osi and tcp/ip comparison

8/14/2019 osi and tcp/ip comparison

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IntroductionIntroduction

The topics that we will beThe topics that we will be

discussing would be based on thediscussing would be based on the

diagram below.diagram below.

OSI TCP / IP

Application (Layer7)

ApplicationPresentation (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

De-jure vs. De-factoDe-jure vs. De-facto


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The Upper LayersThe Upper Layers

OSI TCP / IP

Application (Layer7)

ApplicationPresentation (Layer6)

Session (Layer 5)

SessionSession

PresentationPresentation

ApplicationApplication


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The Session LayerThe Session Layer

The Session layerThe Session layer permits twopermits two

parties to hold ongoingparties to hold ongoing

communications called a sessioncommunications called a sessionacross a networkacross a network..

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

In TCP/IP,itsIn TCP/IP,its characteristicscharacteristics areareprovided by the TCP protocol.provided by the TCP protocol.

(Transport Layer)(Transport Layer)


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The Presentation LayerThe Presentation Layer

The Presentation Layer handles dataThe Presentation Layer handles dataformat information for networkedformat information for networkedcommunications. This is done bycommunications. This is done byconverting data into a generic formatconverting data into a generic formatthat could be understood by both sides.that could be understood by both sides.

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

In TCP/IP, this function is provided byIn TCP/IP, this function is provided bythe Application Layer.the 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 Layer

The Application Layer is the top layer of theThe Application Layer is the top layer of thereference model. It provides a set of interfacesreference model. It provides a set of interfacesfor applications to obtain access to networkedfor applications to obtain access to networked

services as well as access to the kinds ofservices as well as access to the kinds ofnetwork services that support applicationsnetwork services that support applicationsdirectly.directly.

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

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

Although the notion of an application processAlthough the notion of an application processis common to both, their approaches tois common to both, their approaches to

constructing application entities is different.constructing 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 onThe diagram below provides an overall view on

the methods use by both thethe methods use by both the OSIOSI andandTCP/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 layersoperate over a strict hierarchy of layersand are constructed from a commonand are constructed from a commontool kit of standardized applicationtool kit of standardized applicationservice elements.service elements.

In OSI, each distributed applicationIn OSI, each distributed applicationservice selects functions from a largeservice selects functions from a largecommon toolbox of applicationcommon toolbox of applicationservice element (ASEs) andservice element (ASEs) and

complements these with applicationcomplements these with applicationservice elements that perform functionsservice elements that perform functions


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TCP/IP ApproachTCP/IP Approach

Sometime calledSometime called Vertical 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 to

support a distributed communicationssupport a distributed communications

service.service.

Most of these application processesMost of these application processes

builds on what it needs and assumesbuilds on what it needs and assumes

only that an underlying transportonly that an underlying transport

mechanism (datagram or connection)mechanism (datagram or connection)will be rovided.will be rovided.


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Transport LayerTransport Layer

The functionality of the transportThe functionality of the transport

layer is to provide transparentlayer is to provide transparent

transfer of data from a source endtransfer of data from a source end

open system to a destination endopen system to a destination end

open system (ISO / IEC 7498:open system (ISO / IEC 7498:

1984).1984).

OSI TCP / IP

Transport (Layer 4) Transport (TCP/UDP)


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Transport LayerTransport Layer

Transport is responsible forTransport is responsible for

creating and maintaining the basiccreating and maintaining the basic

end-to-end connection betweenend-to-end connection betweencommunicating open systems,communicating open systems,

ensuring that the bits delivered toensuring that the bits delivered to

the receiver are the same as thethe receiver are the same as thebits transmitted by the sender; inbits transmitted by the sender; in

the same order and withoutthe same order and without

modification, 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 arebreaks it into individual packets that are

sent and reassembled into a completesent and reassembled into a completemessage by the Transport Layer at themessage by the Transport Layer at the

receiving nodereceiving node

Also provide a signaling service for theAlso provide a signaling service for the

remote node so that the sending noderemote node so that the sending nodeis notified when its data is receivedis notified when its data is received

successfully by the receiving nodesuccessfully by the receiving node


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Transport Layer protocols includeTransport Layer protocols include

the capability to acknowledge thethe capability to acknowledge the

receipt of a packet; if noreceipt of a packet; if noacknowledgement is received, theacknowledgement is received, the

Transport Layer protocol canTransport Layer protocol can

retransmit the packet or time-outretransmit the packet or time-outthe connection and signal an errorthe connection and signal an error


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Transport protocols can also markTransport protocols can also mark

packets with sequencing information sopackets with sequencing information so

that the destination system canthat the destination system canproperly order the packets if theyreproperly order the packets if theyre

received out-of-sequencereceived out-of-sequence

In addition, Transport protocols provideIn addition, Transport protocols provide

facilities for insuring the integrity offacilities for insuring the integrity ofpackets and requesting retransmissionpackets and requesting retransmission

should the packet become garbledshould the packet become garbled

when routed.when routed.


