Data Communication and networks note ppt

Data communication and network
1. Introduction to Data Communication:
Data communication refers to the exchange of data between devices through a transmission medium such as cables, fiber optics, or wireless signals. The primary goal is to ensure the accurate and efficient transfer of data from one point to another. This process involves several key components:

Sender: The device that originates the message.
Receiver: The device that receives the message.
Transmission Medium: The physical path through which the message travels (e.g., twisted-pair wire, coaxial cable, fiber-optic cable, or air for wireless communication).
Message: The data being communicated, which can be in the form of text, numbers, images, audio, or video.
Protocol: A set of rules governing the data communication process, ensuring that the devices involved can interpret and understand the transmitted data correctly.
2. Types of Data Communication:

Simplex: Data flows in one direction only. Examples include keyboards and monitors.
Half-Duplex: Data flows in both directions, but not simultaneously. Walkie-talkies are a common example.
Full-Duplex: Data flows in both directions simultaneously, like in telephone conversations.
3. Network Fundamentals:
A network is a collection of interconnected devices that can communicate with each other. Networks can be categorized based on their size, range, and structure.

4. Types of Networks:

Local Area Network (LAN): Covers a small geographic area, like a home, office, or building. Typically uses Ethernet or Wi-Fi.
Wide Area Network (WAN): Spans a large geographic area, often a country or continent. The internet is the largest WAN.
Metropolitan Area Network (MAN): Covers a larger geographic area than a LAN but smaller than a WAN, such as a city.
Personal Area Network (PAN): A small network typically within the range of an individual, such as a Bluetooth connection between devices.
5. Network Topologies:

Bus Topology: All devices are connected to a single central cable.
Star Topology: All devices are connected to a central hub.
Ring Topology: Devices are connected in a circular fashion.
Mesh Topology: Devices are interconnected, with multiple paths for data transmission.
Hybrid Topology: A combination of two or more different topologies.
6. Protocols and Standards:
Protocols are rules that govern data communication. Some common protocols include:

TCP/IP (Transmission Control Protocol/Internet Protocol): The fundamental suite for internet communications.
HTTP (HyperText Transfer Protocol): Used for transferring web pages.
FTP (File Transfer Protocol): Used for transferring files.
SMTP (Simple Mail Transfer Protocol): Used for sending emails.
Standards ensure interoperability between different devices and networks. Some key organizations that develop and maintain these standards include:

IEEE (Institute of Electrical and Electronics Engineers)
IETF (Internet Engineering Task Force)
ISO (International Organization for Standardization).

1. McGraw-Hill ©The McGraw-Hill Companies, Inc., 2000
Data Communications and
Networks
Alidu Abubakari
Street Sign
STOP
Line of Sight
Reflection
Diffraction
Scattering
Transmitter
Receive
r
Buildings
Earth surface

2. 1.2
Chapter 1
Introduction

3. Course Instructor
ALIDU ABUBAKARI
M.Eng, Electronics and Control
Engineering (wireless communications)
BSc Telecommunication Engineering
0550672434
[email protected]

4. Course Outline

5. 1.5
1-1 DATA COMMUNICATIONS
Thetermtelecommunicationmeanscommunicationata
distance.Theworddatareferstoinformationpresented
inwhateverformisagreeduponbythepartiescreating
andusingthedata.Datacommunicationsarethe
exchangeofdatabetweentwodevicesviasomeformof
transmissionmediumsuchasawirecable.
Components
Data Representation
Data Flow
Topics discussed in this section:

6. The effectiveness of a data communications system depends on four
fundamental characteristics: delivery, accuracy, timeliness, and jitter.
1.Delivery. The system must deliver data to the correct destination.
Data must be received by the intended device or user and only by
that device or user.
2.Accuracy. The system must deliver the data accurately. Data that
have been altered in transmission and left uncorrected are
unusable.
3.Timeliness. The system must deliver data in a timely manner. Data
delivered late are useless. In the case of video and audio, timely
delivery means delivering data as they are produced, in the same
order that they are produced, and without significant delay. This
kind of delivery is called real-time transmission.
4.Jitter. Jitter refers to the variation in the packet arrival time. It is
the uneven delay in the delivery of audio or video packets. For
example, let us assume that video packets are sent every 30 ms.If
some of the packets arrive with 30-ms delay and others with 40-ms
delay, an uneven quality in the video is the result.

