COMPUTER NETWORK: A computer network is

1. a group of 2 or more computer systems

2. with other computing hardware devices
3. that are linked together through a communication
medium
4. to facilitate communication between connected
systems
5. and information and resource-sharing
among a wide range of users.
Networks are used for the following key reasons:
o facilitate communication via
email! video conferencing! instant messaging! etc.
o enable multiple users to share a
single hardware device like a printer or scanner
o enable file sharing across the
network
o allow for the sharing of software
or operating programs on remote systems
o make information easier to access
and maintain among network users
There are many tyes of networks! in"luding:
#o"al $rea Networks %#$N&
"ersonal Area #etworks $"A#%
&ome Area #etworks $&A#%
Wide $rea Networks %W$N&
'ampus Area #etworks $'A#%
Metroolitan $rea Networks
%M$N&
(nterprise "rivate #etworks
)nternetworks
The 'nternet
Models of Network Comuting:
After we have all the re*uired things for a network! a
structure must be made in order to organi+e the way in
which communication and sharing will occur. This
stru"ture is known as Model of Network Comuting(
here are basically 3 models.
1. 'entrali+ed computing model
2. ,istributed computing model
3. 'ollaborative computing model
Centrali)ed Comuting Model:
he centrali+ed computing model involves the following-
1. All processing takes place in the central! mainframe
computer.
2. erminals are connected to the central computer and
function only as input . output devices.
3. #etworks may be employed to interconnect two or
more mainframe computers.
4. erminals connect only to the mainframe! never to
each other.
*istri+uted Comuting Model:
,istributed computing involves the following-
1. /ultiple computers are capable of operating
independently.
2. asks are completed locally on various computers.
3. #etworks enable the computers to e0change data
and services but do not provide processing assistance.
Colla+orati,e Comuting Model
'ollaborative computing involves the following-
1. /ultiple computers cooperating to perform a task
2. A network that enables the computers to e0change
data and services
3. 1oftware designed to take advantage of the
collaborative environment.
Comuter Networking Models:
'omputer network model defines the category in which
a computer network can be grouped into.
#etworks are divided into two broad categories-
1. "eer to "eer #etwork model
2. 'lient- 1erver #etwork /odel
-( PEER TO PEER NETWORK MO*E#
2hen nodes or workstations perform the same
communication functions! they are referred to as
peers.
)n this network model! both server and client
operations are performed by the same computer.
(ach user administers his.her workstation and the
resources in it.
)n a peer-to-peer network! there are no dedicated
servers! and there is no hierarchy among the
computers.
All the computers are e*ual and therefore are known
as peers.
(ach computer functions as both a client and a
server.
here is no administrator responsible for the entire
network.
he user on each computer determines which data
on that computer is shared on the network.
1ecurity is also managed by the user of the devices.
his model is not *uite secure and is suited for a
small computer networks $with 13 computers or
less% where users do not want to share files.
4ser5s files are decentrali+ed 6 they are not stored in
a single location.
Criteria for sele"ting PEER TO PEER NETWORK
MO*E#
2here ten or fewer users will be sharing resources.
#o server is available.
#obody has the time or knowledge to act as a
network administrator.
here is little or no concerns about security
he organi+ation and the network will e0perience
only limited growth within the foreseeable future.
$d,antages of using eer to eer network model
hey are easy to configure
'omputers communicate easily.
hey don5t re*uire additional server hardware or
software
4sers can manage their own resources.
hey don5t re*uire a network administrator
hey reduce total cost of network setup.
*isad,antages of using eer to eer network model
hey provide a limited number of connections for
shared resources.
'omputers with shared resources suffer from
sluggish performance.
hey don5t allow for central management
4sers are responsible for managing resources. hese
resources include data in shared directories! printers! fa0
cards! and so on.
hey offer very poor security.
C#'ENT .ER/ER NETWORK MO*E#
his is a network model that offers centrali+ed
access to services and devices.
7ne computer plays the role of a server.
)t is the most common type of network architecture
today that provides centrali+ed data storage! security!
manning of applications and network administration.
/ost servers operating system are #ovel #etware!
2indows #! Apple talk! 8inu0! 9anyan :)#(1
etc...
*isad,antages of Client0.er,er model
/ore e0pensive in terms of hardware and
network operating system.
Comle1ity: 0 (0perienced system administrators are
re*uired to manage the systems.
*eenden"e: 0 2hen server goes down! operations will
cease across the network.
