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Basics of Data Communication and Computer Networking :: 33

2
BASICS OF DATA COMMUNICATION
AND COMPUTER NETWORKING

2
...
Generated
information is not useful in itself
...
Often information
must be transmitted from one location to another
...
Here, we will be concerned with
the hardware, software and procedures used in data
communication
...
Advances in communication technology, combined
with rapidly evolving computer technology, have made possible
much of the progress in the field
...

Telecommunication refers to the use of telephone, telegraph,
and radio or television facility to transmit information, either
directly or via computer
...


2
...




describe communication protocols and data transmission
modes
...




describe different components of computer network



identify different types of network

2
...
Networks are communication system
designed to convey information from a point of origin to a point
of destination
...
The operative word is communication, the
transfer of information from one device to another
...
Telephone
networks are long network
...
Communication is possible
only with wired and wireless connectivity of the computers with
each other
...
Data must be received by the intended device
or user and only by that device or user
...
Data
that have been altered in transmission and left uncorrected
are unusable
...
Data delivered late are useless
...
This kind of
delivery is called real-time transmission
...
3
...
(see fig
...
1)

Basics of Data Communication and Computer Networking :: 35

1
...
Receiver
3
...
Message
5
...
The medium is the channel over which the
message is sent and the protocol is the set of rules that guides
how the data is transmitted from encoding to decoding
...
The message
is the data that is being communicated
...
1 : Data Communication Components

Transmitter: The transmitter is the device that sends the
message
...

Receiver: The receiver is the device that receives the message
...


36 :: Computer and Office Applications

Medium: The transmission medium is the physical path by
which a message travels from sender to receiver
...

Message: The message is the transmission (data) to be
communicated
...

Protocol: A protocol is a set of rules that governs data
communication
...
Without a protocol, two devices may
be connected but not communicating, just as a person speaking
German cannot be understood by a person who speaks only
Japanese
...
4 COMMUNICATION MEDIA
Following are the major communication devices which are
frequently used:


Wire Pairs: Wire pairs are commonly used in local telephone
communication and for short distance digital data
communication
...
Using
these wire pairs data transmission speed is normally 9600
bits per second in a distance of 100 metre
...
Twisted-pair cabling
consist of copper wires that are twisted into pairs
...
Computer networking cabling (wired
Ethernet as defined by IEEE 802
...
The use of two wires twisted together helps
to reduce crosstalk and electromagnetic induction
...
Twisted pair cabling comes in
two forms which are Unshielded Twisted Pair (UTP) and
Shielded twisted-pair (STP) which are manufactured in
different increments for various scenario
...
The cables consist of copper or
aluminum wire wrapped with insulating layer typically of

Basics of Data Communication and Computer Networking :: 37

a flexible material with a high dielectric constant, all of
which are surrounded by a conductive layer
...

Transmission speed range from 200 million to more than
500 million bits per second
...
It transmits light
which can travel over extended distances
...
Transmission
speed may reach trillions of bits per second
...
This capacity may be further
increased by the use of colored light, i
...
, light of multiple
wavelengths
...


Wireless technologies


Terrestrial microwave: Terrestrial microwaves use Earthbased transmitter and receiver
...
Terrestrial microwaves use low-gigahertz
range, which limits all communications to line-of-sight
...

Microwave antennas are usually placed on top of buildings,
towers, hills, and mountain peaks
...
The satellites
are stationed in space, typically 35,400 km (22,000 mi)
(for geosynchronous satellites) above the equator
...


2
...
Bandwidth is the range
of frequencies that is available for the transmission of data
...
The flow of

38 :: Computer and Office Applications

information in such a system is restricted, just as is the flow of
water in the narrow hose
...
The communication data transfer rate is
measured in a unit called baud
...
Therefore, a rate of 300 baud is 300 bits per second
...
Data transmission
rates are from 45 to 300 baud
...




Voiceband handles moderate data transmission volumes
between 300 and 9600 baud
...

Their major application is for telephone voice
communication hence, the term voiceband
...
These
systems provide data transmission rates of 1 million baud
or more
...


2
...
The goal is to produce a signal that can be
transmitted easily and decoded to reproduce the original digital
data
...

A modem modulates outgoing digital signals from a computer
or other digital device to analog signals for a conventional copper
twisted pair telephone line and demodulates the incoming
analog signal and converts it to a digital signal for the digital
device
...
14
...
8 Kbps
modems were temporary landing places on the way to the much
higher bandwidth devices and carriers of tomorrow
...
By comparison, using a digital Integrated Services
Digital Network adapter instead of a conventional modem, the
same telephone wire can now carry up to 128 Kbps
...


