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7/29/2019 Computer Network Ch-4
1/35
OSIReferencemodel
Interlayercommunication
Dataencapsulation
Horizontalcommunication,verticalcommunication
physicallayer;datalinklayer;networklayer;transport
layer; sessionlayer;presentationlayer; applicationlayer.
TCP/IP
Reference
model
Link;
Internet;
Transport;
Application
layer.
ComparisonoftheOSIandTCP/IPreferencemodels
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2/35
OSIReferencemodel
Interlayercommunication
Dataencapsulation
Horizontalcommunication,verticalcommunication
physicallayer;datalinklayer;networklayer;transport
layer; sessionlayer;presentationlayer; applicationlayer.
TCP/IP
Reference
model
Link;
Internet;
Transport;
Application
layer.
ComparisonoftheOSIandTCP/IPreferencemodels
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3/35
OSIReferenceModel
The
OSI
Model
is
a
model
for
understanding
and
designing
a
network
architecture
that
isflexible,robust&interoperable.
he OSI model is a layered framework for the design of network systems that allows
ommunicationbetweenalltypesofcomputersystems.
Application
Presentation
Session
Transport
Network
DataLink
Physical
7
6
5
4
3
2
1
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OSIReferencemodelOSIReferencemodel
Interlayercommunication
Dataencapsulation
Horizontalcommunication,
vertical
communication
physicallayer;datalinklayer;networklayer;transport
layer; sessionlayer;presentationlayer; applicationlayer.
TCP/IPReference
model
Link;
Internet;
Transport;
Application
layer.
ComparisonoftheOSIandTCP/IPreferencemodels
Takeaexample
of
Army
communication
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kk
kk
kk
DataLink
DataLink
DataLink
DataLink
DataLink
DataLink
DataLink
Application
Presentation
Session
Transport
Network
DataLink
Physical
7
6
5
4
3
2
1
21interface
32interface
43interface
54interface
65interface
76interface
DataLink
DataLink
DataLink
DataLink
DataLink
DataLink
DataLink
Application
Presentation
Session
Transport
Network
DataLink
Physical
7
6
5
4
3
2
1
21interface
32interface
43interface
54interface
65interface
76interface
N/W N/W
DLL DLL
Phy Phy
Peerto
peer
protocol
(7
th
layer)
Peertopeerprotocol(6thlayer)
Peerto
peer
protocol
(5th
layer)
Peertopeerprotocol(4thlayer)
3rd 3rd 3rd
2nd
2nd
2nd
1st 1st 1st
Device
A
Device
B
Interactionbetweenlayers
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OSIReferencemodelOSIReferencemodel
Interlayercommunication
Interlayer
communication
Dataencapsulation
Horizontal
communication,
vertical
communication
Horizontal
communication,
vertical
communication
physicallayer;datalinklayer;networklayer;transport
layer; sessionlayer;presentationlayer; applicationlayer.
TCP/IP
Reference
model
Link;
Internet;
Transport;
Application
layer.
ComparisonoftheOSIandTCP/IPreferencemodels
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DataEncapsulationApplication
Data
Application
Data
Transport
header
Application
Data
Transport
header
Network
header
ApplicationData
Transportheader
Network
header
DataLink
header
DataLink
footer
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OSIReferencemodelOSIReferencemodel
Interlayercommunication
Interlayer
communication
DataencapsulationDataencapsulation
Horizontalcommunication,verticalcommunication
physicallayer;datalinklayer;networklayer;transport
layer; sessionlayer;presentationlayer; applicationlayer.
TCP/IP
Reference
model
Link;
Internet;
Transport;
Application
layer.
