
7
NETWORK
I.
Consider
the following
questions in
the group
of four. A spokesperson
will report on your discussion
to the
whole group.
1. What do
you know about network connections?
2. What was network created for?
3. What do you know about the advances in
wireless networks?
4. What type of network connection is used in
your town?
II.
Read the text
below and check its
comprehension.
Network
A network has three
layers of components: application software, network software, and network
hardware. Application software consists of computer programs that interface
with network users and permit the sharing of information, such as files,
graphics, and video, and resources, such as printers and disks. One type of
application software is called client-server. Client computers send requests
for information or requests to use resources to other computers, called servers
that control data and applications. Another type of application software is
called peer-to-peer. In a peer-to-peer network, computers send messages and
requests directly to one another without a server intermediary.
Network software consists
of computer programs that establish protocols, or rules, for computers to talk
to one another. These protocols are carried out by sending and receiving
formatted instructions of data called packets. Protocols make logical
connections between network applications, direct the movement of packets
through the physical network, and minimize the possibility of collisions
between packets sent at the same time.
Network hardware is made
up of the physical components that connect computers. Two important components
are the transmission media that carry the computer's signals, typically on wires or fiber-optic cables, and
the network adapter, which accesses
the physical media that link computers, receives packets from network software,
and transmits instructions and requests to other computers. Transmitted
information is in the form of binary digits, or bits (1s and 0s) which the
computer's electronic circuitry can process.
Network Connections
A network has two
types of connections: physical
connections that let computers directly transmit and receive signals and logical,
or virtual, connections that allow computer applications, such as word
processors, to exchange information. Physical connections are defined by the
medium used to carry the signal, the geometric arrangement of the computers
(topology), and the method used to share information. Logical connections are
created by network protocols and allow data sharing between applications on
different types of computers, such as an Apple Macintosh and an International
Business Machines Corporation (IBM) personal computer (PC), in a network. Some
logical connections use client-server application software and are primarily
for file and printer sharing. The Transmission Control Protocol/Internet
Protocol (TCP/IP) suite, originally developed by the United States Department
of Defense, is the set of logical connections used by the Internet, the
worldwide consortium of computer networks. TCP/IP, based on peer-to-peer
application software, creates a connection between any two computers.
The
medium used to transmit information limits the speed of the network, the
effective distance between computers, and the network topology. Copper wires
and coaxial cable provide transmission speeds of a few thousand bits per second
for long distances and about 100 million bits per second (Mbps) for short
distances. Optical fibers carry 100 million to 1 billion bits of information per second over long distances.
Common topologies used to
arrange computers in a network are point-to-point,
bus, star, and ring. Point-to-point topology is the simplest, consisting of two
connected computers. The bus topology is composed of a single link connected to
many computers. All computers on this common connection receive all signals
transmitted by any attached computer. The star topology connects many computers
to a common hub computer. This hub can be passive, repeating any input to all
computers similar to the bus topology, or it can be active, selectively
switching inputs to specific destination computers. The ring topology uses
multiple links to form a circle of computers. Each link carries information in
one direction. Information moves around the ring in sequence from its source to
its destination.
Local
area networks (LANs), which connect computers separated by
short distances, such as in an office or a university campus, commonly use bus,
star, or ring topologies. Wide area networks (WANs), which connect distant
equipment across the country or internationally, often use special leased
telephone lines as point-to-point links.
When computers share
physical connections to transmit information packets, a set of Media Access
Control (MAC) protocols are used to allow information to flow smoothly through
the network. An efficient MAC protocol ensures that the transmission medium is
not idle if computers have information to transmit. It also prevents collisions
due to simultaneous transmission that would waste media capacity. MAC protocols
also allow different computers fair access to the medium.
One type of MAC is
Ethernet, which is used by bus or star network topologies. An Ethernet-linked
computer first checks if the shared medium is in use. If not, the computer
transmits. Since two computers can both sense an idle medium and send packets
at the same time, transmitting computers continue to monitor the shared
connection and stop transmitting information if a collision occurs. Ethernet
can transmit information at a rate of 10 Mbps.
Computers also can use Token Ring MAC protocols, which pass a
special message called a token through the network. This token gives the
computer permission to send a packet of information through the network. If a
computer receives the token, it sends a packet, or, if it has no packet to
send, it passes the token to the next computer. Since there is only one token
in the network, only one computer can transmit information at a time.
Network
Operation and Management
Network management and
system administration are critical for a complex system of interconnected
computers and resources to remain operating. A network manager is the person or
team of people responsible for configuring the network so that it runs
efficiently. For example, the network manager might need to connect computers
that communicate frequently to reduce interference with other computers. The
system administrator is the person or team of people responsible for
configuring the computer and its software to use the network. For example, the
system administrator may install network software and configure a server's file
system so client computers can access shared files.
Networks are subject to hacking, or
illegal access, so shared files and resources must be protected. A network
intruder could eavesdrop on packets being sent across a network or send
fictitious messages. For sensitive information, data encryption (scrambling
data using mathematical equations) renders captured packets unreadable to an
intruder. Most servers also use authentication schemes to ensure that a request
to read or write files or to use resources is from a legitimate client and not
from an intruder.
