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OSI & TCP/IPOSI & TCP/IP

Reference ModelReference Model

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What is networking?What is networking?

An interconnection ofAn interconnection ofcomputers and othercomputers and otherdevices:devices: PrintersPrinters

Servers (computers)Servers (computers)

ScannersScanners

Network DevicesNetwork Devices HubsHubs

SwitchesSwitches RoutersRouters

FirewallFirewall

ModemModem

Wired and WirelessWired and Wireless

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Networking HistoryNetworking History

Standalone Device.Standalone Device.

Duplication of equipments and resources.Duplication of equipments and resources.

Inability to communicate efficiently.Inability to communicate efficiently.

Lack of networking management.Lack of networking management.

LAN.LAN.

Connects devices that are close together.Connects devices that are close together.

WAN.WAN.

Interconnects LANs across a large area.Interconnects LANs across a large area.

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Analyzing network in layersAnalyzing network in layers

What is flowing ?

Data

What different forms flow ?Text, Graphic, Video ...

What rules govern flow ?

Standard, Protocol ...

Where does the flow occur ?

Cable, Atmosphere ...

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CommunicationCommunication

Transmission of information.Transmission of information.

Examples:Examples: Speaking.Speaking.

Smoke signal.Smoke signal. Body language.Body language.

Morse.Morse.

Telephone.Telephone.

Broadcast systems (radio, television).Broadcast systems (radio, television).

InternetInternet

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Communication processCommunication process

Source

AddressDestination

Address

Medium

Packets

Protocols

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Communication:Communication: HumanHumanconversationconversation

AddressAddress

Hello Mr.A, I am BHello Mr.A, I am B

MediaMedia

AtmosphereAtmosphere

ProtocolProtocol

LanguageLanguage

SpeedSpeed

HandshakingHandshaking

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Data CommunicationData Communication

AddressAddress

Source address, Destination addressSource address, Destination address

MediaMedia

Cable, Fiber, AtmosphereCable, Fiber, Atmosphere

ProtocolProtocol

FormatFormat

ProcedureProcedure

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ProtocolProtocol

Protocol is a set ofProtocol is a set ofrulesrules, or an, or anagreementagreement, that determines the, that determines theformatformatandand transmissiontransmission of data thatof data that

make communication on a networkmake communication on a networkmore efficient.more efficient.

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OSI MODELOSI MODEL

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Evolution of networkingEvolution of networkingstandardsstandards

SNA

TCP/IP DECNET

Proprietary

Interconnectio

n

Development

Simplification

StandardStandard

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OSI model developmentOSI model development

Researched and developed by theResearched and developed by the ISOISO --IInternationalnternational OOrganization forrganization for SStandardizations.tandardizations.

1977:1977: establish a subcommittee to develop aestablish a subcommittee to develop a

communications architecture.communications architecture. 1984:1984: publish ISOpublish ISO--7498, the7498, the OOpenpen SSystemystem

IInterconnection (OSI) reference model.nterconnection (OSI) reference model.

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OSI modelOSI model

The OSI modelThe OSI model: a framework within which: a framework within whichnetworking standards can be developed.networking standards can be developed.

It provided vendors with a set of standards thatIt provided vendors with a set of standards that

ensured greater compatibility andensured greater compatibility andinteroperability between the various types ofinteroperability between the various types ofnetwork technologies that were produced by thenetwork technologies that were produced by themany companies around the world.many companies around the world.

ProprietaryProprietary vs.vs. OpenOpen

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A layered modelA layered model

The communications functions areThe communications functions arepartitioned into a hierarchical set of layers.partitioned into a hierarchical set of layers.

Each layer performs a related subset of theEach layer performs a related subset of the

functions required to communicate.functions required to communicate. Each layer relies on the next lower layer toEach layer relies on the next lower layer to

perform more primitive functions andperform more primitive functions andprovides services to the next higher layer.provides services to the next higher layer.

The OSI Model dThe OSI Model define a set of layers and theefine a set of layers and theservices performed by each layerservices performed by each layer

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Why a layered model?Why a layered model?

Reduces complexity.Reduces complexity.

Standardizes interfaces.Standardizes interfaces.

