Best fit topology - LO1 part I

LEVEL III

1. Compiled By Abenezer A.
MARY HELP TVET COLLEGE
Unit of Competence
Determine Best-Fit Topology
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Learning Outcome
L01 Identify key information source
L02 Determine user needs
L03 Develop best topology
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L01 Identify key information source
IdentifyInformationrepositories.
Identify organizational documentation requirements.
Extractinformationfromkeystakeholders.
Informationgatheringtechniques.
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4. Compiled By Abenezer A.
Definition of Computer Networks
ComputerNetworkisacollectionofsystemanddevices
exchangingdataoversomeformofmedia.
Twocomputersaresaidtobeinterconnectediftheyare
abletoexchangeinformation.
Theconnectioncanbeviaacopperwire;fiberoptics,
microwaves,infrared,andcommunicationsatellites.
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5. Compiled By Abenezer A.
Definition of Computer Networking
Networkingisinformationitself.
Informationtransmittedacrossanetworkcanbe
includevoice,video,ordata(text,presentation,
pictureandsoon).
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Network vs. Networking
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Communication Components
Datacommunicationistheexchangeofinformationbetweentwoagents.
Forexchangeofinformationtheinformationshouldbetransmittedfromone
pointtoanotherthroughatransmissionmediacalledChannel.
Therearefivecomponentsindatacommunicationsystem.
–Message
–Sender
–Receiver
–Mediumand
–Protocol
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8. Compiled By Abenezer A.
Communication Components (cont…)
1.Message:theinformationtobecommunicated
(text,numbers,pictures,sound,video-orcombinations)
2.Sender:thedevicethatsendsthemessage(computer,videocamera,…)
3.Receiver:thedevicethatreceivesthemessage.
4.Medium:thephysicalpathbywhichamessagetravelsfromsender
toreceiver.
5.Protocol:asetofrulesthatcoordinatestheexchangeof
information.Boththesenderandthereceivershouldfollowthesame
protocoltocommunicatedata.
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9. Compiled By Abenezer A.
Types of Network
Networksmaybeclassified
accordingtoawidevarietyof
characteristics.suchas
–Geographicalcoverage
(size)
–Configuration(architecture)
–Ownership etc.
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10. Compiled By Abenezer A.
Types of Network based on geographical coverage (size)
Basedonsize,thereareFourtypesofnetwork:-
LocalAreaNetwork(LAN):
oItssmallerinsizeusuallyprivatelyownedandlinksdevices
inasingleoffice,buildingorcampus.
oLANworksunderitsownlocaldomainandcontrolled
centrally.
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11. Compiled By Abenezer A.
Cont….
WideAreaNetwork(WAN):
oSpanshugegeographicareawhich
mayspanacrossterritoryand
evenawholecountry,continent
oCoveringlargegeographicarea;
mayutilizepublic,leased[rented],
or privatecommunications
equipment.
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Cont….
MetropolitanAreaNetwork(MAN):designedtoextendoveranentire
city;itmaybeasinglenetworkorinterconnectedLANs.coverslarge
geographicarealikecity
PersonalAreaNetwork(PAN):meantforoneperson;
oe.g.awirelessnetworkconnectingacomputerwithitsmouse,
keyboardandprinter
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13. Compiled By Abenezer A.
The following table summarizes the above classification
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Inter-Processor
Distance
Processors Located in
same
1m Square meter
10m Room
100m Building
1km Campus
10km City
100km Country
1000km Continent
10000km Planet
Personal Area Network
Local Area Network
Metropolitan Area Network
Wide Area Network
Internet

