1_osi_model.pps

7/29/2019 1_OSI_MODEL.pps

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OSI: Open System Interconnection .

Developed by the International Organization forStandardization in 1974.

There are seven layers in OSI reference Model .

process or role

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OSI Reference 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 Layer

or

Software Layer

Lower Layeror

Hardware Layer

Heart of OSI


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Application Layer

Application Layer isresponsible for providingNetworking Services to the user.It is also known as DesktopLayer. Identification of Servicesis done using Port Numbers.

Ports are Entry and Exit Pointsto the Layer

Total No. Ports 0 65535Reserved Ports 0 1023

Open Client Ports 1024 65535

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application


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Examples of Networking Services

Service Port No.

HTTP 80

FTP 21

SMTP 25

TELNET 23

TFTP 69


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Application

2180 25 6753 69

Data flow from Application Layer

Data

Presentation

Session

Transport

Network

Data Link

Physical


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Presentation Layer

Presentation Layer is

responsible for converting datainto standard format.

Examples : ASCII, EBCDIC, JPEG,MPEG, BMP, MIDI, WAV, MP3

Following tasks are perform atPresentation layer :

Encoding DecodingEncryption Decryption

Compression Decompression

Application

Presentation

Session

Transport

Network

Data Link

Physical

Presentation


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Data flow from Presentation Layer

Data

DataApplication

Presentation

Session

Transport

Network

Data Link

Physical


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Session Layer

Session Layer is responsible forestablishing, maintaining andterminating session.

Session ID works at Session Layer.

Examples :

RPC Remote Procedure CallSQL Structured Query Language

NFS Network File System

Application

Presentation

Session

Transport

Network

Data Link

Physical

Session


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Data flow from Session Layer

Data

Data

Data

Application

Presentation

Session

Transport

Network

Data Link

Physical


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Transport Layer

Transport Layer is

responsible for end-to-endconnectivity. It is also known asthe heart of OSI Layers.Following tasks are performed atthe Transport Layer : -

Identifying Service

Multiplexing & De-multiplexing

Segmentation

Sequencing & Reassembling

Error Correction

Flow Control

Application

Presentation

Session

Transport

Network

Data Link

Physical

Transport


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Identifying Service

Transmission Control

Protocol

Connection Oriented

Acknowledgement

Reliable

Slower Port No. 6

e.g. HTTP, FTP, SMTP

User Datagram

Protocol

Connection Less

No Acknowledgement

Unreliable

Faster Port No. 17

e.g. DNS, DHCP, TFTP

TCP UDP


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Application

Presentation

Session

Multiplexing & De-multiplexing

2180 25 6753 69

Transport

TCP - 6 UDP - 17

Network

Data Link

Physical


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Data flow from Transport Layer

Data

Data

Data

DataTHSegment

Application

Presentation

Session

Transport

Network

Data Link

Physical


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Network Layer

Network Layer is

responsible 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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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 is

divided into two Sub Layers :

LLC Logical Link Control

It talks about Wan protocols e.g.

PPP, HDLC, Frame-relay

MAC Media Access Control

It talks about Physical Address.It is a 48 bit address i.e. 12 digit

Hexadecimal Number.It is also responsible for ErrorDetection

Devices working on Data LinkLayer are Switch, Bridge, NIC.

Application

Presentation

Session

Transport

Network

Data Link

Physical

Data Link


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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 is

responsible 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 Layer

are Hubs, Repeaters, Cables,Modems etc.

Application

Presentation

Session

Transport

Network

Data Link

PhysicalPhysical


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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 DataTH

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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