Facilitates modular engineering.Facilitates modular engineering.

Ensures interoperable technology.Ensures interoperable technology.

Accelerates evolution.Accelerates evolution.

Simplifies teaching and learning.Simplifies teaching and learning.

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7 layers of the OSI reference7 layers of the OSI referencemodelmodel

Layer 7:Layer 7:AApplicationpplication

Layer 6:Layer 6: PPresentationresentation

Layer 5:Layer 5: SSessionession

Layer 4:Layer 4: TTransportransport

Layer 3:Layer 3: NNetworketwork Layer 2:Layer 2: DData Linkata Link

Layer 1:Layer 1: PPhysicalhysical

AllPeople Seem To NeedData Processing

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The physical layerThe physical layer

Transmission of an unstructured bit streamTransmission of an unstructured bit streamover a physical link between end systems.over a physical link between end systems.

Electrical, mechanical, procedural and functionalElectrical, mechanical, procedural and functional

specificationsspecifications Physical data ratePhysical data rate

DistancesDistances

Physical connectorPhysical connector

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The dataThe data--link layerlink layer

Provides for the reliable transfer of dataProvides for the reliable transfer of datacross a physical link.cross a physical link.

FramesFrames

Physical addressPhysical address Network topologyNetwork topology

Line disciplineLine discipline

SynchronizationSynchronization Error controlError control

Flow controlFlow control

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The network layerThe network layer

Provides connectivity and path selectionProvides connectivity and path selectionbetween two host systems that may bebetween two host systems that may belocated on geographically separatedlocated on geographically separated

networks.networks. PacketsPackets

Virtual circuitsVirtual circuits

Route, routing table, routing protocolRoute, routing table, routing protocol Logical addressLogical address

FragmentationFragmentation

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The transport layerThe transport layer

Provides reliable, transparent transfer ofProvides reliable, transparent transfer ofdata over networks.data over networks.

Segments, data stream, datagramSegments, data stream, datagram

Connection oriented and connectionlessConnection oriented and connectionless EndEnd--toto--end flow controlend flow control

Error detection and recoveryError detection and recovery

Segmentation & reassemblySegmentation & reassembly

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The session layerThe session layer

Establishes, manages, and terminatesEstablishes, manages, and terminatessessions between two communicating hosts.sessions between two communicating hosts.

SessionsSessions

DialogDialog ConversationsConversations

Data exchangeData exchange

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The application layerThe application layer

Is the OSI layer that is closest to the user; itIs the OSI layer that is closest to the user; itprovides network services to the usersprovides network services to the usersapplications.applications.

File transferFile transfer Electronic mailElectronic mail

Terminal accessTerminal access

Word processingWord processing Intended communication partnersIntended communication partners

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Encapsulation example:Encapsulation example: AirAir--mailmail

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Encapsulation example:Encapsulation example: EE--mailmail

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LayerLayer--toto--layer communicationslayer communications

Request services

Provide services

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PeerPeer--toto--peer communicationspeer communications

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ProtocolsProtocols

Is a formal set ofIs a formal set ofrulesrules andand conventionsconventions thatthatgoverns how computers exchangegoverns how computers exchangeinformation over a network medium.information over a network medium.

Implements the functions of one or more ofImplements the functions of one or more ofthe OSI layers.the OSI layers.

A communication protocol is concerned withA communication protocol is concerned with

exchanging data betweenexchanging data between two peer layerstwo peer layers.. Protocol Data Units (Protocol Data Units (PDUsPDUs) : Block of data) : Block of data

that a protocol exchange.that a protocol exchange.

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ReviewReview

OSI Reference Model.OSI Reference Model.

Function of 7 layers.Function of 7 layers.

Encapsulation process.Encapsulation process.

PeerPeer--toto--peer communications.peer communications.

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TCP/IP model developmentTCP/IP model development

The lateThe late--60s The Defense Advance Research60s The Defense Advance ResearchProjects Agency (DARPA) originallyProjects Agency (DARPA) originallydevelopeddeveloped Transmission ControlTransmission Control

Protocol/Internet ProtocolProtocol/Internet Protocol ((TCP/IPTCP/IP) to) tointerconnect various defense departmentinterconnect various defense departmentcomputer networks.computer networks.

