Data+Communication+and+Networking

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JUNE 2005 DATA COMMUNICATION AND NETWORKING

DATA COMMUNICATION ANDDATA COMMUNICATION AND NETWORKING NETWORKING

DATA COMMUNICATION ANDDATA COMMUNICATION AND NETWORKING NETWORKING

CHAPTER 1 - PRELIM


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JUNE 2005 DATA COMMUNICATION AND NETWORING

DATA COMMUNICATIONS

Is the exchange of databetween two devices via someform of transmission mediumsuch as a wire cable.


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1. Delivery . The system mustdeliver data to the correctdestination.

2 . Accuracy . The system mustdeliver the data accurately

3 . Timeliness . The system mustdeliver data in a timelymanner.

3 Fundamental Characteristics:


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Components

1. Message . Is the information(data) to be communicated.

2 . Sender . Is the device thatsends the data message.

3 . Receiver . Is the device thatreceives the message.


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4 . Medium . Is the physical pathby which a message travelsfrom the sender to receiver.

5 . P rotocol . Is a set of rulesthat govern datacommunications. It

represents an agreementbetween the communicatingdevices.


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Direction of Data FlowTransmission Modes

1. Simplex Mode , the communication isunidirectional. Only one of the twodevices on a link can transmit; theother can only receive.

2 . H alf-Duplex , each station can bothtransmit and receive, but not atthe same time.

3 . Full-Duplex (also called duplex ),both stations can transmit andreceive simultaneously.


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NETWORKS

Is a set of devices (oftenreferred to as nodes ) connected

by communication links.


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Distributed P rocessing

In which task is divided amongmultiple computers. Instead ofa single large machine beingresponsible for all aspects ofa process , separate computers

(usually a PC or workstation)handle a subset.


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Network Criteria1. P erformance can be measured in many

ways, including transit time and

response time. The performance of anetwork depends on a number offactors,

Number of users

Type of transmission mediumCapabilities of the connected hardware

Efficiency of the software


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P hysical StructuresL ine Configuration

A network is two or more devices

connected together through Links.

Link is a communications pathwaythat transfers data from onedevice to another.


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There are two possible type ofconnections/line configurations:

1. P oint-to-point , connectionprovides a dedicated linkbetween two devices. The entirecapacity of the link isreserved for transmissionbetween those two devices.


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2 . Multipoint (also called multidrop )connection is one in

which more than two specificdevices share a single link.

The capacity of the channel is

shared, either spatially ortemporally ( timeshare ).


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P hysical TopologyRefers to the way in which a networkis laid out physically. Two or moredevices connect to a link; two or morelinks form a topology.

Is the geometric representation of therelationship of all the links andlinking devices (usually called nodes)to one another.


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Four Basic Topologies:1. Mesh . Every device has a

dedicated point-to-point linkto every other device. A fullyconnected mesh network has n(n-1)/2 physical channels to linkn devices. Every device on thenetwork must have n-1input/output (I/O) ports.


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Advantages of Mesh:a) Eliminates the traffic problems that

can occur when links must be shared

by multiple devices.b) Robust. If one link becomesunusable, it does not incapacitatethe entire system.

c) Privacy or Securityd) Makes fault identification and fault

isolation easy. Traffic can routedto avoid links with suspectedproblems.


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Disadvantages of Mesh:a) Because every device must be

connected to every other device,

installation and reconfiguration aredifficult.b) The sheer bulk of the wiring can be

greater than the available space (inwalls, ceilings, or floors) can

accommodate.c) The hardware required to connect

each link (I/O ports and cable) canbe prohibitively expensive.


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2 . Star . A topology in which eachdevice has a dedicated point-to-point link only to a centralcontroller, usually called a hub .The controller acts as anexchange: if one device wants tosend data to another, it sendsthe data to the controller, whichthen relays the data to the otherconnected device.


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Advantages of Star:a) Less expensive than a mesh topology.b) Each device needs only one link and

one I/O port to connect it to anynumber of others. Thus, make it easyto install and reconfigure.

c) Less cabling needs to be housed, andadditions, moves, and deletionsinvolve only one connection: betweenthat device and the hub.

d) Robustnesse) Easy fault identification and fault

isolation.


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Disadvantages of Star:Each node must be linked to a

central hub. F or these reason morecabling is required in a star thanin some other topologies (such astree, ring, or bus).


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3 . Bus . A network topology in whichall computers are attached to ashared medium (often a singlecable). One long cable acts as abackbo ne to link all the devicesin the network. Nodes are

connected to the bus cable bydrop lines and taps. Bus topologyis multipoint.


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A dr op li ne is a connection runningbetween the device and the maincable. A t ap is a connector thateither splices into the main cableor punctures the sheathing of acable to create a contact with the

metallic core.


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Advantages of Bus:a) Ease of installation.

b) Use less cabling than mesh, orstar topologies.


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Disadvantages of Bus:a) Difficult reconfiguration and fault

isolation.

b) A fault or break in the bus cablestops all transmission, even betweendevices on the same side of the

problem. The damage area reflectssignals back in the direction oforigin, creating noise in bothdirections.