7. 1.7
Figure 1.1 Five components of data communication
1. Message. The message is the information (data) to be communicated.
Popular forms of information include text, numbers, pictures, audio, and
video.
2. Sender. The sender is the device that sends the data message. It can
be a computer, workstation, telephone handset, video camera, and so on.

8. 1.8
Figure 1.1 Five components of data communication
3. Receiver. The receiver is the device that receives the message. It can
be a computer, workstation, telephone handset, television, and so on.
4. Transmission medium. The transmission medium is the physical
path by which a message travels from sender to receiver. Some
examples of transmission media include twisted-pair wire, coaxial
cable, fiber-optic cable, and radio waves.

9. 1.9
Figure 1.1 Five components of data communication
5. Protocol. A protocol is a set of rules that govern data communications. It
represents an agreement between the communicating devices. Without a
protocol, two devices may be connected but not communicating, just as a
person speaking French cannot be understood by a person who speaks only
Japanese.

10. 1.10
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)

11. 1.11
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)
Simplex
In simplex mode, the communication is unidirectional, as on a one-way
street. Only one of the two devices on a link can transmit; the other can only
receive (see Figure 1.2a).
Keyboards and traditional monitors are examples of simplex devices. The
keyboard can only introduce input; the monitor can only accept output. The
simplex mode can use the entire capacity of the channel to send data in one
direction.

12. 1.12
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)
Inhalf-duplexmode,eachstationcanbothtransmitandreceive,butnotatthesame
time.Whenonedeviceissending,theothercanonlyreceive,andviceversa(seeFigure
1.2b).Thehalf-duplexmodeislikeaone-laneroadwithtrafficallowedinboth
directions.
Whencarsaretravelinginonedirection,carsgoingtheotherwaymustwait.Inahalf-
duplextransmission,theentirecapacityofachannelistakenoverbywhicheverofthe
twodevicesistransmittingatthetime.Walkie-talkiesandCB(citizensband)radiosare
bothhalf-duplexsystems.
Thehalf-duplexmodeisusedincaseswherethereisnoneedforcommunication
inbothdirectionsatthesametime;theentirecapacityofthechannelcanbeutilizedfor
eachdirection.

13. 1.13
Figure 1.2 Data flow (simplex, half-duplex, and full-duplex)
Infull-duplexmode(alsocalledduplex),bothstationscantransmitandreceive
simultaneously(seeFigure1.2c).
Thefull-duplexmodeislikeatwo-waystreetwithtrafficflowinginbothdirections
atthesametime.Infull-duplexmode,signalsgoinginonedirectionsharethe
capacityofthelinkwithsignalsgoingintheotherdirection.Thissharingcanoccurin
twoways:Eitherthelinkmustcontaintwophysicallyseparatetransmissionpaths,
oneforsendingandtheotherforreceiving;orthecapacityofthechannelisdivided
betweensignalstravelinginbothdirections.
Onecommonexampleoffull-duplexcommunicationisthetelephonenetwork.
Whentwopeoplearecommunicatingbyatelephoneline,bothcantalkandlistenat
thesametime.Thefull-duplexmodeisusedwhencommunicationinbothdirectionsis
requiredallthetime.Thecapacityofthechannel,however,mustbedividedbetween
thetwodirections.

