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OSI Layers

Presented By

bhuvanesh kumar

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OSI means Open System Interconnect model.

Developed by the International Organization for Standardization in1974.

It consists of seven layers.

Each layer has a different but specific processing function.

OSI Model

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OSI Model Layers

Application

Presentation

Session

Transport

Network

Data Link

Physical

Layer - 7

Layer - 6

Layer - 5

Layer - 4

Layer - 3

Layer - 2

Layer - 1

Upper Layeror

Software Layer

Lower LayerorHardware Layer

Heart of OSI

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Data flow from Transport Layer

Data

Data

Data

DataTH

Segment

Application

Presentation

Session

Transport

Network

Data Link

Physical

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Network Layer

Network Layer isresponsible for providing bestpath for data to reach thedestination. Logical Addressingworks on this layer. Router is aNetwork Layer device.

It is divided into two parts Routed Protocols

e.g. IP, IPX, Apple Talk. Routing Protocols

e.g. RIP, IGRP, OSPF, EIGRP

Application

Presentation

Session

Transport

Network

Data Link

Physical

Network

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Routed Protocols

Hello!

How areyou ?

192.168.1.1 192.168.1.2

A B

Segment

Segment

Source IP192.168.1.1

Destination IP192.168.1.2

Source IP192.168.1.1

Destination IP192.168.1.2

Segment

Hello!

How areyou ?

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Routing Protocols

A

www.zoomgroup.com

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Data flow from Network Layer

Data

Data

Data

Segment

Segment

NH

e.g. Router

Packet

Application

Presentation

Session

Transport

Network

Data Link

Physical

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Datalink Layer

Datalink Layer isdivided into two Sub Layers :

LLC Logical Link ControlIt talks about Wan protocols e.g.

PPP, HDLC, Frame-relay

MAC Media Access ControlIt talks about Physical Address.It is a 48 bit address i.e. 12 digit

Hexadecimal Number.It is also responsible for ErrorDetectionDevices working on Data LinkLayer are Switch, Bridge, NIC.

Application

Presentation

Session

Transport

Network

Data Link

Physical

Data Link

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Error Detection CRC Check

Hello!How are

you ?

Packet

Packet

Source MAC00-20-18-C0-07-71

Destination MAC00-20-18-C0-07-72

000003243422222896965543499323434349943446323111143333300000324342222289696554349932343434994344632311114Error Detected

192.168.1.100-20-18-C0-07-71

192.168.1.200-20-18-C0-07-72

A B

PC-ACRC No. 33333

PC-BCRC No. 11114Error Detected

For Error Correction

Contact Source Transport layer

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Error Detection CRC Check

Packet

Packet

Source MAC00-20-18-C0-07-71

Destination MAC00-20-18-C0-07-72

00000324342222289696554349932343434994344632311114202020000032434222228969655434993234343499434463231111420202

Source MAC00-20-18-C0-07-71

Destination MAC00-20-18-C0-07-72

Packet

Hello!How are

you ?

192.168.1.100-20-18-C0-07-71

192.168.1.200-20-18-C0-07-72

A B

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e.g. Switch

Data flow from Data Link Layer

Data

Data

Data

Segment

DH

Packet

DT

Application

Presentation

Session

Transport

Network

Data Link

Physical

PacketPacketFrame

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Physical Layer

Physical Layer isresponsible for electrical,mechanical and procedural checks.Data will be converted into Binary(i.e) 0s & 1s. Data will be in theform of electrical pulses if it is

Coaxial or Twisted Pair cable and inthe form of Light if it is Fiber OpticCable.

Devices working at Physical Layerare Hubs, Repeaters, Cables,Modems etc.

Application

Presentation

Session

Transport

Network

Data Link

PhysicalPhysical

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Physical Layer Example

Frame

Frame

10101010101010101010101010101010

Frame

Hello!

How areyou ?

A B01010110101010101010101011010101101010101010101010010101101010101010101010110101011010101010101010100101011010101010101010101

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Data flow from Physical Layer

Data

Data

Data

Segment

Packet

Frame

Bits

e.g. Hub

Application

Presentation

Session

Transport

Network

Data Link

Physical

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Segment

Packet

Frame

A B

Packet

Data

Data

Data

Bits

Data

Segment

Data Encapsulation & De-capsulation

Packet

Data

Data

Data

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

PhysicalBits

DH DT

NH

THSegment

Packet

DT PacketDH DTDH

NH Segment NH

TH Data TH

Frame Packet

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Application

Transport

Internet

NetworkAccess

Comparing OSI with TCP/IP Layers

OSI Layers TCP/IP Layers

Application

Presentation

Session

Transport

Network

Data Link

Physical

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