2
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1 Types of Modems


Landline Modems



Wireless Modems



LAN Modems

A
...
To connect to PSTN,
these modems have a jack known as RJ-11, or regular
phone jack
...
Landline modems can be further
classified into the followings types:
1
...
Internal
modems usually are cheaper than external modems, but
when problems occur, fixing and troubleshooting the
modem can sometimes prove to be quite difficult
...
Most internal modems come installed in the
computer you buy
...
Internal modems are activated
when you run a communications program and are turned
off when you exit the program
...

Internal modems usually cost less than external modems,
but the price difference is usually small
...
When you want to replace an internal modem
you have to go inside the computer case to make the switch
...
External modems: This device is attached to the back of
the computer by way of a cable that plugs into the modem
port
...
It can
be used with other computers very easily by unplugging it
and plugging it into another computer
...
External modems have their own power
supply and connect with a cable to a computer’s serial port
...

Because external modems have their own power supply,
you can turn off the modem to break an online connection
quickly without powering down the computer
...
You also can monitor your modem’s
connection activity by watching the status lights
...
Voice/data/fax modems: This device can be hooked up
to your telephone and used to send information to your
computer
...
Most computer modems are modems with
faxing capabilities
...
PC Card modem: These modems, designed for portable
computers, are the size of a credit card and fit into the PC
Card slot on notebook and handheld computers
...

Except for their size, PC Card modems are like a
combination of external and internal modems
...
The cards are powered by the computer,
which is fine unless the computer is battery-operated
...

B
...
e
...
)

Basics of Data Communication and Computer Networking :: 41

Using wireless modems, one can connect to a network while
being mobile
...

C
...
LAN modem comes fully
preconfigured for single particular network architecture
such as Ethernet or Token Ring and/or particular network
software such as IPX, NetBIOS, NetBEUI etc
...
6
...
This process
involves modulating and demodulating the computer’s digital
signals into analog signals that travel over the telephone lines
...


2
...
In computer network two
or more computers are linked together with a medium and
data communication devices for the purpose of communicating
data and sharing resources
...

In the network the individual computers, which access shared
network resources, are known as nodes
...
7
...
In this case, you can place a movie
disc (DVD or BD) on the computer that has the player, and
then view the movie on a computer that lacks the player

42 :: Computer and Office Applications


You may have a computer with a CD/DVD/BD writer
or a backup system but the other computer doesn’t have
it
...
7
...
Networks may be classified
according to a wide variety of characteristics such as the
medium used to transport the data, communications protocol
used, scale, topology, and organizational scope
...


2
...
3 Properties of Network
1
...

2
...
The capability of providing access to data and
information on shared storage devices is an important
feature of many networks
...
Share network and computing resources
In a networked environment, each computer on a network
may access and use resources provided by devices on the
network, such as printing a document on a shared network
printer
...


2
...
Not only can you share photos, music files, and
documents, you can also use a home network to save
copies of all of your important data on a different
computer
...




Printer / peripheral sharing: Once a home network is
in place, it’s then easy to set up all of the computers to
share a single printer
...
Other computer peripherals can be shared
similarly such as network scanners, Web cams, and
CD burners
...
You will notice the Internet connection slows
down when several people share it, but broadband
Internet can handle the extra load with little trouble
...




Internet telephone service: Voice over IP (VoIP)
services allows you to make and receive phone calls
through your home network across the Internet
...
Having these products
integrated into your network enables online Internet
gaming, video sharing and other advanced features
...
9 TYPES OF NETWORK
There are many different types of networks
...
9
...
A LAN is useful for
sharing resources like files, printers, games or other
applications
...

Most local area networks are built with relatively inexpensive
hardware such as Ethernet cables, network adapters, and hubs
...
LAN is a computer network that spans a relatively
small area
...
However, one LAN can be connected to other LANs
over any distance via telephone lines and radio waves
...
2
...
Each node (individual computer) in a LAN has its
own CPU with which it executes programs, but it is also able
to access data and devices anywhere on the LAN
...
Users can also use the LAN
to communicate with each other, by sending e-mail or engaging
in chat sessions
...


Basics of Data Communication and Computer Networking :: 45

Fig
...
2 LAN

2
...
2 Wide Area Networks (WANs)
The term Wide Area Network (WAN) usually refers to a network
which covers a large geographical area, and use
communications circuits to connect the intermediate nodes
...