14. 1.14
1-2 NETWORKS
Anetworkisasetofdevices(oftenreferredtoasnodes)
connectedbycommunicationlinks.Anodecanbea
computer,printer,oranyotherdevicecapableofsending
and/orreceivingdatageneratedbyothernodesonthe
network.
Distributed Processing
Network Criteria
Physical Structures
Network Models
Categories of Networks
Interconnection of Networks: Internetwork
Topics discussed in this section:

15. 1.15
NetworkCriteria
Anetworkmustbeabletomeetacertainnumberofcriteria.Themostimportantoftheseare
performance,reliability,andsecurity.
Performance
Performancecanbemeasuredinmanyways,includingtransittimeandresponsetime.
Transittimeistheamountoftimerequiredforamessagetotravelfromonedevicetoanother.
Responsetimeistheelapsedtimebetweenaninquiryandaresponse.Theperformance
ofanetworkdependsonanumberoffactors,includingthenumberofusers,thetypeof
transmissionmedium,thecapabilitiesoftheconnectedhardware,andtheefficiencyofthe
software.
Performanceisoftenevaluatedbytwonetworkingmetrics:throughputanddelay.Weoftenneed
morethroughputandlessdelay.However,thesetwocriteriaareoftencontradictory.Ifwetryto
sendmoredatatothenetwork,wemayincreasethroughputbutweincreasethedelaybecause
oftrafficcongestioninthenetwork.
Reliability
Inadditiontoaccuracyofdelivery,networkreliabilityismeasuredbythefrequencyoffailure,the
timeittakesalinktorecoverfromafailure,andthenetwork’srobustnessinacatastrophe.
Security
Networksecurityissuesincludeprotectingdatafromunauthorizedaccess,protectingdatafrom
damageanddevelopment,andimplementingpoliciesandproceduresforrecoveryfrombreaches
anddatalosses.

16. 1.16
Figure 1.3 Types of connections: point-to-point and multipoint

17. 1.17
Figure 1.3 Types of connections: point-to-point and multipoint
Apoint-to-pointconnectionprovidesadedicatedlinkbetweentwo
devices.Theentirecapacityofthelinkisreservedfortransmission
betweenthosetwodevices.Mostpoint-to-pointconnectionsusean
actuallengthofwireorcabletoconnectthetwoends,butotheroptions,
suchasmicrowaveorsatellitelinks,arealsopossible(seeFigure1.3a).
Whenwechangetelevisionchannelsbyinfraredremotecontrol,weare
establishingapoint-to-pointconnectionbetweentheremotecontroland
thetelevision’scontrolsystem.

18. 1.18
Figure 1.3 Types of connections: point-to-point and multipoint
A multipoint (also called multidrop) connection is one in which more
than two specific devices share a single link.
In a multipoint environment, the capacity of the channel is shared, either
spatially or temporally. If several devices can use the link
simultaneously, it is a spatially shared connection. If users must take
turns, it is a timeshared connection.

19. 1.19
Figure 1.4 Categories of topology

20. 1.20
Figure 1.5 A fully connected mesh topology (five devices)

21. 1.21
Inameshtopology,everydevicehasadedicatedpoint-to-pointlinkto
everyotherdevice.Thetermdedicatedmeansthatthelinkcarriestraffic
onlybetweenthetwodevicesitconnects.Tofindthenumberofphysical
linksinafullyconnectedmeshnetworkwithnnodes,wefirstconsider
thateachnodemustbeconnectedtoeveryothernode.Node1mustbe
connectedton–1nodes,node2mustbeconnectedton–1
nodes,andfinallynodenmustbeconnectedton–1nodes.Weneedn
(n–1)physicallinks.However,ifeachphysicallinkallows
communicationinbothdirections(duplexmode),wecandividethe
numberoflinksby2.Inotherwords,wecansaythatinamesh
topology,weneedn(n–1)/2duplex-modelinks.Toaccommodatethat
manylinks,everydeviceonthenetworkmusthaven–1input/output
(I/O)ports(seeFigure1.4)tobeconnectedtotheothern–1stations.

22. 1.22
Ameshoffersseveraladvantagesoverothernetworktopologies.
•First,theuseofdedicatedlinksguaranteesthateachconnectioncan
carryitsowndataload,thuseliminatingthetrafficproblemsthatcan
occurwhenlinksmustbesharedbymultipledevices.
•Second,ameshtopologyisrobust.Ifonelinkbecomesunusable,it
doesnotincapacitatetheentiresystem.
•Third,thereistheadvantageofprivacyorsecurity.Whenevery
messagetravelsalongadedicatedline,onlytheintendedrecipient
seesit.Physicalboundariespreventotherusersfromgainingaccess
tomessages.
•Finally,point-to-pointlinksmakefaultidentificationandfaultisolation
easy.Trafficcanberoutedtoavoidlinkswithsuspectedproblems.
Thisfacilityenablesthenetworkmanagertodiscovertheprecise
locationofthefaultandaidsinfindingitscauseandsolution.