14. Compiled By Abenezer A.
Types of Network based on configuration
Basedonthetypeofcomputerinanetwork
(configurationorarchitecture),aredividedintotwo
broadcategories.
–Peer-to-peer
–Client/Server
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15. Compiled By Abenezer A.
Cont….
Peer-to-peer
–Therearenodedicatedservers,andthereisnohierarchyamongthe
computers.
–Eachnodeconsideredasequalintermsofresourcesharingand
responsibilities
Pros
•Easytosetup
•Lessexpensive
•Demandsreasonablelevelofskilltoadminister
•Userisabletocontroltheirownresources
Cons
•Only < 10 nodes
•Very low level security
•Performance suffers when a computer is accessed
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16. Compiled By Abenezer A.
Cont…
Peer-to-peer networks are good choices for
environments where:
oThere are 10 users or fewer
oUsers share resources, such as printers, but no
specialised servers exist
oSecurity is not an issue
oThe organization and the network will experience
only limited growth within the foreseeable future
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Cont….
ClientServerModel
–Consistsofagroupclients
connectedtoaserver.
–Serversislargesystemwith
higherprocessingspeed,
memory andharddisk
capacitywhoseroleina
networkistoprovideservices
andresourcestousers.
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18. Compiled By Abenezer A.
Cont….
Advantages of client/server architecture
–Sharing Resources
–Security
–Number of Users -A server-based network can support thousands of
users
Disadvantage of client/server architecture
–more complex to install, configure, and manage
–Expensive
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19. Compiled By Abenezer A.
Network Topology
Topology is simply the layout of your network hosts and media.
The topology can refer to how the network actually looks(the
physical topology), as well as how the data travels on your
network(referred to as the logical topology).
On first steps in designing your network is to decide on its
topology.
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20. Compiled By Abenezer A.
Types of Network Topology
PhysicalTopology:-ofanetworkreferstohowthe
networkactuallylooksfrombird’seyeview-thephysical
cablinglayoutofthenetworkitself.
LogicalTopology:-isreferstothepaththedata
actuallytravelsonitswaythroughthenetwork.
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Cont…
Physical Topology
Logical Topology:-IP address
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Factors that affect the choice of one topology over another:
–Type of equipment the network needs.
–Capabilities of the equipment.
–Growth of the network.
–Method the network is managed.
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23. Compiled By Abenezer A.
Logical Topologies
Thelogicaltopologyofanetworkdetermineshowthe
hostscommunicateacrossthemedium.
Thetwomostcommontypesoflogicaltopologiesare
Broadcast(Bus)and
Tokenpassing(Ring).
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24. Compiled By Abenezer A.
Physical topologies
The five different physical topologies are
1.Bus
2.Star
3.Ring
4.Mesh
5.Hybrid
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25. Compiled By Abenezer A.
Bus Topology
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Terminator
Terminator

26. Compiled By Abenezer A.
Bus Topology (cont..)
A Bus topology Consists of all device connecting to a single wire –a coaxial
cable.
It is often referred to as a “linear bus” because all nodes are connected in a
single communication channel
The bus permits only one pair of nodes to establish communication at a time.
In a bus topology, all computers are connected to a shared communication line,
calleda trunk or a backbone. The computers are connected to the backbone using
T-connectors. Both ends of the backbone use terminators(50-ohm) in order to
prevent reflection of signals or bounced signal.
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27. Compiled By Abenezer A.
Bus Topology (cont..)
•Iftheterminatorismissingorispurposelyremoved,thedata
transmissionsaredisrupted.Thereisnocentraldeviceoranyspecial
configuration.Abustopologyisnormallyimplementedwithcoaxial
cable.
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28. Compiled By Abenezer A.
Bus Topology (cont..)
Communication on the Bus
Computers on a bus topology network communicate by addressing data to a
particular computer and sending out that data on the cable as electronic
signals.
Only one computer can ‘talk’ on a network at a time.
A media access method (protocol) called CSMA/CDis used to handle the
collisions that occur when two signals are placed on the wire at the same time.
The bus topology is passive topology. In other words, the computers on the
bus simply ‘listen’ for a signal; they are not responsible for moving the signal
along.
Signals are broadcastto all stations
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29. Compiled By Abenezer A.
Bus Topology (cont..)
CommunicationontheBus(Cont….)
Tounderstandhowcomputerscommunicateonabus,youneed
tobefamiliarwiththreeconcepts:
1.Sendingthesignal
2.Signalbounce
3.Terminator
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30. Compiled By Abenezer A.
Bus Topology (cont..)
SendingtheSignal
Networkdataintheformofelectronicsignalsissenttoallthecomputersonthe
network.Onlythecomputerwhoseaddressmatchestheaddressencodedinthe
originalsignalacceptstheinformation.Allothercomputersrejectthedata.
Onlyonecomputeratatimecansendmessages.Becauseonlyonecomputerat
atimecansenddataonabusnetwork,thenumberofcomputersattachedtothe
buswillaffectnetworkperformance.

31. Compiled By Abenezer A.
Bus Topology (cont..)
Signal Bounce
The data, or electronic signal, is sent to the entire network, it travels from
one end of the cable to the other.
If the signal is allowed to continue continuous, it will keep bouncing back
and out along the cable and prevent other computers from sending signals.
Therefore, the signal must be stopped after it has had a chance to reach
the proper destination address.

