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Comparison and ContrastComparison and Contrastbetween the OSI andbetween the OSI and

TCP/IP ModelTCP/IP Model

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IntroductionIntroduction The topics that we will be discussingThe topics that we will be discussing

would be based on the diagram below.would be based on the diagram below.OSI TCP / IP

Application (Layer7)Application

Presentation (Layer6)

Session (Layer 5)

Transport (Layer 4) Transport

Network (Layer 3) Internet

Data Link (Layer 2)Subnet

Physical (Layer 1)

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OutlineOutline Compare the protocol layers thatCompare the protocol layers that

correspond to each other.correspond to each other.

General ComparisonGeneral Comparison

Focus of Reliability ControlFocus of Reliability Control

Roles of Host systemRoles of Host system

DeDe--jure vs. Dejure vs. De--factofacto

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The Upper LayersThe Upper LayersOSI TCP / IP

Application (Layer7)

Application

Presentation (Layer6)

Session (Layer 5)

SessionSession

PresentationPresentation

ApplicationApplication

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The Session LayerThe Session LayerThe Session layerThe Session layer permits two parties topermits two parties tohold ongoing communications called ahold ongoing communications called asession across a networksession across a network..

Not found in TCP/IP modelNot found in TCP/IP model

In TCP/IP,itsIn TCP/IP,its characteristicscharacteristics areare

provided by the TCP protocol.provided by the TCP protocol.

(Transport Layer)(Transport Layer)

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The Presentation LayerThe Presentation LayerThe Presentation Layer handles data formatThe Presentation Layer handles data formatinformation for networked communications.information for networked communications.

This is done by converting data into a genericThis is done by converting data into a genericformat that could be understood by bothformat that could be understood by bothsides.sides.

Not found in TCP/IP modelNot found in TCP/IP model

In TCP/IP, this function is provided by theIn TCP/IP, this function is provided by theApplication Layer.Application Layer.

e.g.e.g. External Data Representation Standard (XDR)External Data Representation Standard (XDR)Multipurpose Internet Mail ExtensionsMultipurpose Internet Mail Extensions (MIME)(MIME)

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The Application LayerThe Application LayerThe Application Layer is the top layer of theThe Application Layer is the top layer of thereference model. It provides a set of interfaces forreference model. It provides a set of interfaces forapplications to obtain access to networked servicesapplications to obtain access to networked services

as well as access to the kinds of network servicesas well as access to the kinds of network servicesthat support applications directly.that support applications directly.

OSIOSI -- FTAM,VT,MHS,DS,CMIPFTAM,VT,MHS,DS,CMIP

TCP/IPTCP/IP -- FTP,SMTP,TELNET,DNS,SNMPFTP,SMTP,TELNET,DNS,SNMP

Although the notion of an application process isAlthough the notion of an application process iscommon to both, their approaches to constructingcommon to both, their approaches to constructingapplication entities is different.application entities is different.

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Approaches use in constructingApproaches use in constructing

application entitiesapplication entities The diagram below provides an overall view on theThe diagram below provides an overall view on the

methods use by both themethods use by both the OSIOSI andand TCP/IPTCP/IP model.model.

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ISO ApproachISO Approach Sometime calledSometime called Horizontal ApproachHorizontal Approach

OSI asserts that distributed applicationsOSI asserts that distributed applications

operate over a strict hierarchy of layers andoperate over a strict hierarchy of layers andare constructed from a common tool kit ofare constructed from a common tool kit ofstandardized application service elements.standardized application service elements.

In OSI, each distributed application serviceIn OSI, each distributed application service

selects functions from a large commonselects functions from a large commontoolbox of application service elementtoolbox of application service element(ASEs) and complements these with(ASEs) and complements these withapplication service elements that performapplication service elements that performfunctions specific to given endfunctions specific to given end--user service .user service .

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TCP/IP ApproachTCP/IP Approach Sometime calledSometime calledVertical ApproachVertical Approach

In TCP/IP, each application entity isIn TCP/IP, each application entity is

composed of whatever set of function itcomposed of whatever set of function itneeds beyond end to end transport toneeds beyond end to end transport tosupport a distributed communications service.support a distributed communications service.

Most of these application processes builds onMost of these application processes builds onwhat it needs and assumes only that anwhat it needs and assumes only that anunderlying transport mechanism (datagramunderlying transport mechanism (datagramor connection) will be provided.or connection) will be provided.