ComparisonoftheOSIandTCP/IPreferencemodels
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Application
Presentation
Session
Transport
Network
DataLink
Physical
7
6
5
4
3
2
1
Application
Presentation
Session
Transport
Network
DataLink
Physical
7
6
5
4
3
2
1
Horizontal andVerticalcommunication
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D7
D6H6
D5
D4
H4
D3H3
H7
D2H2
0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 0 0 0 0 1 0 0 0 0 010
T2
H5
Transmissionmedium
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D7
D6H6
D5
D4
H4
D3H3
H7
D2H2
0 1 0 1 0 1 0 1 0 1 0 1 1 0 1 0 1 0 0 0 0 0 1 0 0 0 0 010
T2
H5
As each block of
data
reaches
the
next higher layer,
the headers and
trailersattached
to
it
atthecorresponding
sending layer are
removed
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OSIReferencemodelOSIReferencemodel
Interlayercommunication
Interlayer
communication
DataencapsulationDataencapsulation
Horizontalcommunication,verticalcommunicationHorizontalcommunication,verticalcommunication
physicallayer;datalinklayer;networklayer;transport
layer; sessionlayer;presentationlayer; applicationlayer.
TCP/IP
Reference
model
Link;
Internet;
Transport;
Application
layer.
ComparisonoftheOSIandTCP/IPreferencemodels
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Physical L ayer
PhysicalTransmission
Medium
101010000001
L2data
Physical Layer
101010000001
L2data
Thislayertransmitstheunstructured,rawbitstreamoveraphysicalmedium
PhysicalLayer
It
deals
with
the
mechanical
and
electrical
specifications
of
the
interface
and
transmissionmedium.FromDLL ToDLL
Thephysicallayerisconcernwith:
Physicalcharacteristicsofinterfacesandmedium
Representationof
bits
Line
configuration
Transmissionmode Synchronizationofbits
Physicaltopology
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L3data
101010000000010
T2 Data H2
Sendsdataframesfromthenetworklayertothephysicallayer
DataLinkLayer
Thedata
link
layer
is
responsible
for
providing
error
free
transfer
of
these
frames
fromonecomputertoanotherthroughthephysicallayer.
FromN/Wlayer ToN/Wlayer
Specificresponsibilities
of
the
data
link
layer
:
1.Framing 2.Physicaladdressing 3.Flowcontrol
4.Errorcontrol
L3data
101010000000010
T2 Data H2
Tophysicallayer Fromphysicallayer
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1.Itisresponsibleforaddressingmessagesandtranslatinglogicaladdressesand
namesinto
physical
addresses.
NetworkLayer
2.Thislayeralsodeterminestheroutefromthesourcetothedestinationcomputer.
FromTransportlayer ToTransportlayer
SpecificresponsibilitiesoftheNetworklayer:
1.Logical
addressing
2.
Routing
ToDataLinklayer FromDataLinklayer
L4 data
H3
L3 data
L4 data
H3
L3 data
4.Italsomanagestrafficproblemsonthenetwork,suchasswitchingandroutingof
packetsandcontrollingthecongestionofdata.
3.Itdetermineswhichpaththedatashouldtakebasedonnetworkconditions,priorityof
service,andotherfactors.
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1.providesanadditionalconnectionlevelbeneaththesessionlayer
TransportLayer
2.It
ensures
that
packets
are
delivered
error
free,
in
sequence,
and
without
losses
or
duplications..FromSessionlayer ToSessionlayer
SpecificresponsibilitiesoftheTransportlayer:
1.Segmentationandreassembly 2.Connectioncontrol
ToN/Wlayer FromN/Wlayer
L5 data
H4 H4 H4
L4dataL4dataL4data
L5 data
H4 H4 H4
L4dataL4dataL4data
3.Flow
control
4.
Error
control
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1. allows two applications on different computers to open, use, and close a
connectioncalled
asession.
SessionLayer
2. It performs namerecognition and other functions, such as security, that are
neededtoallowtwoapplicationstocommunicateoverthenetwork.
FromPresentation
layer
To
Session
layer
ToTransportlayer FromTransportlayer
3. It performs namerecognition and other functions, such as security, that are
needed
to
allow
two
applications
to
communicate
over
the
network.
4.Thesessionlayersynchronizesusertasksbyplacingcheckpointsinthedatastream.
5.Thislayeralsoimplementsdialogcontrolbetweencommunicatingprocesses,such
asregulatingwhichsidetransmits,when,andforhowlong
H5
syn syn syn
H5
syn syn syn
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SpecificresponsibilitiesoftheSessionlayer:
1.DialogControl
2.Synchronization
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1. It defines the format used to exchange data among networked
computers.
PresentationLayer
2. It is concerned with the syntax and semantics of the information
exchangedbetweentwocomputers.
