1_Chapter_01 fgccxcdddr rama khal net wo.pdf

ومع ذلك، بالنسبة لمثال فضاء الحالة الخاص بنا، سنستخدم نموذجًا مختلفًا قليلاً. لا تزال نفس المعادلة الخاصة بالكرة سارية، ولكن بدلاً من التحكم في موضعها من خلال زاوية المحرك (θ)، سنتحكم في عزم الدوران المطبق على العارضة مباشرةً. وفيما يلي تمثيل هذا النظام:

1. EET414 Computer Networks
Faculty of Electrical and Electronic Engineering
Department of Control Engineering and Automation
Dr Rami Khal

2. Chapter 1
Introduction

3. Chapter 1: Outline
1.1DataCommunications
1.2Networks
1.3NetworkTypes
1.4InternetHistory
1.5ProtocolsandStandards

4. Chapter 1: Objective
Thefirstsectionintroducesdatacommunicationsand
definestheircomponentsandthetypesofdataexchanged.
Italsoshowshowdifferenttypesofdataarerepresented
andhowdataisflowedthroughthenetwork.
Thesecondsectionintroducesnetworksanddefinestheir
criteriaandstructures.Itintroducesfourdifferent
networktopologiesthatareencounteredthroughoutthe
book.
Thethirdsectiondiscussesdifferenttypesofnetworks:
LANs,WANs,andinternetworks(internets).Italso
introducestheInternet,thelargestinternetintheworld.
Theconceptofswitchingisalsointroducedinthissection
toshowhowsmallnetworkscanbecombinedtocreate
largerones.

5. Chapter 1: Objective (continued)
ThefourthsectioncoversabriefhistoryoftheInternet.
Thesectionisdividedintothreeeras:earlyhistory,the
birthoftheInternet,andtheissuesrelatedtotheInternet
today.Thissectioncanbeskippedifthereaderisfamiliar
withthishistory.
ThefifthsectioncoversProtocols,standardsandstandard
organizations.ThesectioncoversInternetstandardsand
Internetadministration.Werefertothesestandardsand
organizationsthroughoutthebook.

6. 1.6
1-1 DATA COMMUNICATIONS
Whenwecommunicate,wearesharing
information.Thissharingcanbelocalor
remote.Thetermtelecommunication,
whichincludestelephony,telegraph,
andtelevision,meanscommunicationat
adistance.
Datacommunicationsarethe
exchangeofdatabetweentwodevices
viasomeformoftransmissionmedia.

7. 1.7
1.1.1 Components
•Message:
–The information (data) to be communicated. Popular forms of information
include text, numbers, pictures, audio, and video.
•Sender:
–The device that sends the data message.
–It can be a computer, workstation, telephone handset, video camera, and so
on.
•Receiver:
–The device that receives the data message.
•Transmission medium:
–The physical path by which a message travels from sender to receiver.
–e.g., twisted-pair wire, coaxial cable, fiber-optic cable, and radio waves.
•Protocol:
–A set of rules that govern data communications.
–It represents an agreement between the communication devices.

8. 1.8
Figure 1.1: Five components of data communication

9. 1.9
1.1.2 Data Representation
Informationtodaycomesindifferentformssuch
astext,numbers,images,audio,andvideo.

10. 1.10
1.1.3 Data Flow
•Communication between two devices can be
simplex, half-duplex, or full-duplex (as shown in
next slide).
•Simplex
–The communication is unidirectional, as on a one-way
street.
•Half-duplex
–Each station can both transmit and receive, but not at
the same time.
•Full-duplex
–Both stations can transmit and receive simultaneously.

11. 1.11
Figure 1.2: Data flow

12. 1.12
1-2 NETWORKS
Anetworkistheinterconnectionofasetof
devicescapableofcommunication.Inthis
definition,adevicecanbeahostsuchasa
largecomputer,desktop,laptop,workstation,
cellularphone,orsecuritysystem.Adevicein
thisdefinitioncanalsobeaconnectingdevice
suchasarouteraswitch,amodemthat
changestheformofdata,andsoon.

13. 1.13
1.2.1 Network Criteria
Anetworkmustbeabletomeetacertainnumber
ofcriteria.Themostimportantoftheseare
performance,reliability,andsecurity.

14. 1.14
1.2.2 Physical Structures
Beforediscussingnetworks,weneedtodefine
somenetworkattributes.