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Transport LayerTransport Layer

The functionality of the transport layerThe functionality of the transport layeris to provide transparent transfer ofis to provide transparent transfer ofdata from a source end open system todata from a source end open system toa destination end open system (ISO /a destination end open system (ISO /IEC 7498: 1984).IEC 7498: 1984).

OSI TCP / IP

Transport (Layer 4) Transport (TCP/UDP)

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Transport LayerTransport Layer Transport is responsible for creatingTransport is responsible for creating

and maintaining the basic endand maintaining the basic end--toto--endend

connection between communicatingconnection between communicatingopen systems, ensuring that the bitsopen systems, ensuring that the bitsdelivered to the receiver are the samedelivered to the receiver are the same

as the bits transmitted by the sender; inas the bits transmitted by the sender; inthe same order and withoutthe same order and withoutmodification, loss or duplicationmodification, loss or duplication

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OSI Transport LayerOSI Transport Layer It takes the information to be sent andIt takes the information to be sent and

breaks it into individual packets that are sentbreaks it into individual packets that are sent

and reassembled into a complete message byand reassembled into a complete message bythe Transport Layer at the receiving nodethe Transport Layer at the receiving node

Also provide a signaling service for theAlso provide a signaling service for theremote node so that the sending node isremote node so that the sending node is

notified when its data is received successfullynotified when its data is received successfullyby the receiving nodeby the receiving node

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OSI Transport LayerOSI Transport Layer Transport Layer protocols include theTransport Layer protocols include the

capability to acknowledge the receipt ofcapability to acknowledge the receipt of

a packet; if no acknowledgement isa packet; if no acknowledgement isreceived, the Transport Layer protocolreceived, the Transport Layer protocolcan retransmit the packet or timecan retransmit the packet or time--outout

the connection and signal an errorthe connection and signal an error

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OSI Transport LayerOSI Transport Layer Transport protocols can also mark packetsTransport protocols can also mark packets

with sequencing information so that thewith sequencing information so that the

destination system can properly order thedestination system can properly order thepackets if theyre received outpackets if theyre received out--ofof--sequencesequence

In addition, Transport protocols provideIn addition, Transport protocols providefacilities for insuring the integrity of packetsfacilities for insuring the integrity of packets

and requesting retransmission should theand requesting retransmission should thepacket become garbled when routed.packet become garbled when routed.

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OSI Transport LayerOSI Transport Layer Transport protocols provide theTransport protocols provide the

capability for multiple applicationcapability for multiple application

processes to access the network byprocesses to access the network byusing individual local addresses tousing individual local addresses todetermine the destination process fordetermine the destination process for

each data streameach data stream

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TCP/IP Transport LayerTCP/IP Transport Layer Defines two standard transportDefines two standard transport

protocols: TCP and UDPprotocols: TCP and UDP

TCP implements a reliable dataTCP implements a reliable data--streamstreamprotocolprotocol connection orientedconnection oriented

UDP implements an unreliable dataUDP implements an unreliable data--streamstream connectionlessconnectionless

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TCP/IP Transport LayerTCP/IP Transport Layer TCP provides reliable data transmissionTCP provides reliable data transmission

UDP is useful in many applicationsUDP is useful in many applications

eg. Where data needs to be broadcastedeg. Where data needs to be broadcastedor multicastedor multicasted

Primary difference is that UDP does notPrimary difference is that UDP does not

necessarily provide reliable datanecessarily provide reliable datatransmissiontransmission

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TCP/IP Transport LayerTCP/IP Transport Layer Many programs will use a separate TCPMany programs will use a separate TCP

connection as well as a UDP connectionconnection as well as a UDP connection

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TCP/IP Transport LayerTCP/IP Transport Layer TCP is responsible for data recoveryTCP is responsible for data recovery

by providing a sequence number with eachby providing a sequence number with each

packet that it sendspacket that it sends

TCP requires ACK (ackowledgement) toTCP requires ACK (ackowledgement) toensure correct data is receivedensure correct data is received

Packet can be retransmitted if errorPacket can be retransmitted if errordetecteddetected

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TCP/IP Transport LayerTCP/IP Transport Layer Use of ACKUse of ACK

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TCP/IP Transport LayerTCP/IP Transport Layer Flow control withFlow control with WindowWindow

via specifying an acceptable range ofvia specifying an acceptable range of

sequence numberssequence numbers

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TCP/IP Transport LayerTCP/IP Transport Layer TCP and UDP introduce the concept ofTCP and UDP introduce the concept of

portsports

Common ports and the services that runCommon ports and the services that runon them:on them:

FTPFTP 21 and 2021 and 20

telnettelnet 2323

SMTPSMTP 2525

httphttp 8080

POP3POP3 110110

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TCP/IP Transport LayerTCP/IP Transport Layer By specifying ports and including portBy specifying ports and including port

numbers with TCP/UDP data,numbers with TCP/UDP data, multiplexingmultiplexing isis

achievedachieved Multiplexing allows multiple networkMultiplexing allows multiple network

connections to take place simultaneouslyconnections to take place simultaneously

The port numbers, along with the source andThe port numbers, along with the source anddestination addresses for the data, determinedestination addresses for the data, determineaa socketsocket

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Comparing Transport for both ModelsComparing Transport for both Models The features of UDP and TCP defined atThe features of UDP and TCP defined at

TCP/IP Transport Layer correspond to manyTCP/IP Transport Layer correspond to many

of the requirements of the OSI Transportof the requirements of the OSI TransportLayer. There is a bit of bleed over forLayer. There is a bit of bleed over forrequirements in the session layer of OSI sincerequirements in the session layer of OSI sincesequence numbers, and port values can helpsequence numbers, and port values can helpto allow the Operating System to keep trackto allow the Operating System to keep track

of sessions, but most of the TCP and UDPof sessions, but most of the TCP and UDPfunctions and specifications map to the OSIfunctions and specifications map to the OSITransport Layer.Transport Layer.

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Comparing Transport for both ModelsComparing Transport for both Models The TCP/IP and OSI architecture models bothThe TCP/IP and OSI architecture models both

employ all connection and connectionlessemploy all connection and connectionless

models at transport layer. However, themodels at transport layer. However, theinternet architecture refers to the two modelsinternet architecture refers to the two modelsin TCP/IP as simply connections andin TCP/IP as simply connections anddatagrams. But the OSI reference model,datagrams. But the OSI reference model,with its penchant for precise terminology,with its penchant for precise terminology,

uses the terms connectionuses the terms connection--mode andmode andconnectionconnection--oriented for the connection modeloriented for the connection modeland the term connectionlessand the term connectionless--mode for themode for theconnectionless model.connectionless model.

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Network vs. InternetNetwork vs. Internet

Like all the other OSI Layers, the networkLike all the other OSI Layers, the networklayer provides both connectionless andlayer provides both connectionless and

connectionconnection--oriented services. As for theoriented services. As for theTCP/IP architecture, the internet layer isTCP/IP architecture, the internet layer isexclusively connectionless.exclusively connectionless.

OSI TCP / IP

Network (Layer 3) Internet

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Network vs. InternetNetwork vs. Internet X.25 Packet Level ProtocolX.25 Packet Level Protocol OSIsOSIs

ConnectionConnection--oriented Network Protocoloriented Network Protocol

The CCITT standard for X.25 defines the DTE/DCEThe CCITT standard for X.25 defines the DTE/DCEinterface standard to provide access to a packetinterface standard to provide access to a packet--switched network. It is the network level interface,switched network. It is the network level interface,which specifies a virtual circuit (VC) service. A sourcewhich specifies a virtual circuit (VC) service. A sourcehost must establish a connection (a VC) with thehost must establish a connection (a VC) with thedestination host before data transfer can take place.destination host before data transfer can take place.The network attempts to deliver packets flowing overThe network attempts to deliver packets flowing overa VC in sequence.a VC in sequence.

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Network vs. InternetNetwork vs. Internet Connectionless Network ServiceConnectionless Network Service

Both OSI and TCP/IP support a connectionlessBoth OSI and TCP/IP support a connectionlessnetwork service: OSI as an alternative to networknetwork service: OSI as an alternative to networkconnections and TCP/IP as the only way in use.connections and TCP/IP as the only way in use.

Internetworking ProtocolsInternetworking Protocols OSIs CLNP (ISO/IEC 8473: 1993) is functionallyOSIs CLNP (ISO/IEC 8473: 1993) is functionally

identical to the Internets IP (RPC 791). Both CLNPidentical to the Internets IP (RPC 791). Both CLNP

and IP are bestand IP are best--efforteffort--delivery network protocols.delivery network protocols.Bit niggling aside, they are virtually identical. TheBit niggling aside, they are virtually identical. Themajor difference between the two is that CLNPmajor difference between the two is that CLNPaccommodates variableaccommodates variable--length addresses,length addresses,whereas IP supports fixed, 32whereas IP supports fixed, 32--bit address.bit address.