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Transport protocols provide theTransport protocols provide the

capability for multiple applicationcapability for multiple application

processes to access the networkprocesses to access the networkby using individual local addressesby using individual local addresses

to determine the destinationto determine the destination

process for each data streamprocess for each data stream


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TCP/IP Transport LayerTCP/IP Transport Layer

Defines two standard transportDefines two standard transportprotocols: TCP and UDPprotocols: TCP and UDP

TCP implements a reliable data-TCP implements a reliable data-stream protocolstream protocol connection orientedconnection oriented

UDP implements an unreliableUDP implements an unreliabledata-streamdata-stream connectionlessconnectionless


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TCP provides reliable dataTCP provides reliable data

transmissiontransmission

UDP is useful in many applicationsUDP is useful in many applications

eg. Where data needs to beeg. Where data needs to be

broadcasted or multicastedbroadcasted or multicasted Primary difference is that UDPPrimary difference is that UDP

does not necessarily providedoes not necessarily provide

reliable data transmissionreliable data transmission


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Many programs will use a separateMany programs will use a separate

TCP connection as well as a UDPTCP connection as well as a UDP

connectionconnection


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TCP is responsible for dataTCP is responsible for data

recoveryrecovery by providing a sequence number withby providing a sequence number with

each packet that it sendseach packet that it sends

TCP requires ACKTCP requires ACK

(ackowledgement) to ensure(ackowledgement) to ensurecorrect data is receivedcorrect data is received

Packet can be retransmitted ifPacket can be retransmitted if

error detectederror detected


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Use of ACKUse of ACK


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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 and UDP introduce theTCP and UDP introduce the

concept ofconcept ofportsports

Common ports and the servicesCommon ports and the servicesthat run on them:that run on them:

FTPFTP 21 and 2021 and 20 telnettelnet 2323 SMTPSMTP 2525 httphttp 8080 POP3POP3 110110


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By specifying ports and including portBy specifying ports and including port

numbers with TCP/UDP data,numbers with TCP/UDP data,

multiplexingmultiplexing is achievedis achieved Multiplexing allows multiple networkMultiplexing allows multiple network

connections to take placeconnections to take place

simultaneouslysimultaneously

The port numbers, along with theThe port numbers, along with thesource and destination addresses forsource and destination addresses for

the data, determine athe data, determine a socketsocket


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Comparing Transport for bothComparing Transport for both

ModelsModels

The features of UDP and TCP defined atThe features of UDP and TCP defined atTCP/IP Transport Layer correspond toTCP/IP Transport Layer correspond tomany of the requirements of the OSImany of the requirements of the OSI

Transport Layer. There is a bit of bleedTransport Layer. There is a bit of bleedover for requirements in the sessionover for requirements in the sessionlayer of OSI since sequence numbers,layer of OSI since sequence numbers,and port values can help to allow theand port values can help to allow the

Operating System to keep track ofOperating System to keep track ofsessions, but most of the TCP and UDPsessions, but most of the TCP and UDPfunctions and specifications map to thefunctions and specifications map to theOSI Transport Layer.OSI Transport Layer.


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Comparing Transport for bothComparing Transport for both

ModelsModels

The TCP/IP and OSI architecture modelsThe TCP/IP and OSI architecture modelsboth employ all connection andboth employ all connection andconnectionless models at transportconnectionless models at transportlayer. However, the internetlayer. However, the internetarchitecture refers to the two models inarchitecture refers to the two models in

TCP/IP as simply connections andTCP/IP as simply connections anddatagrams. But the OSI referencedatagrams. But the OSI reference

model, with its penchant for precisemodel, with its penchant for preciseterminology, uses the terms connection-terminology, uses the terms connection-mode and connection-oriented for themode and connection-oriented for theconnection model and the termconnection model and the term

connectionless-mode for theconnectionless-mode for the


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Network vs. InternetNetwork vs. Internet

Like all the other OSI Layers, theLike all the other OSI Layers, the

network layer provides bothnetwork layer provides both

connectionless and connection-orientedconnectionless and connection-orientedservices. As for the TCP/IP architecture,services. As for the TCP/IP architecture,

the internet layer is exclusivelythe internet layer is exclusively

connectionless.connectionless.