15. 1.15
Figure 1.3: Types of connection

16. 1.16
Physical Topology
•The term physical topology refers to the way in which a
network is laid out physically.
•Two or more devices connectto a link; two or more links
form a topology.
•The topology of a network is the geometric representation
of the relationship of all the links and linking devices
(usually called nodes) to one another.
•Four basic topologies
–Mesh
–Star
–Bus
–Ring

17. 1.17
Mesh Topology
•Several advantages
–The use of dedicated links
–A mesh topology is robust
–The advantage of privacy or security
–Point-to-point links make fault identification and fault isolation easy
•Main disadvantages
–The amount of cabling and the number of I/O ports required
–Because every device must be connected to every other device,
installation and reconnection are difficult.
–The sheer bulk of the wiring can be greater than the available space
(in walls, ceilings, or floors) can accommodate.
–The hardware required to connect each link (I/O ports and cable)
can be prohibitively expensive.

18. 1.18
Figure 1.4: A fully-connected mesh topology

19. 1.19
Star Topology
•Deach device has a dedicated point-to-point link only to a
central controller, usually called a hub.
•Not similar with mesh topology, if one device wants to send
data to another, it sends the data to the controller, which
then relays the data to the other connected device.
•Advantages
–A star topology is less expensivethan a mesh topology.
–Easy to install and reconfigure
–Far less cabling needs to be housed
–Robustness: If one link fails, only that link is affected.
•Disadvantage
–The dependency of the whole topology on one single point, the hub.
If the hub goes down, the whole system is dead.

20. 1.20
Figure 1.5: A star topology

21. 1.21
Bus Topology
•A bus topology, on the other hand, is multipoint.
•One long cable acts as a backboneto link all the devices in
a network.
•Advantages
–Ease of installation
–Backbone cable can be laid along the most efficient path, then
connected to the nodes by drop linesof various lengths.
•Disadvantages
–Difficult reconnection and fault isolation
–Signal reflection at the tapscan cause degradation in quality
–A fault or break in the bus cable stops all transmission, even
between devices on the same side of the problem. The damaged
area reflects signals back in the direction of origin, creating noise in
both directions.

22. 1.22
Figure 1.6: A bus topology

23. 1.23
Ring Topology
•Relatively easy to install and reconfigure
•Each device is linked to only its immediate neighbors
(either physicallyor logically).
•Advantages
–To add or delete a device requires changing only two connections.
–Fault isolation is simplified.
–A signal is circulating at all times. If one device does not receive a
signal within a specified period, it can issue an alarm.
•Disadvantages
–Unidirectional traffic
–In a simple ring, a break in the ring (such as a disable station) can
disable the entire network.
–This weakness (above) can be solved by using a dual ring or a
switch capable of closing off the break.

24. 1.24
Figure 1.7: A ring topology

25. 1.25
1-3 NETWORKS TYPES
Afterdefiningnetworksintheprevious
sectionanddiscussingtheirphysical
structures,weneedtodiscussdifferenttypes
ofnetworksweencounterintheworldtoday.
Thecriteriaofdistinguishingonetypeof
networkfromanotherisdifficultand
sometimesconfusing.Weuseafewcriteria
suchassize,geographicalcoverage,and
ownershiptomakethisdistinction.

26. 1.26
Categories of Networks
•Local area network (LAN)
–usually privately owned and links the devices in a single
office, building, or campus.
–A LAN can be as simple as two PCs and a printer in
someone’s home office.
•Wide area network (WAN)
–Long distance transmission of data, image, audio, and
video information over large geographic areas.
•Metropolitan area network (MAN)
–A network with a size between a LAN and a WAN

27. 1.27
1.3.1 Local Area Network
Alocalareanetwork(LAN)isusuallyprivately
ownedandconnectssomehostsinasingleoffice,
building,orcampus.Dependingontheneedsofan
organization,aLANcanbeassimpleastwoPCs
andaprinterinsomeone’shomeoffice,oritcan
extendthroughoutacompanyandincludeaudio
andvideodevices.EachhostinaLANhasan
identifier,anaddress,thatuniquelydefinesthe
hostintheLAN.Apacketsentbyahosttoanother
hostcarriesboththesourcehost’sandthe
destinationhost’saddresses.