23. 1.23
Figure 1.6 A star topology connecting four stations

24. 1.24
Inastartopology,eachdevicehasadedicatedpoint-to-pointlinkonlyto
acentralcontroller,usuallycalledahub.Thedevicesarenotdirectly
linkedtooneanother.Unlikeameshtopology,astartopologydoesnot
allowdirecttrafficbetweendevices.Thecontrolleractsasanexchange:
Ifonedevicewantstosenddatatoanother,itsendsthedatatothe
controller,whichthenrelaysthedatatotheotherconnecteddevice.star
topologyislessexpensivethanameshtopology.Inastar,eachdevice
needsonlyonelinkandoneI/Oporttoconnectittoanynumberof
others.Thisfactoralsomakesiteasytoinstallandreconfigure.

25. 1.25
Farlesscablingneedstobehoused,andadditions,moves,and
deletionsinvolveonlyoneconnection:betweenthatdeviceandthehub.
Otheradvantagesincluderobustness.Ifonelinkfails,onlythatlinkis
affected.Allotherlinksremainactive.Thisfactoralsolendsitselfto
easyfaultidentificationandfaultisolation.Aslongasthehubisworking,
itcanbeusedtomonitorlinkproblemsandbypassdefectivelinks.One
bigdisadvantageofastartopologyisthedependencyofthewhole
topologyononesinglepoint,thehub.Ifthehubgoesdown,thewhole
systemisdead.Althoughastarrequiresfarlesscablethanamesh,
eachnodemustbelinkedtoacentralhub.Forthisreason,oftenmore
cablingisrequiredinastarthaninsomeothertopologies(suchasring
orbus).

26. 1.26
Figure 1.7 A bus topology connecting three stations
Theprecedingexamplesalldescribepoint-to-point
connections.Abustopology,ontheotherhand,is
multipoint.
Onelongcableactsasabackbonetolinkallthe
devicesinanetwork

27. 1.27
Nodes are connected to the bus cable by drop lines and taps. A drop
line is a connection running between the device and the main cable. A
tap is a connector that either splices into the main cable or punctures
the sheathing of a cable to create a contact with the metallic core. As a
signal travels along the backbone, some of its energy is transformed
into heat. Therefore, it becomes weaker and weaker as it travels farther
and farther.
For this reason there is a limit on the number of taps a bus can support
and on the distance between those taps.

28. 1.
Advantagesofabustopologyincludeeaseofinstallation.Backbone
cablecanbelaidalongthemostefficientpath,thenconnectedtothe
nodesbydroplinesofvariouslengths.Inthisway,abususesless
cablingthanmeshorstartopologies.Inastar,forexample,four
networkdevicesinthesameroomrequirefourlengthsofcable
reachingallthewaytothehub.Inabus,thisredundancyiseliminated.
Onlythebackbonecablestretchesthroughtheentirefacility.Each
droplinehastoreachonlyasfarasthenearestpointonthe
backbone.
Disadvantagesincludedifficultreconnectionandfaultisolation.Abus
isusuallydesignedtobeoptimallyefficientatinstallation.Itcan
thereforebedifficulttoaddnewdevices.Signalreflectionatthetaps
cancausedegradationinquality.Thisdegradationcanbecontrolled
bylimitingthenumberandspacingofdevicesconnectedtoagiven
lengthofcable.Addingnewdevicesmaythereforerequiremodification
orreplacementofthebackbone.
Inaddition,afaultorbreakinthebuscablestopsalltransmission,
evenbetweendevicesonthesamesideoftheproblem.Thedamaged
areareflectssignalsbackinthedirectionoforigin,creatingnoisein
bothdirections.Bustopologywastheoneofthefirsttopologies