The Internet, an International Wide Area

The Internet, an International Wide AreaNetwork, uses TCP/IP to connect networksNetwork, uses TCP/IP to connect networks

across the world.across the world.

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The network access layerThe network access layer

Concerned with all of the issues that an IPConcerned with all of the issues that an IPpacket requires to actually make thepacket requires to actually make thephysical link.physical link. All the details in the OSIAll the details in the OSI

physical and data link layersphysical and data link layers.. Electrical, mechanical, procedural and functionalElectrical, mechanical, procedural and functional

specifications.specifications.

Data rate, Distances, Physical connector.Data rate, Distances, Physical connector.

Frames, physical addressing.Frames, physical addressing.

Synchronization, flow control, error control.Synchronization, flow control, error control.

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The internet layerThe internet layer

Send source packets from any network onSend source packets from any network onthe internetwork and have them arrive atthe internetwork and have them arrive atthe destination independent of the path andthe destination independent of the path and

networks they took to get therenetworks they took to get there.. Packets, Logical addressing.Packets, Logical addressing.

Internet Protocol (IP).Internet Protocol (IP).

Route , routing table, routing protocol.Route , routing table, routing protocol.

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The transport layerThe transport layer

The transport layer deals with the qualityThe transport layer deals with the quality--ofof--service issues of reliability, flow control,service issues of reliability, flow control,and error correction.and error correction.

Segments, data stream, datagram.Segments, data stream, datagram. Connection oriented and connectionless.Connection oriented and connectionless.

Transmission control protocol (TCP).Transmission control protocol (TCP).

User datagram protocol (UDP).User datagram protocol (UDP). EndEnd--toto--end flow control.end flow control.

Error detection and recovery.Error detection and recovery.

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The application layerThe application layer

Handles highHandles high--level protocols, issues oflevel protocols, issues ofrepresentation, encoding, and dialogrepresentation, encoding, and dialogcontrol.control.

The TCP/IP combines all applicationThe TCP/IP combines all application--relatedrelatedissues into one layer, and assures this dataissues into one layer, and assures this datais properly packaged for the next layer.is properly packaged for the next layer.

FTP, H

TTP, SMNP, DNS ...F

TP, H

TTP, SMNP, DNS ...

Format of data, data structure, encode Format of data, data structure, encode

Dialog control, session management Dialog control, session management

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TCP/IP protocol stackTCP/IP protocol stack

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C i TCP/IP ith OSIC i TCP/IP ith OSI

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Comparing TCP/IP with OSIComparing TCP/IP with OSI(cont.)(cont.)

Differences:Differences: TCP/IP combines the presentation and sessionTCP/IP combines the presentation and session

layer issues into its application layer.layer issues into its application layer.

TCP/IP combines the OSI data link andTCP/IP combines the OSI data link andphysical layers into one layer.physical layers into one layer.

TCP/IP appears simpler because it has fewerTCP/IP appears simpler because it has fewerlayers.layers.

Typically networks aren't built on the OSITypically networks aren't built on the OSIprotocol, even though the OSI model is usedprotocol, even though the OSI model is usedas a guide.as a guide.

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Networking DevicesNetworking Devices

A bl t d ib thiA bl t d ib thi

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Are you able to describe thisAre you able to describe thisdiagram?diagram?

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LANDevicesLANDevices

Concept of Broadcast and Collisions.Concept of Broadcast and Collisions. Categorization based on OSI layers.Categorization based on OSI layers.

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BroadcastBroadcast

Each host on the LAN sends its data (orEach host on the LAN sends its data (orbroadcasts its data) to every other host.broadcasts its data) to every other host.

FirstFirst--come, firstcome, first--serve.serve.

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CollisionCollision

If more than one node attempts toIf more than one node attempts totransmit at the same timetransmit at the same time

Packets destroyed, bit by bitPackets destroyed, bit by bit

Two devices trying to occupy the sameTwo devices trying to occupy the samemedium (wire) at the same timemedium (wire) at the same time

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HostsHosts

Computer Server

Printer

NICNIC

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5151

LANDevice:LANDevice: TransceiverTransceiver

Connect different media technologies.Connect different media technologies.