32. Compiled By Abenezer A.
Bus Topology (cont..)
Terminator
To stop the signal from bouncing, a component called a terminatoris placed at
each end of the cable to absorb free signals.
Absorbing the signal clears the cable so that other computers can send data.
A break in the cable will bounce signal and all network activity will stop. The
network will not work because it has unterminated cables

33. Compiled By Abenezer A.
Network Expansion in bus topology
Asthephysicalsizeofthesitegrows,thenetworkwillneedtogrowaswell.
Cableinthebustopologycanbeextendedbyoneofthetwofollowingmethods
Acomponentcalledabarrelconnectorcanconnecttwopiecesofcabletogether
tomakealongerpieceofcable.However,connectorsweakenthesignaland
shouldbeusedcarefully.
Onecontinuouscableisbettertoconnectingseveralsmalleroneswith
connectors.Usingtoomanyconnectorscanpreventthesignalfrombeing
correctlyreceived.BNC(BayonetNeill–Concelman)
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34. Compiled By Abenezer A.
Network Expansion in bus topology
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Network Expansion in bus topology
Adevicecalledarepeatercanbeusedtoconnecttwocables.
Arepeateractuallyboostthesignalbeforeitsendsthesignalonitsway.
Arepeaterboostingaweakenedsignal.Arepeaterisbetterthanaconnectorora
longerpieceofcablebecauseitallowsasignaltotravelfartherandstillbecorrectly
received.
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36. Compiled By Abenezer A.
Advantages of Bus Topology
•Easy to connect a computer or peripheral to a
linear bus.
•Requires less cable length than a star topology.
•Failure of a single node does not terminate the
network
•If a cablethat connect the nodes with the
backbone fails, the network does not fail
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37. Compiled By Abenezer A.
Disadvantages of Bus Topology
•Entire network shuts down if there is a break in the main
cable(backbone).
•Terminatorsare required at both ends of the backbone
cable.
•Difficult to identify the problem if the entire network
shuts down.
•Less fault tolerant
•Network can slow down in heavy traffic.
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39. Compiled By Abenezer A.
Star Topology
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Star Topology
Inthestartopology,cablesegmentsfromeachcomputerareconnectedtoacentralized
componentcalledahub.
TheHUBoffersacommonconnectionforallstationsonthenetwork.Eachstationhasitsown
directcableconnectiontothehub.Inmostcases,thismeansmorecableisrequiredthanfora
bustopology.However,thismakesaddingormovingcomputersarelativelyeasytask;simply
plugthemintoacableoutletonthewall.
If a cable is cut, it only affects the computer that was attached to it. This eliminates the single
point of failure problem associated with the bus topology. (Unless, of course, the hub itself goes
down.)
Star topologies are normally implemented using twisted pair cable, specifically unshielded
twisted pair (UTP). The star topology is probably the most common form of network topology
currently in use.

41. Compiled By Abenezer A.
Cont.…..
Inastarnetwork,eachnode(fileserver,workstations,andperipherals)is
connectedtoacentraldevicecalledahub.
Thehubtakesasignalthatcomesfromanynodeandpassesitalongtoallthe
othernodesinthenetwork.
Thehub,switchmanagesandcontrolsallfunctionsofthenetwork.
Thestartopologyreducesthechanceofnetworkfailurebyconnectingallof
thesystemstoacentralnode.