$d,antages of Client0.er,er model
1. .e"urity: 0 All ma;or server based systems
provides sophisticated security.
2. $dministration: 0 1ervers are centrali+ed
making them easier to manage.
3. .ta+ility: 0 1erver based systems are designed
to support a wide range of organi+ation si+es.
Additional servers are added to increase
capacity.
4. 2le1i+ility - #ew technology can be easily
integrated into the system.
5. $""essi+ility - 1erver can be accessed remotely
and across multiple platforms.
<. 'lient server networks offer "entrali)ed +a"ku
where data can be stored in one server.
=. hey are best suited for -3 or more users(
Network toology:
)t is the arrangement of the various elements $links!
nodes! etc.% of a computer.
(ssentially! it is the structure of a network! and may
be hysi"al or logi"al(
Physi"al toology refers to the placement of various
components of a network! including device location
and cable installation.
#ogi"al toology shows how data flows within a
network! regardless of its physical design.
*istan"es +etween nodes! hysi"al inter"onne"tions!
transmission rates! and4or signal tyes may differ
+etween two networks! yet their toologies may +e
identi"al.
here are seven basic topologies
Point0to0oint
5us
.tar
Ring or "ir"ular
Mesh
Tree
6y+rid
-( Point0to0Point Toology: he simplest topology
is a permanent link between two endpoints.
7( 5us: 9us opology is the simplest of network
topologies.
)n this type of topology! all the nodes
$computers as well as servers% are connected to
the single cable $called bus%! by the help of
interface $% connectors.
his central cable is the backbone of the
network and is known as 9us $thus the name%.
(very workstation communicates with the other
device through this 9us.
A signal from the source is broadcasted and it travels
to all workstations connected to bus cable.
Although the message is broadcasted but only the
intended recipient! whose )" address matches!
accepts it.
)f the )" address of machine doesn5t match with the
intended address! machine discards the signal.
A terminator is added at ends of the central cable! to
prevent bouncing of signals.
$d,antages %+enefits& of 5us Toology
1. )t is easy to set-up and e0tend bus network.
2. 'able length re*uired for this topology is the least
compared to other networks.
3. 9us topology costs very less. 9us network is mostly
used in small networks. >ood for 8A#.
*isad,antages %*raw+a"ks& of #inear 5us Toology
1% here is a limit on central cable length and number
of nodes that can be connected.
2% ,ependency on central cable in this topology has its
disadvantages. )f the main cable $i.e. bus% encounters
some problem! whole network breaks down.
3% "roper termination is re*uired to dump signals. 4se
of terminators is must.
4% )t is difficult to detect and troubleshoot fault at
individual station.
5% /aintenance costs can go higher with time.
<% (fficiency of 9us network reduces as the number of
devices connected to it increases.
=% )t is not suitable for networks with heavy traffic.
?% 1ecurity is very low because all the computers
receive the sent signal from the source.
8( .tar Toology
)n 1tar topology! all the components of network are
connected to the central device called @hubA which
may be a hub! a router or a switch.
4nlike 9us topology! where nodes were connected to
central cable! here all the workstations are connected
to central device with a point-to-point connection.
1o it can be said that every computer is indirectly
connected to every other node by the help of @hubA.
All the data on the star topology passes through the
central device $hub% before reaching the intended
destination.
&ub acts as a ;unction to connect different nodes
present in 1tar #etwork! and at the same time it
manages and controls whole of the network.
,epending on which central device is used! @hubA
can act as repeater or signal booster.
'entral device can also communicate with other
hubs of different network.
4nshielded wisted "air $4"% cable is used to
connect workstations to central node.
$d,antages of .tar Toology
1. As compared to 9us topology it gives far much
better performance! signals don5t necessarily get
transmitted to all the workstations. A sent signal
reaches the intended destination after passing
through no more than 3-4 devices and 2-3 links.
"erformance of the network is dependent on the
capacity of central hub.
2. (asy to connect new nodes or devices. )n star
topology new nodes can be added easily without
affecting rest of the network. 1imilarly
components can also be removed easily.
3. 'entrali+ed management. )t helps in monitoring
the network.
4. Bailure of one node or link doesn5t affect the rest
of network. At the same time it5s easy to detect the
failure and troubleshoot it.
*isad,antages of .tar Toology
1. oo much dependency on central device has its
own drawbacks. )f it fails whole network goes
down.
2. he use of hub! a router or a switch as central
device increases the overall cost of the network.