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Network vs. InternetNetwork vs. Internet Internet (IP) AddressesInternet (IP) Addresses

The lnternet network address is more commonlyThe lnternet network address is more commonlycalled the IP address. It consists of 32 bits,called the IP address. It consists of 32 bits,some of which are allocated to a highsome of which are allocated to a high--orderordernetworknetwork--numbernumber part and the remainder of whichpart and the remainder of whichare allocated to a loware allocated to a low--order hostorder host--numbernumber part.part.The distribution of bitsThe distribution of bits -- how many form thehow many form thenetwork number, and how many are therefore leftnetwork number, and how many are therefore leftfor the host numberfor the host number -- can be done in one of threecan be done in one of threedifferent ways, giving three differentdifferent ways, giving three different classesclasses of IPof IPaddressaddress

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Network vs. InternetNetwork vs. Internet OSI Network Layer AddressingOSI Network Layer Addressing

ISO/IEC and CCITT jointly administer the globalISO/IEC and CCITT jointly administer the globalnetwork addressing domain. The initialnetwork addressing domain. The initialhierarchical decomposition of the NSAP address ishierarchical decomposition of the NSAP address isdefined by (ISO/IEC 8348). The standard specifiesdefined by (ISO/IEC 8348). The standard specifiesthe syntax and the allowable values for the highthe syntax and the allowable values for the high--order part of the addressorder part of the address -- the Initial Domain Partthe Initial Domain Part(IDP), which consists of the Authority and Format(IDP), which consists of the Authority and FormatIdentifier (AFI) and the Initial Domain IdentifierIdentifier (AFI) and the Initial Domain Identifier(IDI)(IDI) -- but specifically eschews constraints on orbut specifically eschews constraints on orrecommendations concerning the syntax orrecommendations concerning the syntax orsemantics of the domain specific part (DSP).semantics of the domain specific part (DSP).

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Network vs. InternetNetwork vs. Internet OSI Routing ArchitectureOSI Routing Architecture

End systems (ESs) and intermediate systems (ISs)End systems (ESs) and intermediate systems (ISs)use routing protocols to distribute (advertise)use routing protocols to distribute (advertise)some or all of the information stored in theirsome or all of the information stored in theirlocally maintained routing information base. ESslocally maintained routing information base. ESsand ISs send and receive these routing updatesand ISs send and receive these routing updatesand use the information that they contain (andand use the information that they contain (andinformation that may be available from the localinformation that may be available from the localenvironment, such as information enteredenvironment, such as information enteredmanually by an operator) to modify their routingmanually by an operator) to modify their routinginformation base.information base.

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Network vs. InternetNetwork vs. Internet TCP/IP Routing ArchitectureTCP/IP Routing Architecture

The TCP/IP routing architecture looks very muchThe TCP/IP routing architecture looks very muchlike the OSI routing architecture. Hosts use alike the OSI routing architecture. Hosts use adiscovery protocol to obtain the identification ofdiscovery protocol to obtain the identification ofgateways and other hosts attached to the samegateways and other hosts attached to the samenetwork (subnetwork). Gateways withinnetwork (subnetwork). Gateways withinautonomous systems (routing domains) operateautonomous systems (routing domains) operatean interior gateway protocol (intradomain ISan interior gateway protocol (intradomain IS--ISISrouting protocol), and between autonomousrouting protocol), and between autonomoussystems, they operate exterior or border gatewaysystems, they operate exterior or border gatewayprotocols (interdomain routing protocols). Theprotocols (interdomain routing protocols). Thedetails are different but the principles are thedetails are different but the principles are thesame.same.

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Data link / Physical vs. SubnetData link / Physical vs. Subnet

Data link layerData link layer The function of theData Link Layeris provides for the control of

the physical layer, and detects and possibly corrects errors whichmay occur (IOS/IEC 7498:1984). In another words, the DataLink Layer transforms a stream of raw bits (0s and 1s) from thephysical into a data frame and provides an error-free transfer fromone node to another, allowing the layers above it to assumevirtually error-free transmission

OSI TCP / IP

Data Link (Layer 2)

Subnet

Physical (Layer 1)

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Data link / Physical vs. SubnetData link / Physical vs. Subnet Physical layerPhysical layer

The function of the Physical Layeris to provide

mechanical, electrical, functional, and proceduralmeans to activate a physical connection for bit

transmission (ISO/IEC 7498:1984). Basically, this

means that the typical role of the physical layer is to

transform bits in a computer system into

electromagnetic (or equivalent) signals for a particulartransmission medium (wire, fiber, ether, etc.)

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Data link / Physical vs. SubnetData link / Physical vs. Subnet Comparing to TCP/IPComparing to TCP/IP

These 2 layers of the OSI correspond directly to the subnet layer ofthe TCP/IP model.

