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Comparison of OSI Reference Model and TCP/IP

Reference Model

Following are some major differences between OSI Reference Model and TCP/IP Reference Model, with

diagrammatic comparison below

OSI(Open System Interconnection) TCP/IP(Transmission Control Protocol /

Internet Protocol)

! OSI pro"ides la#er f$nctioning and also defines

f$nctions of all the la#ers

! TCP/IP model is more based on protocols and

protocols are not fle%ible with other la#ers

& In OSI model the transport la#er g$arantees the

deli"er# of pac'ets

& In TCP/IP model the transport la#er does not

g$arantees deli"er# of pac'ets

( Follows hori)ontal approach ( Follows "ertical approach

* OSI model has a separate presentation la#er * TCP/IP does not ha"e a separate presentation

la#er

+ OSI is a general model + TCP/IP model cannot be $sed in an# other

application

-etwor' la#er of OSI model pro"ide both

connection oriented and connectionless ser"ice

The -etwor' la#er in TCP/IP model pro"ides

connectionless ser"ice

. OSI model has a problem of fitting the protocols in

the model

. TCP/IP model does not fit an# protocol

Protocols are hidden in OSI model and are easil#

replaced as the technolog# changes

In TCP/IP replacing protocol is not eas#

0 OSI model defines ser"ices, interfaces and

protocols "er# clearl# and ma'es clear distinction

between them

0 In TCP/IP it is not clearl# separated its

ser"ices, interfaces and protocols

!1 It has . la#ers !1 It has * la#ers

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agrammatic Comparison between OSI Reference Model and TCP/IPeference Model

ATA LINK Layer - OSI Model

a lin' la#er is most reliable node to node deli"er# of data It forms frames from the pac'ets that are recei"ed from

wor' la#er and gi"es it to ph#sical la#er It also s#nchroni)es the information which is to be transmitted o"er the

a 3rror controlling is easil# done The encoded data are then passed to ph#sical

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or detection bits are $sed b# the data lin' la#er It also corrects the errors O$tgoing messages are assembled into

mes Then the s#stem waits for the ac'nowledgements to be recei"ed after the transmission It is reliable to send

ssage

UNCTIONS OF DT !IN" !#$R%

Framing:Frames are the streams of bits recei"ed from the networ' la#er into manageable data $nits This

di"ision of stream of bits is done b# 2ata 4in' 4a#er

Physical Addressing: The 2ata 4in' la#er adds a header to the frame in order to define ph#sical address of

the sender or recei"er of the frame, if the frames are to be distrib$ted to different s#stems on the networ'

Flow Control:5 flow control mechanism to a"oid a fast transmitter from r$nning a slow recei"er b# b$ffering

the e%tra bit is pro"ided b# flow control This pre"ents traffic jam at the recei"er side

Error Control: 3rror control is achie"ed b# adding a trailer at the end of the frame 2$plication of frames are

also pre"ented b# $sing this mechanism 2ata 4in' 4a#ers adds mechanism to pre"ent d$plication of frames

Access Control: Protocols of this la#er determine which of the de"ices has control o"er the lin' at an# gi"en

time, when two or more de"ices are connected to the same lin'

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oadly HDLC features are as follows: Reliable protocol selective repeat or go-back-N ull-duple!

""u#icatio# receive a#d tra#s"it at t$e sa"e ti"e Bit-orie#ted protocol use bits to stuff flags occurri#g

data low co#trol ad%ust wi#dow si&e based o# receiver capability 'ses p$ysical layer clocki#g a#d

c$ro#i&atio# to se#d a#d receive fra"es

Question T7.2 - Instead of LLC, ould !DLC "e used as a data lin# ontrol $rotool for a LAN% If

not, &'at is la#in(% !DLC 'as only one address )eld *usually use to address t'e seondarystation in a $ri+ary and seondary on)(uration. In a LAN, any station +ay trans+it to any

ot'er station. T'e reeiin( station needs to see its o&n address in order to #no& t'at t'e data

s intended for itself. It also needs to see t'e sendin( address in order to re$ly

Dierenes "et&een TDMA, CDMA, and /DMA 0it' a #no&led(e+ent and a$$reiation to My

Lord on 1a'oo Ans&ers TDMA Ti+e diision +ulti$le aess *TDMA is a 'annel aess +et'od

for s'ared +ediu+ *usually radio net&or#s. It allo&s seeral users to s'are t'e sa+e

freueny 'annel "y diidin( t'e si(nal into dierent ti+eslots. T'e users trans+it in ra$id

suession, one after t'e ot'er, ea' usin( 'is o&n ti+eslot. T'is allo&s +ulti$le stations to

s'are t'e sa+e trans+ission +ediu+ *e.(. radio freueny 'annel &'ile usin( only t'e $art

of its "and&idt' t'ey reuire. TDMA is used in t'e di(ital 23 ellular syste+s su' as 3lo"al

Syste+ for Mo"ile Co++uniations *3SM, IS-456, ersonal Di(ital Cellular *DC and iD8N, and

n t'e Di(ital 8n'aned Cordless Teleo++uniations *D8CT standard for $orta"le $'ones. It is

also used e9tensiely in satellite syste+s, and o+"at-net radio syste+s. TDMA is a ty$e of

Ti+e-diision +ulti$le9in(, &it' t'e s$eial $oint t'at instead of 'ain( one trans+itter

onneted to one reeier, t'ere are +ulti$le trans+itters. In t'e ase of t'e u$lin# fro+ a