28. 1.28
Figure 1.8: An Isolated LAN in the past and today

29. 1.29
1.3.2 Wide Area Network
Awideareanetwork(WAN)isalsoanconnection
ofdevicescapableofcommunication.However,
therearesomedifferencesbetweenaLANanda
WAN.ALANisnormallylimitedinsize;aWAN
hasawidergeographicalspan,spanningatown,a
state,acountry,oreventheworld.ALAN
interconnectshosts;aWANinterconnects
connectingdevicessuchasswitches,routers,or
modems.ALANisnormallyprivatelyownedby
theorganizationthatusesit;aWANisnormally
createdandrunbycommunicationcompaniesand
leasedbyanorganizationthatusesit.

30. 1.30
Figure 1.9: A Point-to-Point WAN

31. 1.31
Figure 1.10: A Switched WAN

32. 1.32
Figure 1.11: An internetwork made of two LANs and one WAN

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

34. 1.34
1.3.3 Switching
Aninternetisaswitchednetworkinwhicha
switchconnectsatleasttwolinkstogether.A
switchneedstoforwarddatafromanetworkto
anothernetworkwhenrequired.Thetwomost
commontypesofswitchednetworksarecircuit-
switchedandpacket-switchednetworks.We
discussbothnext.

35. 1.35
Figure 1.13:A circuit-switched network

36. 1.36
Figure 1.14: A packet-switched network

37. 1.37
1.3.4 The Internet
Aswediscussedbefore,aninternet(notethe
lowercasei)istwoormorenetworksthatcan
communicatewitheachother.Themostnotable
internetiscalledtheInternet(uppercaseI),andis
composedofthousandsofinterconnected
networks.

38. 1.38
1-4 INTERNET HISTORY
Nowthatwehavegivenanoverviewof
theInternetanditsprotocol,letusgivea
briefhistoryoftheInternet.Thisbrief
historymakesitclearhowtheInternet
hasevolvedfromaprivatenetworktoa
globaloneinlessthanfortyyears.

39. 1.39
1.4.1 Early History
Thereweresomecommunicationnetworks,such
astelegraphandtelephonenetworks,before1960.
Thesenetworksweresuitableforconstant-rate
communicationatthattime,whichmeansthat
afteraconnectionwasmadebetweentwousers,
theencodedmessage(telegraphy)orvoice
(telephony)couldbeexchanged.Acomputer
network,ontheotherhand,shouldbeableto
handleburstydata,whichmeansdatareceivedat
variableratesatdifferenttimes.Theworldneeded
towaitforthepacket-switchednetworktobe
invented.

40. 1.40
1.4.2 Birth of the Internet
In1972,VintCerfandBobKahn,bothofwhom
werepartofthecoreARPANETgroup,
collaboratedonwhattheycalledtheInternetting
Project.Theywantedtolinkdissimilarnetworks
sothatahostononenetworkcouldcommunicate
withahostonanother.Thereweremanyproblems
toovercome:diversepacketsizes,diverse
interfaces,anddiversetransmissionrates,aswell
asdifferingreliabilityrequirements.Cerfand
Kahndevisedtheideaofadevicecalledagateway
toserveastheintermediaryhardwaretotransfer
datafromonenetworktoanother.

41. 1.41
1.4.3 Internet Today
Today,wewitnessarapidgrowthbothinthe
infrastructureandnewapplications.TheInternet
todayisasetofpiernetworksthatprovideservices
tothewholeworld.WhathasmadetheInternetso
popularistheinventionofnewapplications.

42. 1.42
1-5 PROTOCOLS AND STANDARDS
Inthissection,wedefinetwowidelyusedterms:
protocolsandstandards.First,wedefineprotocol,
whichissynonymouswithrule.Thenwediscuss
standards,whichareagreed-uponrules.
Protocols
Standards
Topics discussed in this section:

43. 1.43
Protocols
•An entityis anything capable of sending or
receiving information.
•A protocol defines what is communicated, how it is
communicated, and when it is communicated.
•Syntax
–Refers to the structure or format of the data, meaning
the order in which they are presented.
•Semantics
–Refers to the meaning of each section of bits.
•Timing
–When data should be sent and how fast they can be sent.

44. 1.44
Standards
•De facto standards
–de factomeans “by fact” or “by convention”
•De jure standards
–De jure means “by law” or “by regulation”
•Standard organizations
–International Organization for Standardization (ISO)
–International Telecommunication Union-Telecommunication standards
sector (ITU-T)
•Consultative Committee for International Telegraphy and Telephony (CCITT)
–American National Standards Institute (ANSI)
–Institute of Electrical and Electronics Engineers (IEEE)
–Electronic Industries Association (EIA)
•Government agencies
–Federal Communications Commission (FCC)
•Internet Standards
–Internet draft
–Request for Comment (RFC)