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4 . Ring . Each device has a dedicatedpoint-to-point connection onlywith the two devices on eitherside of it. A signal is passedalong the ring in one direction,from device to device, until it

reaches its destination. Eachdevice in the ring incorporates arepeater.


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Advantages of Ring:a) Easy to install and

reconfigure.b) F ault isolation is simplified.


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Disadvantages of Ring:a) Unidirectional traffic.

b) A break in the ring (such asdisabled station) can disablethe entire network. Thisweakness can be solved by usingd ual r i ng o r a swi t ch capableof closing off the break.


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Categories of NetworksSize Ownership Distance it

covers

LAN F ewkilometers,licensingrestrictionson the # ofusers per copyof software oraccess of OS

Privately owned Links devicesin a singleoffice buildingor campus

2 PCs & aprinter, in ahouse oroffice, 4 TO16 Mbps rangeup to 100Mbps, voice,sound, &videoperipherals,Bus, Ring, &star

MAN 3 to 30 miles Maybe whollyowned andoperated by aprivate company,or it maybeservice providedby a publiccompany, such asa local telephonecompany.

Entire city,may be a singlenetwork such ascable TVnetwork, LAN toLAN (co. use aMAN to connectthe LANs in allofficesthroughout thecity


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Categories of Networks

Size Ownership Distance itcovers

WAN Unlimited # ofmiles

Public leasedthrough AT&T,

MCI, SPRINTor privatecommunicationdevices orcombination

Largegeographical

areas(country,continent,whole world

Data, voice,image & video

information.


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The Internet A BriefH istory

An i nte r net (note the lowercaseletter i) is two or more networks

that can communicate with eachother. The most notable internet iscalled the Inte r net (uppercaseletter I), a collaboration of more

than hundreds of thousandsinterconnected networks.


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Milestones Mid- 1960 s

Mainframe computers in research organizationswere stand-alone devices.ARPA in the DOD

1967ACM meeting ARPA presented its ideas forARPANETinterface message processor (IMP).

1969

ARPANET was a reality.F our nodes: UCLA, UCSB, SRI, University ofUtahNetwork Control Protocol (NCP)


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Milestones

197 2Vint Cerf and Bob Kahn collaborated onInternetting P roject1973 paper outlined the protocols to achieve

end-to-end delivery of packets.Paper on TCP included concepts such asencapsulation, the datagram, and the functionsof a gateway.

TCP split into two protocols: TC P and I PIP would handle datagram routingTC P would be responsible for higher-levelfunctions such as segmentation, reassembly,and error detection. The internetworkingprotocol became known as TCP/IP.


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P ROTOCOLS AND STANDARDSP rotocolIs a set of rules that govern datacommunication. F or communication to

occur they must agree on a protocol.A protocol defines what, how, when itis communicated. The key elements ofa protocol are syntax, semantics, andtiming.


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Key Elements of a P rotocol

1. Syntax refers to the structure orformat of the data, meaning the

order in which they are presented.2 . Semantics refers to the meaning of

each section of bits. How aparticular pattern to be

interpreted, and what action is tobe taken based on thatinterpretation?


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Key Elements of a P rotocol

3 . Timing refers to twocharacteristics: when datashould be sent and how fastthey can be sent.


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Standards

Standards are essential increating and maintaining an openand competitive market.

They provide guidelines tomanufacturers, vendors,government agencies, and otherservice providers to ensure the

kind of interconnectivity.


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Categories of Standards

1. De facto (by fact) . Standardsthat have not been approved by

an organized body but have beenadopted as standards throughwidespread use.

2 . De jure (by law) . Those thathave been legislated by anofficially recognized body.


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Standard Organizations

Standards are develop throughthe cooperation of standards

creation committees, forums, andgovernment regulatory agencies.


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Standard Creation Committees

International Organization forStandardization (ISO)

Multinational bodyCreated in 1947

OSIInternational Telecommunication Union-Telecommunication Standards (ITU-T)

Consultative Committee for InternationalTelegraphy and Telephony (CCITT)Best known standards are V series: definetransmission over public digital networks, and Xseries: define transmission over public digitalnetworks.


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American National Standards Institute (ANSI)U.S. voting representative to both ISO and ITU-T.Members include professional societies, industry

associations, governmental and regulatory bodies,

and consumer groups.Institute of Electrical and ElectronicsEngineers (IEEE)

Largest national professional group involved indeveloping standards for computing, communication,electrical engineering, and electronics.Sponsored an important standard for LAN calledProject 802 (e.g. 802.3, 802.4, 802.5)


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Electronic Industries Association (EIA)An association of electronic manufacturers in theU.S.Responsible for developing the EIA-232-D, EIA-449,and EIA-530 define serial transmission betweentwo digital devices (e.g. computer to modem)


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Forums

Telecommunications technologydevelopment is moving faster thanthe ability of standardcommittees to ratify standards.F orums consist of representativesfrom corporations, they work withuniversities, and users thattest, evaluate, and standardizenew technologies.


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Regulatory AgenciesAll communications technology issubject to regulation by governmentagencies such as the F e d e r alC ommu n ica t io n s C ommissio n ( F CC ) in theUnited States. The purpose of theseagencies is to protect the publicinterest by regulating radio,television, and wire/cablecommunications.

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