Layer 1 device.Layer 1 device.

UTP

BNC

AUI

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LANDevice:LANDevice: RepeaterRepeater

Regenerates and repeats the signal.Regenerates and repeats the signal.

Layer 1 device.Layer 1 device.

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LANDevice:LANDevice: HubHub

A multiA multi--port repeater.port repeater.

Layer 1 device.Layer 1 device.

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OSIReview:OSIReview: Layer 2Layer 2

Responsibility:Responsibility:

Provides for the reliable transfer of data cross aProvides for the reliable transfer of data cross a

physical link.physical link. Concerned:Concerned:

Frames.Frames.

Physical address (HW or MAC):Physical address (HW or MAC): FlatFlat..

Line discipline.Line discipline. Error and flow control.Error and flow control.

SegmentSegment..

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5555

LANDevice:LANDevice: NICNIC

Network interface of hosts.Network interface of hosts.

BuildBuild--in physical address.in physical address.

Layer 2 device.Layer 2 device.

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LANDevice:LANDevice: BridgeBridge

Keeps traffic local by filtering traffic basedKeeps traffic local by filtering traffic basedon physical addresses.on physical addresses.

Layer 2 device.Layer 2 device.

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LANDevice:LANDevice: SwitchSwitch

A multiA multi--port bridge.port bridge.

Layer 2 device.Layer 2 device.

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OSIReview:OSIReview: Layer 3Layer 3

Responsibility:Responsibility:

ConnectionConnection andand path selectionpath selection between two endbetween two end

system across networks.system across networks. Concerned:Concerned:

Packets.Packets.

Logical address:Logical address: HierarchicalHierarchical..

Networks and Hosts addressing.Networks and Hosts addressing. Route , Routing table, Routing protocol.Route , Routing table, Routing protocol.

NetworkNetwork..

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WANDevice:WANDevice: Router FunctionsRouter Functions

Path determinationPath determination::

The process of evaluating a packetsThe process of evaluating a packets

destination IP address so that the router candestination IP address so that the router candecide which port to send out the packet.decide which port to send out the packet.

Packet switchingPacket switching::

The router reThe router re--encapsulates the packet in theencapsulates the packet in theprotocol needed for the specified port and thenprotocol needed for the specified port and thenswitches the packet out that port.switches the packet out that port.

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WANDevice:WANDevice: CloudCloud

Another networkAnother network

Include layer 1Include layer 1 7 devices7 devices

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Devices function at LayersDevices function at Layers

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Twisted Pair CablingTwisted Pair Cabling

Shielded Twisted PairShielded Twisted Pair

Provides resistance toProvides resistance to

EMI and radioEMI and radiofrequencyfrequency

Cancellation andCancellation andtwisting of wires,twisting of wires,shieldingshielding

More expensiveMore expensive

Cable length 100mCable length 100m

Unshielded twistedUnshielded twisted--pairpair relies on cancellationrelies on cancellation

effecteffect

number of twistsnumber of twistsvariesvaries

Less expensiveLess expensive

Cable length 100mCable length 100m Fastest copper basedFastest copper based

media todaymedia today

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6666

COAXIALCABLECOAXIALCABLE

Copper conductor in centerCopper conductor in center

Flexible insulationFlexible insulation

Metallic foil or copper braid acts as second wireMetallic foil or copper braid acts as second wirein circuitin circuit

Max. length 500mMax. length 500m Thicker than Twisted pair, more difficult to workThicker than Twisted pair, more difficult to work

withwith

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Each media has advantages andEach media has advantages and

disadvantages:disadvantages: Cable lengthCable length

CostCost

Ease of installationEase of installation Susceptibility to interferenceSusceptibility to interference

The most common isThe most common is Category 5Category 5

UTPUTP cablecable 802.3z802.3z Gigabit Ethernet over FiberGigabit Ethernet over Fiber

802.3ab802.3ab Gigabit Ethernet over UTPGigabit Ethernet over UTP

Cabling the LANCabling the LAN

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EthernetEthernet is the most widely used LANis the most widely used LANtechnologytechnology

first implemented by thefirst implemented by the DIXDIX groupgroup

Used as basis forUsed as basis for IEEE802.3IEEE802.3specificationspecification

802.3u802.3u Fast EthernetFast Ethernet

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Ethernet technologies can be used in a campusEthernet technologies can be used in a campus

network in several different ways:network in several different ways: 10 Mbps10 Mbps at theat the user leveluser level to provide goodto provide good

performance.performance.