FromApplicationlayer ToApplicationlayer
Tosession
layer
From
session
layer
3. The presentation layer is responsible for converting protocols,
translatingthedata,encryptingthedata,changingorconvertingthecharacterset,andexpandinggraphicscommands
4.Italsomanagesdatacompressiontoreducethenumberofbitsthat
needto
be
transmitted.
H6 Data H6 Data
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SpecificresponsibilitiesofthePresentationlayer:
1.Translation
2.Encryption
3.Compression
Conversion from sender dependant format into a common format at sender and at
receiver change of common format into its receiver format takes place by
presentationlayer.
Thesendertransformstheoriginalinformationtoanotherandsendstheresulting
messageoutoverthenetwork,whichhandlesbypresentationlayer.
Itreducesthenumberofbitstobetransmitted.
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1. This layer relates to the services that directly support user
applications,
such
as
software
for
file
transfers,
database
access,
andemail.
ApplicationLayer
User User
ToPresentationlayer FromPresentationlayer
2. Applicationlayer protocols can be programs in themselves, such
as
File
Transfer
Protocol
(FTP),
or
they
can
be
used
by
otherprograms, such as Simple Mail Transfer Protocol (SMTP), used by
mostemailprograms,toredirectdatatothenetwork.
H7 Data
X.500 FTAM X.400...
Message H7 Data
X.500 FTAM X.400...
Message
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SpecificresponsibilitiesoftheApplicationlayer:
1.NetworkvirtualTerminal
2.Filetransfer,accessandmanagement(FTAM)
3.Mail
services
Itallowsausertologontoaremotehost.
Itallowsausertoaccessfiles inaremotecomputer,toreceivefilesfroma
remotecomputerandtomanageandcontrolfilesinaremotecomputer.
Itprovidesthebasisforemailforwardingandstorage.
4.Directoryservices
It provides distributed data sources and access for global informationaboutvariousobjectsandservices.
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Summaryofdutiesforeachlayer
Application
Presentation
Session
Transport
Network
DataLink
Physical
ToAllow
access
to
networkresourcesToTranslate,encrypt,
andcompressdata
Toestablish,
manage
andterminatesessionsToprovidereliableprocessto
processmessagedelivery&error
recoveryTomovepacketsfrom
sourcetodestinationToorganizebitsinto
framesTotransmitbitsovera
medium
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OSIReferencemodel
Interlayercommunication
Dataencapsulation
Horizontalcommunication,verticalcommunication
physicallayer;datalinklayer;networklayer;transport
layer; sessionlayer;presentationlayer; applicationlayer.
TCP/IPReferencemodelLink;Internet;Transport;Application
layer.
ComparisonoftheOSIandTCP/IPreferencemodels
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Application
Presentation
Session
Transport
Network
DataLink
Physical
Application
Transport
Internetlayer
N/Waccesslayer
N/W
interface
OR
Link
TCP/IPTransmissionControlProtocolInternetProtocol
It is an industrystandard suite of protocols that provide
communicationsinaheterogeneousenvironment.
TCP/IPalsosupports routingand iscommonlyusedasan
internetworkingprotocol.
TCP/IP is broken
intothefourlayers
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SMTP FTP DNS HTTP TELNET
Application
Applications
Presentation
Session
TCP
UDP
Transport
Internet ICMP IP ARP RARP
Protocolsspecifictotheunderlyingphysicalmedia
usedfordatacommunicationatthehardwarelevel
DataLink
Physical
LinkLayer
TCP/IPTransmissionControlProtocolInternetProtocol
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N/WaccesslayerorN/Winterface
Thenetwork interface layer, corresponding to the physical anddatalink layersoftheOSIreferencemodel,communicatesdirectly
withthenetwork.
It provides the interface between the network architecture (such
astoken
ring,
Ethernet)
and
the
Internet
layer.
Internetlayer
TheInternet layer, corresponding to the network layer of the OSI
reference model, uses several protocols for routing and delivering
packets.
Several
protocols
work
within
the
Internet
layer.
Internet ICMP IP ARP RARP
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1.InternetProtocol(IP)
InternetProtocol(IP) isapacketswitchedprotocolthatperformsaddressing
and
route
selection.