Future Technologies
and Trends
The wide use of notebooks and other
portable computers drives advances in wireless networks. Wireless networks use
either infrared or radio frequency transmissions to link these mobile computers
to networks. Infrared wireless LANs work only within a room, while wireless
LANs based on radio-frequency transmissions can penetrate most walls. Wireless
LANs have capacities from less than 1 Mbps to 8 Mbps and operate at distances
up to a few hundred meters. Wireless communication for WANS use cellular
telephone networks, satellite transmissions, or dedicated equipment to provide
regional or global coverage, but they have transmission rates of only 2000 to
19,000 bits per second.
New networks must also meet the growing demand for faster transmission
speeds, especially for sound and video applications. One recently developed
network, called an Asynchronous Transfer Mode (ATM) network, has speeds of up
to 625 Mbps and can be used by either LANs or WANs.
In February 1996
Fujitsu Ltd., Nippon Telephone and Telegraph Corpora-tion, and a team of researchers from AT&T succeeded in transmitting
infor-mation through an optical fiber at a
rate of 1 trillion bits per second—the equi-valent of transmitting 300 years of newspapers in a single second. This
was accomplished by simultaneously sending different wavelengths of light, each
carrying separate information, through the optical fiber. If it can be
integrated into a network, this new technology will make it easy, inexpensive,
and incre-dibly fast to send information, such
as video and memory-sensitive three-di-mensional
images.
Comprehension Check Up
1. What is it a network? 2. How many
components does the network pos-sess? 3. What
do you know about physical and logical or virtual connections? What is the
difference between them? 4. What is medium used for? 5. What could you tell me
about topology? What topologies are used to arrange com-puters in a network? 6. When is a set of Media Access Control (MAC)
proto-cols used? 7. At what rate can the
information be transmitted by Ethernet? 8. What message is called a token? 9.
What is a network manager? 10. How is the problem of illegal access solved? 10.
What do you know about wireless networks and how do they operate? 11. What are
the main features of wire-less networks? 12. At what rate do they
operate? 13. What are advantages of applying wireless networks?
III.
Choose the best answer.
1. The word network means …
a) a communication containing some information
sent by radio, telephone or other means; b) a surface; c) a boring novel d) a
media of linking of two or more
computers
2. Peer
to peer network refers to …
a) a message and request sent by computer
directly to one another without a sender intermediary; b) a physical media that
links computers; c) a transmitted information; d) a bank network
3. The word packet
means …
a) an electronic
message; b) a type of application; c) a printer; d)
formatted instructions of
data
4. The word token
deals with …
a) an illegal access; b) a permission; c) a
social activity; d) a special message
5. The verb to provide implies that one should
…
a) supply smth.; b) carry the computer’s
signal; c) rely on smb. ; d) take care of smb.
6. Point-to-point links mean …
a) place on a surface; b) a material used as a
source of heat or power;
c) a village or a small town; d) special leased
telephone line
7. The verb to remain implies that one should …
a) stay in the same place; b) continue; c) be
in the same condition; d) lin-ger
8. The verb to run refers to …
a) to manage;
b) to use; c) to operate; d) to move
9. The best explanation of the word file might
be …
a) any of various types of drawers; b) a card
index, c) an organized collection of related data or material in a computer; d)
a folder
10. The verb to connect means …
a) to unite; b) to put smb. into contact by
telephone; c) to combine; d) to link
11. To reduce implies that one should …
a) make smth. smaller in size, number, etc.; b)
change smth. to a more regular or basic form; c) lessen; d) lose weight
intentionally
12 The word resource
means …
a) a reserve; b) a thing that can be turned to
for help or support; c) a store; d) a supply
13 The best explanation of the word data might
be …
a) information
prepared or stored by a computer; b) an evidence; c) facts or information used
in deciding or discussing smth.; d) secret files
14 The verb to penetrate
implies that one should …
a) enter; b) fill or spread through smb./smth.;
c) bore a hole; d) make a way into or through smth.
15 The best explanation of the word capacity might be …
a) a volume; b) an ability to hold
or continue smth.; c) a power to produce smth.; d) a content.
IV.
Use the
right word from those given
below.
to connect, hub,
collision, to transmit, to link, to process, to run, to install, to penetrate,
to meet, to prevent, advance.
1. Network in computer
science, computer programs used … two or more computers. 2. Transmitted
information is the form of binary digits or bits, which the
computer’s electronic circuitry can ….
3. Physical connections allow computers directly … and receive signals. 4. The
star topology … many computers to a common hub computer. 4. Protocols minimize
the possibility of … between packets sent at the same time. 5. This … can be
passive, repeating any input to all computers similar to the bus topology.
V.
Are the following statements True or False?
VI.
Express the main
idea of
each
part of the text
in one-two sentence.
VII.
Summarize
the text
and be ready to retell it.
VIII.
Tell us about
the advantages or disadvantages of using network.