42. Compiled By Abenezer A.
Advantages of a Star Topology
Easy to install and wire (implementation).
No disruptions to the network when connecting or removing
devices.
Easy to detect faults and to remove parts.
Easy to manage and centralized control
Simple access protocols.
Easy to locate problems (cable/workstations)
Easier to expand than a bus or ring topology.
Easy to detect faults and to remove parts
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43. Compiled By Abenezer A.
Disadvantages of a Star Topology
RequiresmorecablelengththanaBustopology.
Ifthehub,switchfails,nodesattachedare
disabled.
Moreexpensivethanlinearbustopologiesbecause
ofthecostofthehubs,etc.
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44. Compiled By Abenezer A.
Ring Topology
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45. Compiled By Abenezer A.
Ring Topology
The ring topology connected in the form of closed loop. A single communication
channel is often implemented to provide the connectivity.
Data from the sending node circulate around the ring until it reaches the
destination.
Unlike the bus topology, there are no terminated ends; the signal travels a
unidirectional or bi-directional. In a unidirectional ring, data moves in one direction
only. In a bi-directional ring, data moves in both directions, but in one direction at a
time.
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46. Compiled By Abenezer A.
Ring Topology
Singlenodefailuremayparalyzethetransmissionofdatatoasetofnodesina
unidirectionalring.Butmessagescanbesenttonodesineithersideoftheaffected
node
Thesignalstravelaroundtheloopinonedirectionandpassthrougheachcomputer,
whichcanactasarepeatertoboostthesignalandsenditontothenextcomputer.
Thismaderingtopologytobecalledactivetopology.
Notethat while this topology functions logically as ring, it is physically wired as a star.
The central connector is not called a hub but a Multi station Access Unitor MAU.
Rings are normally implemented using twisted pair or fiber-optic cable.
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47. Compiled By Abenezer A.
Communication on the Ring Topology
Under the ring concept, a signal is transferred sequentially via a "token" from one
station to the next.
When a station wants to transmit, it "grabs" the token, attaches data and an address
to it, and then sends it around the ring. The token travels along the ring until it
reaches the destination address.
The receiving computer acknowledges receipt with a return message to the sender.
The sender then releases the token for use by another computer.
Each station on the ring has equal access but only one station can talk at a time.
This type of network topology is very organized. Each node gets to send the data
when it receives an empty token. This helps to reduces chances of collision. Also in
ring topology all the traffic flows in only one direction at very high speed.
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48. Compiled By Abenezer A.
Advantages of Ring Topology
GrowthofsystemhasminimalimpactonperformanceorExtra
computerscanbeaddedeasilywithlittleeffectonperformance
Allstationshaveequalaccess.
Additionalcomponentsdonotaffecttheperformanceofnetwork.
Transmissionofdataisfairlysimpleasitonlytravelsinonedirection
Nodatacollisions
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49. Compiled By Abenezer A.
Disadvantages of Ring Topology
Ifoneworkstationorportgoesdown,theentirenetworkgetsaffected.
MAU’sandnetworkcardsareexpensiveascomparedtoEthernetcardsandhubs.
Ifasinglemachineisswitchedoff,thenetworkdoesn'twork
Ifacablebreaks,thenetworkdoesn'twork
Datamustpassthrougheverycomputeruntilitreachesitsdestination.
Thiscanmakeitslowerthanothernetworklayouts.
Ifthereareanyproblemswiththenetwork,theycanbedifficultto
identifythecause.
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50. Compiled By Abenezer A.
Mesh Topology
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51. Compiled By Abenezer A.
Mesh Topology
Ameshtopologynetworkofferssuperiorredundancyandreliability.
Inameshtopology,eachcomputerisconnectedtoeveryothercomputerbyseparatecabling.
InternetisMeshTopology.
Thisconfigurationprovidesredundantpathsthroughoutthenetworksothatifonecablefails,
anotherwilltakeoverthetraffic.
Whileeaseoftroubleshootingandincreasedreliabilityaredefiniteadvantages,thesenetworksare
expensivetoinstallbecausetheyusealotofcabling.
Youcancalculatethenumberofcablesusedinmeshtopologyusingthefollowingformula:
–NoofCable=n(n-1)/2,wherenisnoofcomputerusedinmeshtopology.
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52. Compiled By Abenezer A.
Example
Calculate the number of cables used for 6 computers in mesh
topology?
=n(n-1)/2 =6(6-1)/2 =6*5/2 =15
Calculate the number of cables used for 10 computers in mesh
topology?
= 45

53. Compiled By Abenezer A.
Advantages of Mesh topology
Datacanbetransmittedfromdifferentdevicesatthesametime.
Thistopologycanwithstandhightraffic.
Evenifoneofthecomponentsfailsthereisalwaysanalternative
present.Sodatatransferdoesn’tgetaffected.
Expansionandmodificationintopologycanbedonewithout
disruptingothernodes.
MostFaultTolerant
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54. Compiled By Abenezer A.
Disadvantages of Mesh topology
Overall costof this network is way too high as compared to
other network topologies.
Set-up and maintenance of this topology is very difficult.
Even administration of the network is very complex.
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55. Compiled By Abenezer A.
Hybrid Topology
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Hybrid Topology
Itiscombinationofanytwoormorenetworktopologies.
Theseexamplescanoccurwheretwobasicnetworktopologies,
whenconnectedtogether,canstillrememberthebasicnetwork
character,andthereforenotbeahybridnetwork.
–Star-Bus
–Star-Ring
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57. Compiled By Abenezer A.
Hybrid Topology
StarBus
ThestarbusThetopologyiscombinedwiththelinearbusinlarge
networks.Insuchcasesthelinearbusprovidesabackbonethatconnects
multiplestars
Inastar-bustopology,severalstartopologynetworksarelinkedtogether
withlinearbustrunks.
Ifonecomputergoesdown,itwillnotaffecttherestofthenetwork.The
othercomputerscancontinuetocommunicate.Ifahubgoesdown,all
computersonthathubareunabletocommunicate.Ifahubislinkedto
otherhubs,thoseconnectionswillbebrokenaswell.
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Hybrid Topology
StarRing
Thestarring(sometimescalledastar-wiredring)appears
similartothestarbus.Boththestarringandthestarbusare
centeredinahubthatcontainstheactualringorbus.
Linear-bustrunksconnectthehubsinastarbus,whilethe
hubsinastarringareconnectedinastarpatternbythemain
hub.
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59. Compiled By Abenezer A.
Advantages of a Hybrid Topology
Itisextremelyflexible.
Itisveryreliable.
Scalable
Effective
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Disadvantages of a Hybrid Topology
Expensive(costlyofhub)
Complexityofdesign
Costlyinfrastructure
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Tree Topology