+o"ile $'one to a "ase station t'is "eo+es $artiularly di:ult "eause t'e +o"ile $'one

an +oe around and ary t'e ti+in( adane reuired to +a#e its trans+ission +at' t'e (a$

n trans+ission fro+ its $eers CDMA Code diision +ulti$le aess *CDMA is a for+ of+ulti$le9in( and a +et'od of +ulti$le aess t'at diides u$ a radio 'annel not "y ti+e *as in

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ti+e diision +ulti$le aess, nor "y freueny *as in freueny-diision +ulti$le aess, "ut

nstead "y usin( dierent $seudorando+ ode seuenes for ea' user. CDMA is a for+ of

;s$read-s$etru+; si(nalin(, sine t'e +odulated oded si(nal 'as a +u' 'i('er "and&idt'

t'an t'e data "ein( o++uniated. CDMA also refers to di(ital ellular tele$'ony syste+s t'at

+a#e use of t'is +ulti$le aess s'e+e, su' as t'ose $ioneered "y Qfreueny diision? indiates 'o& t'e s'arin( is ao+$lis'ed@ "y alloatin( indiidual

freuenies for ea' o++uniations si(nal &it'in t'e "and. In an /DMA s'e+e, t'e (ien

=adio /reueny *=/ "and&idt' is diided into adBaent freueny se(+ents. 8a' se(+ent is$roided &it' "and&idt' to ena"le an assoiated o++uniations si(nal to $ass t'rou(' a

trans+ission eniron+ent &it' an ae$ta"le leel of interferene fro+ o++uniations

si(nals in adBaent freueny se(+ents

y$es of Net&or# To$olo(y

wor' Topolog# is the schematic description of a networ' arrangement, connecting "ario$s nodes6sender and

ei"er7 thro$gh lines of connection

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If networ' traffic is hea"# or nodes are more the performance of the networ' decreasesCable has a limited lengthIt is slower than the ring topolog#

N3 To$olo(y

called ring topolog# beca$se it forms a ring as each comp$ter is connected to another comp$ter, with the last connected to the first 3%actl# two neighbo$rs for each de"ice

at&res of Ring Topolog(5 n$mber of repeaters are $sed and the transmission is $nidirectional2ate is transferred in a se9$ential manner that is bit b# bit

d)antages of Ring Topolog(Transmitting networ' is not affected b# high traffic or b# adding more nodes, as onl# the nodes ha"ing to'ens

can transmit dataCheap to install and e%pand

sad)antages of Ring Topolog(Tro$bleshooting is diffic$lt in ring topolog#5dding or deleting the comp$ters dist$rbs the networ' acti"it#Fail$re of one comp$ter dist$rbs the whole networ'

TA= To$olo(y

his t#pe of topolog# all the comp$ters are connected to a single h$b thro$gh a cable This h$b is the central node all others nodes are connected to the central node

at&res of Star Topolog(3"er# node has its own dedicated connection to the h$b5cts as a repeater for data flowCan be $sed with twisted pair, Optical Fibre or coa%ial cable

d)antages of Star Topolog(Fast performance with few nodes and low networ' traffic;$b can be $pgraded easil#3as# to tro$bleshoot3as# to set$p and modif#

Onl# that node is affected which has failed rest of the nodes can wor' smoothl#sad)antages of Star Topolog(Cost of installation is high3%pensi"e to $seIf the h$b is affected then the whole networ' is stopped beca$se all the nodes depend on the h$bPerformance is based on the h$b that is it depends on its capacit#

8S! To$olo(y

a point

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(pes of Mes* Topolog(Partial esh Topology : In this topolog# some of the s#stems are connected in the same fashion as mesh

topolog# b$t some de"ices are onl# connected to two or three de"icesF!ll esh Topology : 3ach and e"er# nodes or de"ices are connected to each other

at&res of Mes* Topolog(F$ll# connected

Rob$st-ot fle%ible

d)antages of Mes* Topolog(3ach connection can carr# its own data loadIt is rob$stFa$lt is diagnosed easil#Pro"ides sec$rit# and pri"ac#

sad)antages of Mes* Topolog(Installation and config$ration is diffic$ltCabling cost is more8$l' wiring is re9$ired

=88 To$olo(y

as a root node and all other nodes are connected to it forming a hierarch# It is also called hierarchical topolog# It$ld at least ha"e three le"els to the hierarch#

at&res of Tree Topolog(Ideal if wor'stations are located in gro$ps

:sed in =ide 5rea -etwor'd)antages of Tree Topolog(3%tension of b$s and star topologies3%pansion of nodes is possible and eas#3asil# managed and maintained3rror detection is easil# done

sad)antages of Tree Topolog(;ea"il# cabledCostl#If more nodes are added maintenance is diffic$ltCentral h$b fails, networ' fails

1=ID To$olo(y

two different t#pes of topologies which is a mi%t$re of two or more topologies For e%ample if in an office in oneartment ring topolog# is $sed and in another star topolog# is $sed, connecting these topologies will res$lt in

brid Topolog# 6ring topolog# and star topolog#7

at&res of +(brid Topolog(It is a combination of two or topologies

Inherits the ad"antages and disad"antages of the topologies incl$ded

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d)antages of +(brid Topolog(Reliable as 3rror detecting and tro$ble shooting is eas#3ffecti"eScalable as si)e can be increased easil#Fle%ible

sad)antages of +(brid Topolog(Comple% in designCostl#