3. "erformance and as well number of nodes which
can be added in such topology is depended on
capacity of central device.
4. Ring Toology
)n Cing opology! all the nodes are connected to
each-other in such a way that they make a closed
loop.
(ach workstation is connected to two other
components on either side! and it communicates
with these two ad;acent neighbors.
,ata travels around the network! in
one direction. 1ending and receiving of data takes
place by the help of 7D(#.
$d,antages of Ring Toology
1. his type of network topology is very
organi+ed.
2. (ach node gets to send the data when it
receives an empty token. his helps to
reduces chances of collision.
3. )n ring topology all the traffic flows in
only one direction at very high speed.
4. (ven when the load on the network
increases! its performance is better than
that of 9us topology.
5. here is no need for network server to
control the connectivity between
workstations.
<. Additional components do not affect the
performance of network.
=. (ach computer has e*ual access to
resources.
*isad,antages of Ring Toology
1. (ach packet of data must pass through
all the computers between source and
destination.
2. his makes it slower than 1tar topology.
3. )f one workstation or port goes down!
the entire network gets affected.
4. #etwork is highly dependent on the wire
which connects different components.
5. #etwork cards are e0pensive as
compared to (thernet cards and hubs.
9( Mesh Toology
)n a mesh network topology! each of the
network node! computer and other
devices! are interconnected with one
another.
(very node not only sends its own
signals but also relays data from other
nodes.
A true mesh topology is the one where
every node is connected to every other
node in the network.
his type of topology is very e0pensive
as there are many redundant
connections! thus it is not mostly used in
computer networks.
)t is commonly used in wireless
networks.
Blooding or routing techni*ue is used in
mesh topology.
Tyes of Mesh Network toologies:0
1% 2ull Mesh Toology: 0
)n this! like a true mesh! each component is
connected to every other component.
(ven after considering the redundancy factor
and cost of this network! its main advantage is
that the network traffic can be redirected to other
nodes if one of the nodes goes down.
Bull mesh topology is used only for backbone
networks.
7& Partial Mesh Toology:0
his is far more practical as compared to full
mesh topology.
&ere! some of the systems are connected in
similar fashion as in mesh topology while rests
of the systems are only connected to 1 or 2
devices.
)n partial mesh! the workstations are Eindirectly5
connected to other devices.
his one is less costly and also reduces
redundancy.
$d,antages of Mesh toology
1. ,ata can be transmitted from different devices
simultaneously. his topology can withstand
high traffic.
2. (ven if one of the components fails there is
always an alternative present. 1o data transfer
doesn5t get affected.
3. (0pansion and modification in topology can be
done without disrupting other nodes.
*isad,antages of Mesh toology
1. here are high chances of redundancy in many
of the network connections.
2. 7verall cost of this network is way too high as
compared to other network topologies.
3. 1et-up and maintenance of this topology is very
difficult.
4. Administration of the network is tough.
:( Tree Toology
ree opology integrates the
characteristics of 1tar and 9us opology.
)n ree opology! the number of 1tar
networks is connected using 9us.
he main cable seems like a main stem
of a tree! and other star networks as the
branches.
)t is also called E1anded .tar
Toology.
(thernet protocol is commonly used in
this type of topology.
$d,antages of Tree Toology
1. )t is an e0tension of 1tar and bus
opologies! so in networks where these
topologies canFt be implemented
individually for reasons related to
scalability! tree topology is the best
alternative.
2. (0pansion of #etwork is possible and
easy.
3. &ere! we divide the whole network into
segments $star networks%! which can be
easily managed and maintained.
4. (rror detection and correction is easy.
5. (ach segment is provided with dedicated
point-to-point wiring to the central hub.
<. )f one segment is damaged! other
segments are not affected.
*isad,antages of Tree Toology
1. 9ecause of its basic structure! tree
topology! relies heavily on the main bus
cable! if it breaks whole network is
crippled.
2. As more and more nodes and segments
are added! the maintenance becomes
difficult.
3. 1calability of the network depends on
the type of cable used.
;( 6y+rid Toology
)n this type of topology we integrate two or
more different topologies to form a new topology
which has good points! as well as weaknesses! of all
the constituent basic topologies rather than having
characteristics of one specific topology.
his combination of topologies is done
according to the re*uirements of the
organi+ation.
$d,antages of 6y+rid Network Toology
1. Relia+le: 4nlike other networks! fault detection
and troubleshooting is easy in this type of
topology. he part in which fault is detected can
be isolated from the rest of network and re*uired
corrective measures can be taken! without
affecting the functioning of rest of the network.