OSI TCP / IP

Network (Layer 3) Internet


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X.25 Packet Level Protocol OSIsX.25 Packet Level Protocol OSIs

Connection-oriented Network ProtocolConnection-oriented Network Protocol

The CCITT standard for X.25 defines theThe CCITT standard for X.25 defines theDTE/DCE interface standard to provide accessDTE/DCE interface standard to provide access

to a packet-switched network. It is the networkto a packet-switched network. It is the network

level interface, which specifies a virtual circuitlevel interface, which specifies a virtual circuit

(VC) service. A source host must establish a(VC) service. A source host must establish a

connection (a VC) with the destination hostconnection (a VC) with the destination hostbefore data transfer can take place. Thebefore data transfer can take place. The

network attempts to deliver packets flowingnetwork attempts to deliver packets flowing

over a VC in sequence.over a VC in sequence.


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Connectionless Network ServiceConnectionless Network Service Both OSI and TCP/IP support aBoth OSI and TCP/IP support a

connectionless network service: OSI as anconnectionless network service: OSI as an

alternative to network connections andalternative to network connections andTCP/IP as the only way in use.TCP/IP as the only way in use.

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

functionally identical to the Internets IPfunctionally identical to the Internets IP(RPC 791). Both CLNP and IP are best-effort-(RPC 791). Both CLNP and IP are best-effort-delivery network protocols. Bit nigglingdelivery network protocols. Bit nigglingaside, they are virtually identical. The majoraside, they are virtually identical. The majordifference between the two is that CLNPdifference between the two is that CLNP

accommodates variable-length addresses,accommodates variable-length addresses,-


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Internet (IP) AddressesInternet (IP) Addresses The lnternet network address is moreThe lnternet network address is more

commonly called the IP address. Itcommonly called the IP address. It

consists of 32 bits, some of which areconsists of 32 bits, some of which areallocated to a high-order network-numberallocated to a high-order network-numberpart and the remainder of which arepart and the remainder of which areallocated to a low-order host-numberallocated to a low-order host-numberpart.part.

The distribution of bits - how many form theThe distribution of bits - how many form the

network number, and how many arenetwork number, and how many aretherefore left for the host number - can betherefore left for the host number - can bedone in one of three different ways, givingdone in one of three different ways, givingthree differentthree different classesclasses of IP addressof IP address


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OSI Network Layer AddressingOSI Network Layer Addressing ISO/IEC and CCITT jointly administer theISO/IEC and CCITT jointly administer the

global network addressing domain. Theglobal network addressing domain. The

initial hierarchical decomposition of theinitial hierarchical decomposition of theNSAP address is defined by (ISO/IEC 8348).NSAP address is defined by (ISO/IEC 8348).

The standard specifies the syntax and theThe standard specifies the syntax and theallowable values for the high-order part ofallowable values for the high-order part ofthe address - the Initial Domain Part (IDP),the address - the Initial Domain Part (IDP),

which consists of the Authority and Formatwhich consists of the Authority and FormatIdentifier (AFI) and the Initial DomainIdentifier (AFI) and the Initial DomainIdentifier (IDI) - but specifically eschewsIdentifier (IDI) - but specifically eschewsconstraints on or recommendationsconstraints on or recommendationsconcerning the syntax or semantics of theconcerning the syntax or semantics of thedomain specific part (DSP).domain specific part (DSP).


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OSI Routing ArchitectureOSI Routing Architecture End systems (ESs) and intermediateEnd systems (ESs) and intermediate

systems (ISs) use routing protocols tosystems (ISs) use routing protocols to

distribute (advertise) some or all of thedistribute (advertise) some or all of theinformation stored in their locallyinformation stored in their locallymaintained routing information base. ESsmaintained routing information base. ESsand ISs send and receive these routingand ISs send and receive these routingupdates and use the information that theyupdates and use the information that they

contain (and information that may becontain (and information that may beavailable from the local environment, suchavailable from the local environment, suchas information entered manually by anas information entered manually by anoperator) to modify their routing informationoperator) to modify their routing informationbase.base.


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TCP/IP Routing ArchitectureTCP/IP Routing Architecture The TCP/IP routing architecture looks veryThe TCP/IP routing architecture looks very

much like the OSI routing architecture.much like the OSI routing architecture.