Majority of the time, the lower layers below the Interface or

Network layer of the TCP/IP model are seldom or rarely discussed.

The TCP/IP model does nothing but to high light the fact the hosthas to connect to the network using some protocol so it can send IP

packets over it. Because the protocol used is not defines, it will

vary from host to host and network to network

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Data link / Physical vs. SubnetData link / Physical vs. Subnet Comparing to TCP/IPComparing to TCP/IP

After much deliberation by organizations, it was

decided that the Network Interface Layer in the TCP/IPmodel corresponds to a combination of the OSI DataLink Layer and network specific functions of the OSInetwork layer (eg IEEE 203.3).

Since these two layers deal with functions that are soinherently specific to each individual networkingtechnology, the layering principle of grouping themtogether related functions is largely irrelevant.

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General ComparisonGeneral Comparison

Focus of Reliability ControlFocus of Reliability Control

Roles of Host SystemRoles of Host System

DeDe--jure vs. Dejure vs. De--factofacto

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Roles of Host SystemRoles of Host System Hosts on OSI implementations do notHosts on OSI implementations do not

handle network operations (simplehandle network operations (simple

terminal), but TCP/IP hosts participateterminal), but TCP/IP hosts participatein most network protocols. TCP/IP hostsin most network protocols. TCP/IP hostscarry out such functions as endcarry out such functions as end--toto--endendverification, routing, and networkverification, routing, and network

control. The TCP/IP internet can becontrol. The TCP/IP internet can beviewed as a data stream deliveryviewed as a data stream deliverysystem involving intelligent hosts.system involving intelligent hosts.

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DeDe--jure vs. Dejure vs. De--facto (OSI)facto (OSI) OSIOSI

StandardStandard legislatedlegislated byby officialofficial recognizedrecognized bodybody.. (ISO)(ISO)

TheThe OSIOSI referencereference modelmodel waswas deviseddevised beforebefore thethe protocolsprotocols werewere

inventedinvented.. ThisThis orderingordering meansmeans thatthat thethe modelmodel waswas not not biasedbiasedtowardtoward oneone particularparticular setset of of protocols,protocols, whichwhich mademade it it quitequitegeneralgeneral.. TheThe downdown sideside ofof thisthis orderingordering isis thatthat thethe designersdesigners diddidnotnot havehave muchmuch experienceexperience withwith thethe subjectsubject andand diddid notnot havehave aagoodgood ideaidea ofof whichwhich functionalityfunctionality toto putput inin whichwhich layerlayer..

BeingBeing general,thegeneral,the protocolsprotocols inin thethe OSIOSI modelmodel areare betterbetter hiddenhidden

thanthan inin thethe TCP/IPTCP/IP modelmodel andand cancan bebe replacedreplaced relativelyrelatively easilyeasily asasthethe technologytechnology changeschanges..

NotNot soso widespreadwidespread asas comparedcompared withwith TCP/IPTCP/IP.. (complex(complex ,, costly)costly)

MoreMore commonlycommonly usedused asas teachingteaching aidsaids..

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DeDe--jure vs. Dejure vs. De--facto (TCP/IP)facto (TCP/IP) TCP/IPTCP/IP

Standards adopted due to widespread use. (Internet)Standards adopted due to widespread use. (Internet)

The protocols came first, and the model was really just aThe protocols came first, and the model was really just a

description of the existing protocols. There was no problemdescription of the existing protocols. There was no problemwith the protocols fitting the model, but it is hardly possiblewith the protocols fitting the model, but it is hardly possibleto be use to describe other modelsto be use to describe other models..

Get the job done" orientation.Get the job done" orientation.

Over the years it has handled most challenges by growing toOver the years it has handled most challenges by growing tomeet the needs.meet the needs.

More popular standard for internetworking for severalMore popular standard for internetworking for severalreasons :reasons :

relatively simple and robust compared to alternatives such as OSIrelatively simple and robust compared to alternatives such as OSI

available on virtually every hardware and operating system platformavailable on virtually every hardware and operating system platform(often free)(often free)

the protocol suite on which the Internet depends.the protocol suite on which the Internet depends.

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The EndThe End Project team membersProject team members

ANDREW TAN TENG HONGANDREW TAN TENG HONG

MAH CHEE MENGMAH CHEE MENG

CHEE YEW WAICHEE YEW WAI

TAN YOKE CHUANTAN YOKE CHUAN

CHEONG KIM MINGCHEONG KIM MING