29. 1.29
Figure 1.8 A ring topology connecting six stations
Inaringtopology,eachdevicehasadedicatedpoint-to-pointconnectionwith
onlythetwodevicesoneithersideofit.Asignalispassedalongtheringin
onedirection,fromdevicetodevice,untilitreachesitsdestination.Each
deviceintheringincorporatesarepeater.Whenadevicereceivesasignal
intendedforanotherdevice,itsrepeaterregeneratesthebitsandpasses
themalong

30. 1.30
Figure 1.9 A hybrid topology: a star backbone with three bus networks

31. 1.31
Figure 1.10 An isolated LAN connecting 12 computers to a hub in a closet

32. 1.32
Figure 1.11 WANs: a switched WAN and a point-to-point WAN

33. 1.33
Figure 1.12 A heterogeneous network made of four WANs and two LANs

34. 1.34
1-3 NETWORK TYPES
Afterdefiningnetworksintheprevioussectionand
discussingtheirphysicalstructures,weneedtodiscuss
differenttypesofnetworksweencounterintheworld
today.Thecriteriaofdistinguishingonetypeofnetwork
fromanotherisdifficultandsometimesconfusing.
Weuseafewcriteriasuchassize,geographicalcoverage,
andownershiptomakethisdistinction.Afterdiscussing
twotypesofnetworks,LANsandWANs,wedefine
switching,whichisusedtoconnectnetworkstoforman
internetwork(anetworkofnetworks).

35. 1.35
Alocalareanetwork(LAN)isusuallyprivatelyownedandconnects
somehostsinasingleoffice,building,orcampus.Dependingonthe
needsofanorganization,aLANcanbeassimpleastwoPCsanda
printerinsomeone’shomeoffice,oritcanextendthroughouta
companyandincludeaudioandvideodevices.EachhostinaLANhas
anidentifier,anaddress,thatuniquelydefinesthehostintheLAN.A
packetsentbyahosttoanotherhostcarriesboththesourcehost’sand
thedestinationhost’saddresses.Inthepast,allhostsinanetworkwere
connectedthroughacommoncable,whichmeantthatapacketsent
fromonehosttoanotherwasreceivedbyallhosts.Theintended
recipientkeptthepacket;theothersdroppedthepacket.Today,most
LANsuseasmartconnectingswitch,whichisabletorecognizethe
destinationaddressofthepacketandguidethepackettoitsdestination
withoutsendingittoallotherhosts.Theswitchalleviatesthetrafficin
theLANandallowsmorethanonepairtocommunicatewitheachother
atthesametimeifthereisnocommonsourceanddestinationamong
them.NotethattheabovedefinitionofaLANdoesnotdefinethe
minimumormaximumnumberofhostsinaLAN.Figure1.8showsa
LANusingeitheracommoncableoraswitch.
Local Area Network

36. 1.36
Wide Area Network
Awideareanetwork(WAN)isalsoaninterconnectionof
devicescapableofcommunication.However,therearesome
differencesbetweenaLANandaWAN.ALANisnormally
limitedinsize,spanninganoffice,abuilding,oracampus;a
WANhasawidergeographicalspan,spanningatown,astate,a
country,oreventheworld.ALANinterconnectshosts;
aWANinterconnectsconnectingdevicessuchasswitches,
routers,ormodems.ALANisnormallyprivatelyownedbythe
organizationthatusesit;aWANisnormallycreatedandrunby
communicationcompaniesandleasedbyanorganizationthat
usesit.WeseetwodistinctexamplesofWANstoday:point-to-
pointWANsandswitchedWANs.

37. 1.37
1-3 THE INTERNET
TheInternethasrevolutionizedmanyaspectsofourdaily
lives.Ithasaffectedthewaywedobusinessaswellasthe
waywespendourleisuretime.TheInternetisa
communicationsystemthathasbroughtawealthof
informationtoourfingertipsandorganizeditforouruse.
A Brief History
The Internet Today (ISPs)
Topics discussed in this section:

38. 1.38
Figure 1.13 Hierarchical organization of the Internet