2. ."ala+le: )t5s easy to increase the si+e of
network by adding new components! without
disturbing e0isting architecture.
3. 2le1i+le: &ybrid #etwork can be designed
according to the re*uirements of the
organi+ation and by optimi+ing the available
resources. 1pecial care can be given to nodes
where traffic is high as well as where chances of
fault are high.
4. Effe"ti,e: &ybrid topology is the combination
of two or more topologies! so we can design it in
such a way that strengths of constituent
topologies are ma0imi+ed while there
weaknesses are neutrali+ed. Bor e0ample we saw
Cing opology has good data reliability
$achieved by use of tokens% and 1tar topology
has high tolerance capability $as each node is not
directly connected to other but through central
device%! so these two can be used effectively in
hybrid star-ring topology.
*isad,antages of 6y+rid Toology
1. Comle1ity of *esign: 7ne of the biggest
drawbacks of hybrid topology is its design. )t5s
not easy to design this type of architecture and
it5s a tough ;ob for designers. 'onfiguration and
installation process needs to be very efficient.
2. Costly 6u+: he hubs used to connect two
distinct networks! are very e0pensive. hese
hubs are different from usual hubs as they need
to be intelligent enough to work with different
architectures and should be function even if a
part of network is down.
3. Costly 'nfrastru"ture: As hybrid architectures
are usually larger in scale! they re*uire a lot of
cablesG cooling systems! sophisticate network
devices! etc.
Token Ring Network
A oken Cing network is a local area
network $8A#% in which all computers
are connected in a ring or star topology
A bit- or token-passing scheme is used
in order to prevent the collision of data
between two computers that want to
send messages at the same time.
6ow it works<
1. (mpty information frames are
continuously circulated on the ring.
2. 2hen a computer has a message to
send! it inserts a token in an empty
frame $this may consist of simply
changing a 3 to a 1 in the token bit part
of the frame% and inserts a message and
a destination identifier in the frame.
3. he frame is then e0amined by each
successive workstation. )f the
workstation sees that it is the destination
for the message! it copies the message
from the frame and changes the token
back to 3.
4. 2hen the frame gets back to the
originator! it sees that the token has been
changed to 3 and that the message has
been copied and received. )t removes the
message from the frame.
5. he frame continues to circulate as an
HemptyH frame! ready to be taken by a
workstation when it has a message to
send.
*ata 2rame 2ormat in Token Ring Network
2rame field *es"rition
.tart delimiter )ndicates start of the frame
$""ess "ontrol indicates the frameFs priority and
whether it is a token or a data frame
2rame "ontrol 'ontains either /edia Access
'ontrol information for all
computers or Hend stationH
information for only one computer
2rame field *es"rition
*estination indicates the address of the
address computer to receive the frame
.our"e address indicates the computer that sent
the frame
*ata 'ontains the data being sent
2rame "he"k 'ontains 'C' error-checking
se=uen"e information
End delimiter indicates the end of the frame
2rame status tells whether the frame was
recogni+ed! copied! or whether the
destination address was available
)n a oken Cing network! the hub is known by several
names as follows-
/A4 $/ultistation Access 4nit%.
/1A4 $/ulti1tation Access 4nit%.
1/A4 $1mart /ultistation Access 4nit%.
#OC$# $RE$ NETWORK %#$N&
A lo"al area network %#$N& is a computer network that
interconnects computers in a limited area such as a
1tart
,elimiter
Access 'ontrol
,estination
Address
1ource Address
,ata
Brame check
1e*uence
(nd ,elimiter
Brame 1tatus
Brame 'ontrol
home! school! computer laboratory! or office building
using any communication medium.
2E$TURE. O2 #$N
-( #imited >eograhi" #imits:0 A 8A# is designed
for a small area. >enerally it spans a single office!
work group floor in a building! or in a campus etc.
8A# uses different protocols or rules for
information transmission.
7( #imited No( of Users: 0 /ost 8A# supports )
number of users usually around five or ten. /ore
users can be supported by connecting different
8A#s together! which gives better results than
making oneG by network of the nature of /A#.
8( Relia+ility ? .ta+ility: 0 8A#1 tend to be very
reliable failures on a 8A# are mostly due to wrong
or improper installation and monitoring. 1oftware
that comes along with a 8A# provides a number of
useful programs like error-detection! prevention of
transmission loss and e0cellent security features.