IP is a connectionless protocol and sends packets without
expectingthereceivinghosttoacknowledgereceipt.
IPisresponsibleforpacketassemblyanddisassembly
2. AddressResolutionProtocol(ARP)
Before an IP packet can be forwarded to another host, the
hardwareaddressofthereceivingmachinemustbeknown.
TheARP
determines
hardware
address
(MAC
addresses)
that
correspondtoanIPaddress.
3. ReverseAddressResolutionProtocol(RARP)
A
RARP
server
maintains
a
database
of
machine
numbers
in
theform of an ARP table (or cache) which is created by the system
administrator.
The RARP protocol provides an IP number to a requesting
hardwareaddress.
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4. InternetControlMessageProtocol(ICMP)
TheICMP
is
used
by
IP
and
higher
level
protocols
to
send
and
receivestatusreportsaboutinformationbeingtransmitted.
TransportLayer
It
is
responsible
for
establishing
and
maintaining
endto
end
communicationbetweentwohosts.
The transport layer provides acknowledgment of receipt, flow
control,and
sequencing
of
packets.
Italsohandlesretransmissionsofpackets.
The transport layer can use either TCP or User Datagram Protocol (UDP)
protocolsdepending
on
the
requirements
of
the
transmission.
TCP UDPTransport
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1.TransmissionControlProtocol(TCP)
The TCP is responsible for the reliable transmission of data from
onenode
to
another.
It is a connectionbased protocol and establishes a connection,
betweentwomachinesbeforeanydataistransferred.
2.User
Datagram
Protocol
(UDP)
Aconnectionlessprotocol,theUDP,isresponsibleforendtoend
transmissionofdata.
UDP does not establish a connection, it attempts to send the
dataand
to
verify
that
the
destination
host
actually
receives
the
data.
UDP is best used to send small amounts of data for which
guaranteeddelivery
is
not
required.
ApplicationLayer
Correspondingtothesession,presentation,andapplicationlayers
of the OSI reference model, the application layer connectsapplications
to
the
network.
SMTP FTP DNS HTTP TELNET
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OSIReferencemodel
Interlayercommunication
Dataencapsulation
Horizontalcommunication,verticalcommunication
physicallayer;datalinklayer;networklayer;transport
layer; sessionlayer;presentationlayer; applicationlayer.
TCP/IPReferencemodelLink;Internet;Transport;Application
layer.
ComparisonoftheOSIandTCP/IPreferencemodels
i b & /
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ComparisonbetweenOSI&TCP/IP
TCP/IP
also
supports
routing
and
is
commonly
used
as
an
internetworkingprotocol.
Application
Presentation
Session
Transport
Network
DataLink
Physical
7
6
5
4
3
2
1
Application
Transport
Internetlayer
N/Waccesslayer
N/Winterface
TCP/IPOSIReferenceModel
4
3
2
1
TCP/IP OSI Reference Model
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TCP/IP OSIReferenceModel
Defined after the
adventof
Internet
Defined before the
adventof
Internet
1. 1.
Service interface &
protocols were not
clearlydistinguished
Service interface &
protocolswereclearly
distinguished
2. 2.
TCP/IPsupports
internetworking
OSIdoesnotsupports
internetworking3. 3.
Looselylayered
Strict
layering
4. 4.Protocol dependent
standard
Protocolindependent
standard
5. 5.
Morecredible
Less
credible
6. 6.TCP reliably delivers
packets, IP does not
reliablydeliver packets
All packets are
reliably
delivered
7. 7.
Comparison between TCP & UDP
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ComparisonbetweenTCP&UDP
TCP UDP
Itisconnectionoriented,
nodatacorruptionwhile
datatransfer
It is connectionless, may
be data corruption while
datatransfer
Factor
Reliability
Messagearrives
in
order
No
order
message
Order
If order miss then it
requirestobebutback
No ordering of message,
notrackingconnection
Heavy/light
weight
Dataisreadasastream.
There may be multiple
packetperreadcall
Packets are individually,
onepacketpercall
Streaming/
datagram
www, email, FTP, HTTP,
TELNET,SMTPetc.
DNS,VOIP,DHCP,NFSExample