Hosts use a discovery protocol to obtain theHosts use a discovery protocol to obtain theidentification of gateways and other hostsidentification of gateways and other hostsattached to the same network (subnetwork).attached to the same network (subnetwork).Gateways within autonomous systemsGateways within autonomous systems(routing domains) operate an interior(routing domains) operate an interior

gateway protocol (intradomain IS-IS routinggateway protocol (intradomain IS-IS routingprotocol), and between autonomousprotocol), and between autonomoussystems, they operate exterior or bordersystems, they operate exterior or bordergateway protocols (interdomain routinggateway protocols (interdomain routingprotocols). The details are different but theprotocols). The details are different but theprinciples are the same.principles are the same.


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Data link / Physical vs.Data link / Physical vs.

SubnetSubnet

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 which

may occur (IOS/IEC 7498:1984). In another words, the DataLink Layer transforms a stream of raw bits (0s and 1s) from the

physical 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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SubnetSubnet

Physical layerPhysical layer

The function of thePhysical Layeris to provide

mechanical, electrical, functional, and procedural

means 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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SubnetSubnet

Comparing to TCP/IPComparing to TCP/IP

These 2 layers of the OSI correspond directly to the subnet layerof the 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 thefact the host has 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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SubnetSubnet

Comparing to TCP/IPComparing to TCP/IP After much deliberation by organizations, it was

decided that the Network Interface Layer in the TCP/IP

model 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



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Focus of Reliability ControlFocus of Reliability Control

Implementation of the OSI model places emphasisImplementation of the OSI model places emphasison providing a reliable data transfer service, whileon providing a reliable data transfer service, whilethe TCP/IP model treats reliability as an end-to-endthe TCP/IP model treats reliability as an end-to-end

problem.problem. Each layer of the OSI model detects and handlesEach layer of the OSI model detects and handles

errors, all data transmitted includes checksums.errors, all data transmitted includes checksums.The transport layer of the OSI model checksThe transport layer of the OSI model checks

source-to-destination reliability.source-to-destination reliability. In the TCP/IP model, reliability control isIn the TCP/IP model, reliability control is

concentrated at the transport layer. The transportconcentrated at the transport layer. The transportlayer handles all error detection and recovery. Thelayer handles all error detection and recovery. The

TCP/IP transport layer uses checksums,TCP/IP transport layer uses checksums,

acknowledgments, and timeouts to controlacknowledgments, and timeouts to control- -- -


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Roles of Host SystemRoles of Host System

Hosts on OSI implementations doHosts on OSI implementations donot handle network operationsnot handle network operations

(simple terminal), but TCP/IP hosts(simple terminal), but TCP/IP hostsparticipate in most networkparticipate in most networkprotocols. TCP/IP hosts carry outprotocols. TCP/IP hosts carry outsuch functions as end-to-endsuch functions as end-to-end

verification, routing, and networkverification, routing, and networkcontrol. 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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De-jure vs. De-facto (OSI)De-jure vs. De-facto (OSI)

OSIOSI Standard legislated by official recognized body. (ISO)Standard legislated by official recognized body. (ISO) The OSI reference model was devisedThe OSI reference model was devised beforebefore the protocolsthe protocols

were invented. This ordering means that the model waswere invented. This ordering means that the model wasnot biased toward one particular set of protocols, whichnot biased toward one particular set of protocols, whichmade it quite general. The down side of this ordering ismade it quite general. The down side of this ordering isthat the designers did not have much experience with thethat the designers did not have much experience with thesubject and did not have a good idea of whichsubject and did not have a good idea of whichfunctionality to put in which layer.functionality to put in which layer.

Being general,the protocols in the OSI model are betterBeing general,the protocols in the OSI model are betterhidden than in the TCP/IP model and can be replacedhidden than in the TCP/IP model and can be replacedrelatively easily as the technology changes.relatively easily as the technology changes.

Not so widespread as compared with TCP/IP. (complex ,Not so widespread as compared with TCP/IP. (complex ,costly)costly)

More commonly used as teaching aids.More commonly used as teaching aids.

j f


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(TCP/IP)(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 reallyThe protocols came first, and the model was really

just a description of the existing protocols. There wasjust a description of the existing protocols. There wasno problem with the protocols fitting the model, butno problem with the protocols fitting the model, butit is hardly possible to be use to describe otherit is hardly possible to be use to describe othermodelsmodels..

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

Over the years it has handled most challenges byOver the years it has handled most challenges by

growing to meet the needs.growing to meet the needs. More popular standard for internetworking forMore popular standard for internetworking for

several reasons :several reasons : relatively simple and robust compared to alternatives such asrelatively simple and robust compared to alternatives such as

OSIOSI available on virtually every hardware and operating systemavailable on virtually every hardware and operating system

platform (often free)platform (often free)


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THANK YOUTHANK YOU

osi and tcp/ip comparison

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