@( 2le1i+ility: 0 /a;or development in 8A#s today is
fle0ibility they offer. (arlier versions would support
only one type of desktop computers. odayFs
advanced 8A#s however can support different types
of computers. he fle0ibility also e0tends to
operating systems I storage media.
9( E1anda+le: 0 /ost 8A#s can be e0panded easily.
/ore nodes $erminal% can be added. Although! this
depends on design of cabling plan $opology% also.
Also 8A#s can have more servers oil same network
and a user at a terminal can connect to one or many
servers and work comfortably.
:( .e"urity ? $dministration:- A 8A#
administrator is one who supervises the operation of a
8A#. &e takes care of tasks like adding or deleting
users! creating passwords providing authori+ations
and other resources like printers and backing up data.
All these tasks can be performed without much
difficulty since both hardware and software are *uite
easy to manage.
$d,antages of #$N
-( (asy to share devices $printers! scanners!
e0ternal drives%
7( (asy to share data $homework! pictures.%
8( 9uild a comple0 enough one and you may get
enough e0perience to get a new ;ob.
@( 'ost of 8A# 1etup is low.
*isad,antages of #$N
-( "ower - a good 8A# is re*uired to be on all
the times.
7( 1ecurity - each computer and device become
another point of entry for undesirables.
8( 4pkeep - when things go wrong or the
software gets updated.
@( Brustration if having a problem setting up.
9( A lot of times a network shares one )nternet
connection - if all computers running at once! can
reduce speed for each.
:( Area covered is limited.
Metroolitan $rea Network %M$N&
1. A metroolitan area network
$M$N% is a computer network that
usually connects a city or a large
campus.
2. A /A# usually interconnects a
number of local area networks
$8A#s% using a high-capacity
backbone technology! such as fiber-
optical links
3. )t provides up-link services to wide
area networks $or 2A#% and the
)nternet.
4. )ts geographic scope falls between a
2A# and 8A#.
2E$TURE. O2 M$N
he network si+e falls intermediate between
8A#s and 2A#s. A /A# typically covers an area
of between 5 and 53 km diameter. /any /A#s
cover an area the si+e of a city.
he /A#! its communications links and
e*uipment are generally owned by either a group of
users or by a single network provider who sells the
service to the users.
A /A# often acts as a high speed network
to allow sharing of regional resources $similar to a
large 8A#%.
)t is also fre*uently used to provide a shared
connection to other networks using a link to a 2A#.
$d,antages of M$N
1. )t provides a good back bone for a large network and
provides greater access to 2A#.
2. A /an usually encompasses several blocks of a city or
an entire city.
3. 'overs more area than a 8A#.
*isad,antages of M$N
1% /ore cable re*uired for a /A# connection from one
place to another
2% the large the network becomes difficult to mange
3% it is difficult to make the system secure from hackers
and industrial geographical regions.
W'*E $RE$ NETWORK %W$N&
Wide $rea Network $2A#% is a telecommunication
network that covers a broad area i.e.! any network that
links across metropolitan! regional! or national
boundaries.
2E$TURE. O2 W$N
1. 2A# may use a similar topology as a 8A#! but it uses
different protocols to send packets over a wide distance.
2. A 2A# is much more spanned in the distance it
can send information to.
3. A 2A# uses point-to-point connections over a wide
distance.

$d,antages Of W$N
'overs a large geographical area so long distance
businesses can connect on the one network
1hares software and resources with connecting
workstations
/essages can be sent very *uickly to anyone else
on the network. hese messages can have pictures!
sounds! or data included with them $called
attachments%.
(0pensive things $such as printers or phone lines to
the internet% can be shared by all the computers on the
network without having to buy a different peripheral for
each computer.
(veryone on the network can use the same data.
his avoids problems where some users may have older
information than others.
1hare information.files over a larger area
large network cover
*isad,antages Of W$N
Are e0pensive and generally slow
#eed a good firewall to restrict outsiders from
entering and disrupting the network
1etting up a network can be an e0pensive and
complicated e0perience. he bigger the network the
more e0pensive it is.

1ecurity is a real issue when many different people
have the ability to use information from other
computers. "rotection against hackers and viruses adds
more comple0ity and e0pense.
7nce set up! maintaining a network is a full-time
;ob which re*uires network supervisors and technicians
to be employed.
)nformation may not meet local needs or interests
:ulnerable to hackers or other outside threats.