Transmission rates are typically 2 Mbps, 34 Mbps, 45 Mbps,
155 Mbps, 625 Mbps (or sometimes considerably more)
...
9
...
A MAN is a relatively new
class of network, it serves a role similar to an ISP, but for
corporate users with large LANs
...
10 IMPORTANT TERMS USED IN NETWORKING
Voice Messaging
It is a new communication approach which is similar to
electronic mail except that it is audio message rather than text
messages that are processed
...
That sender’s voice signal is then digitized and stored
...
The message is reconverted back into its analog
format when it is delivered or retrieved so that the recipient
hears it as the original sender’s voice on a telephone
...
Each user has a voice mailbox in
secondary storage and special equipment converts the audio
message to and from the digital form
...
Voice mail also makes it easy to include people in the
firm’s environment in a communication network
...
Its job is very simple: anything that comes
in one port is sent out to the others
...
The hub itself is blissfully ignorant of the data being
transmitted
...

Switch
A switch does essentially what a hub does but more efficiently
...
For example, if it sees
traffic from machine A coming in on port 2, it now knows that
machine A is connected to that port and that traffic to machine
A needs to only be sent to that port and not any of the others
...
On busy networks this can make the network significantly
faster
...

Routers come in all shapes and sizes from the small four-port
broadband routers that are very popular right now to the large
industrial strength devices that drive the internet itself
...
For example, broadband
routers include the ability to “hide” computers behind a type
of firewall which involves slightly modifying the packets of
network traffic as they traverse the device
...
The really large routers include the equivalent of a
full-blown programming language to describe how they should
operate as well as the ability to communicate with other routers
to describe or determine the best way to get network traffic
from point A to point B
...
It
retimes and regenerates the signals to proper amplitudes and
sends them to the other segments
...
Repeaters require a small amount of time to regenerate
the signal
...
Many network architectures limit the number of repeaters
that can be used in a row
...

Bridge
A bridge reads the outermost section of data on the data packet,
to tell where the message is going
...

Bridges can be programmed to reject packets from particular
networks
...
In our
case the bridge can read the ethernet data which gives the
hardware address of the destination address, not the IP address
...
Only a special bridge
called a translation bridge will allow two networks of different

48 :: Computer and Office Applications

architectures to be connected
...
The
hardware address is also called the MAC (media access control)
address
...
If the address is
not in the bridging table, the packet is forwarded to all
segments other than the one it came from
...




Source route bridging: The source computer provides path
information inside the packet
...
It functions
at the network and data link layers of the OSI network model
...
It can translate TCP/IP
to AppleTalk so computers supporting TCP/IP can communicate
with Apple brand computers
...
Gateways will start at the lower level
and strip information until it gets to the required level and
repackage the information and work its way back toward the
hardware layer of the OSI model
...
11 TELECONFERENCING
The term teleconferencing refers to electronic meetings that
involve people who are at physically different sites
...
Three different types of teleconferencing exist:
audio teleconferencing, video teleconferencing and computer
conferencing
...
11
...
The conference call was the first form of audit
conferencing and is still in use
...

Audio conferencing does not require a computer
...

Audio conferencing is best suited for firms that are spread over
a wide area
...


2
...
2 Video Conferencing:
Video conferencing is the use of television equipment to link
geographically dispersed conference participants
...
Like audio
conferencing, video conferencing also does not necessarily
require a computer
...
Generally, participants gather in relatively expensive,
specially equipped rooms that can handle the complexities of
simultaneous video and audio transmission
...

One-Way Video and Audio: Video and audio signals are sent
from a single transmitting site to one or more receiving sites
...

One-Way Video and Two-Way Audio: People at the receiving
sites can talk to people at the transmitting site, while everyone
views the same video images
...
Although this
is the most effective of the electronically aided conferencing
approaches, it can be the most expensive as well
...
11
...
There is a fine line between this system and Email
...
Two factors
determine this application, who uses the system, and the
subject matter
...
Also, the
E-mail system can be used for any purpose
...
Computer conferencing
is more disciplined form of E-mail
...
One of the largest
computer conferences was formed within IBM to include anyone
who had an interest in the IBM PC
...

Computer conferencing differs from audio and video
conferencing because it can be used within a single geographic
site
...


INTEXT QUESTION 2
...
State TRUE or FALSE
(a) The basic components for working of a communication
system are transmitter, medium, receiver, message and
protocol
...


Basics of Data Communication and Computer Networking :: 51

2
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Computers can
communicate with one another through computer networking
...

We discussed about various types of moderns used for data
communications such as land line modems, wireless modems
and LAN modems
...


2
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What is computer network? What are its main objectives?
2
...
14 ANSWER TO INTEXT QUESTIONS
Intext Question 2
...
(a) True (b) True



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