100 Mbps100 Mbps for clients orfor clients or serversservers that require morethat require more

bandwidth.bandwidth. Fast or Gigabit Ethernet betweenFast or Gigabit Ethernet between backbonebackbone

devices.devices.

EthernetEthernet

TIA/EIA STANDARDSTIA/EIA STANDARDS

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7171

TIA/EIASTANDARDSTIA/EIASTANDARDS

Horizontal cablingHorizontal cabling

telecommunications closetstelecommunications closets

backbone cablingbackbone cabling

equipment roomsequipment rooms

work areaswork areas

entrance facilitiesentrance facilities

C bliC bli

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CablingCabling

Crossover CableCrossover Cable -- used to connect oneused to connect onedevice to anotherdevice to another

Straight throughStraight through -- used to connect to hubused to connect to hubor patch panelor patch panel

Rollover or console cableRollover or console cable -- used toused to

connect a PC to the router for purposesconnect a PC to the router for purposesof accessing the routerof accessing the router

UTP implementationUTP implementation

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UTP implementationUTP implementation EIA/TIA specifies anEIA/TIA specifies an RJRJ--4545 connector for UTPconnector for UTP

cablecable RJRJ stand forstand for Registered JackRegistered Jack

4545 refers to the specificrefers to the specific wiring sequencewiring sequence

AA transceivertransceiver converts one type of connection toconverts one type of connection to

anotheranotherExample: AUI to RJExample: AUI to RJ--45, coax, or fiber optic connector45, coax, or fiber optic connector

Straight-throughCrossover

Switch to router

Switch to PC or server

Hub to PC or server

X to no X

Switch to switch

Switch to hub

Hub to hub

Router to router

PC to PC

Router to PC

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DigitalIntel

Xerox

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This is theConnector

This is theJack

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This is theJack

This is theConnector568A

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This is theJack

This is theConnector

568B

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ProperlyCrimped

Good JacketLength

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Transmit DataTip +ve

Transmit DataRing -ve

Receive DataTip +ve

Receive DataRing -ve568B

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568B 568A

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Use straight-through cables for

Sw

itch

to routerSwitch to PC or serverHub to PC or server

Use crossover cables forSwitch to switchSwitch to hub

Hub to hubRouter to routerPC to PC

Router to PC

Use roll-over cables toConnect a terminal to aconsole port

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1. Two computers typically communicate

with each other by usingrequest/response protocols.

2. The requestor takes on the role of aclient, and the responder takes on the

role of a server.3. In a peer-to-peer network, networked

computers act as equal partners, or peers.4. As peers, each computer can take on the

client function or the server function.5. Recommended maximum numberof peer-

to-peerhostsis 10.

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In a peer-to-peer network,individual users control theirown resources.

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Peer-to-peer networks are relatively easy to install and

operate.No additional equipment is necessary beyond a suitableoperating system installed on each computer.Since users control their own resources, no dedicated

administrators are needed.

As netw

orks grow

, peer-to-peer relationships becomeincreasingly difficult to coordinate.

A peer-to-peer network works well with10 orfewercomputers.Their efficiency decreases rapidly as the number of computerson the network increases.Also, individual users control access to the resources on theircomputers, which means security may be difficult to maintain.The client/server model of networking can be used toovercome the limitations of the peer-to-peer network.

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In a client/server arrangement, network services are located on a dedicated

server. The server is a centralcomputer that is continuously available to respond torequests from clients for file, print, application, and other services.

Most network operating systems adopt the form of a client/server relationship. Typically, desktop computers are the clients and one or more computers with

additional processing power, memory, and specializedsoftware function asservers.

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