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Tree Topology
Atreetopology(hierarchicaltopology)canbeviewedasacollection
ofstarnetworksarrangedinahierarchy.
Thistreehasindividualperipheralnodeswhicharerequiredto
transmittoandreceivefromoneotheronlyandarenotrequiredto
actasrepeatersorregenerators.
Thetreetopologyarrangeslinksandnodesintodistincthierarchies
inordertoallowgreatercontrolandeasiertroubleshooting.
Thisisparticularlyhelpfulforcolleges,universitiesandschoolsso
thateachoftheconnecttothebignetworkinsomeway.
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63. Compiled By Abenezer A.
Advantages of a Tree Topology
Point-to-point wiring for individual segments.
Supported by several hardware and software vendors.
All the computers have access to the larger and their immediate
networks.
•Disadvantages of a Tree Topology
Overall length of each segment is limited by the type of cabling used.
If the backbone line breaks, the entire segment goes down.
More difficult to configure and wire than other topologies.

64. Compiled By Abenezer A.
Summary on Network Topologies
The physical layout of computers on a network is called a topology.
There are four primary topologies: star, bus, ring, and mesh.
Topologies can be physical(actual wiring) or logical(the way they work).
In a bus topology, the computers are connected in a linear fashion on a single cable.
Bus topologies require a terminatoron each end of the cable.
In a star topology, the computers are connected to a centralized hub.
Mesh topologies connect all computers in a network to one another with separate cables.
In a token-ring topology, the computers are connected physically in a star shape, but
logically in a ring or circle. The data is passed from one computer to another around the
circle.
Hubsare used to centralize the data traffic and localize failures. If one cable breaks, it
will not shut down the entire network.

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Topology Advantages Disadvantages
Bus
Use of cable is economical.
Media is inexpensive and easy to work with.
System is simple and reliable.
Bus is easy to extend.
Network can slow down in heavy traffic.
Problems are difficult to isolate.
Cable break can affect many users.
Ring
System provides equal access for all computers.
Performance is even despite many users.
Failure of one computer can impact the rest of
the network. Problems are hard to isolate.
Network reconfiguration disrupts operation.
Star
Modifying system and adding new computers is easy.
Centralized monitoring and management are possible.
Failure of one computer does not affect the rest of the
network.
If the centralized point fails, the network fails.
Mesh
System provides increased redundancy and reliability as
well as ease of troubleshooting.
System is expensive to install because it uses a
lot of cabling.
Selecting a topology

66. Compiled By Abenezer A.
Self check Questions on network topology
Exercise 1.1: Case Study Problem
•A small, independent, business/home/life insurance
company consisting of an owner, a business manager, an
administrator, and four agents decides to implement a
network. The company occupies half of a small building
in an office park. Their volume of business had been
stable for the past three years, but recently it has been
increasing. To handle the increased business volume, two
new agents will be hired.
The Following Figure illustrates the current arrangement.

67. Compiled By Abenezer A.
Self check Questions on network topology
•Everyone in the company has a computer, but the business manager has the only
printer. These computers are not connected by any form of networking. When agents
need to print a document, they must first copy the file to a flash disk, then carry it to the
business manager's computer, where they are finally able to print it. Similarly, when
staff members want to share data, the only means available is to copy the data on one
computer to a flash disk and insert the disk in another computer.
•Recently, problems have arisen. The business manager is spending too much time
printing other people's documents; and it is frequently unclear which copy of a given
document is the current and authoritative version.
•Your task is to design a network for this company. To clarify the task of choosing a
solution, you ask some questions. Circle the most appropriate answers to the following
questions:
•Which network topology would be most appropriate in this situation?
Bus
Ring
Star
Mesh
Star bus
Star
ring

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Cont…..
Due Respect
For Your Attention