OSI_Layer.ppt

CCNACisco Certified Network Associate

640-802

www.arabhardware.net

Mohammedsn

علما ” ” زدني رب قل و تعالي قال

OSI 7 layerOSI 7 layerOSI Open System InterconnectionOSI Open System InterconnectionWe want the system to be standard to can We want the system to be standard to can

any one use itany one use it ISO International Standard Organization ISO International Standard Organization Make standarization to main task for Make standarization to main task for

operation ( IEEE)operation ( IEEE)


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33

OSI Model OverviewOSI Model Overview

Data Flow Layers

Transport Layer

Data Link

Network Layer

Physical

Application (Upper) Layers

Session

Presentation

Application


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7- Application 7- Application LayerLayer

HTTP : Browsing protocolHTTP : Browsing protocolFTP : File Transfer Protocol FTP : File Transfer Protocol TFTP : Trivial FTPTFTP : Trivial FTPTelnet : Remote access protocolTelnet : Remote access protocolSMTP : Simple Mail Transfer protocol SMTP : Simple Mail Transfer protocol SNMP : Simple Network Management SNMP : Simple Network Management

ProtocolProtocol


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66 - -presentation layerpresentation layer

Format of data Format of data Compression & decompression of dataCompression & decompression of dataEncoding & decoding of data Encoding & decoding of data

Such ac ASCII code ( 8bit) , EBCDIC code Such ac ASCII code ( 8bit) , EBCDIC code (5bit) (5bit)


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55 - -session layersession layer Set a logical connection ( session) Set a logical connection ( session)

between different applicationbetween different applicationSpecifies communication mode Specifies communication mode ( simple - Half duplex – full duplex ) ( simple - Half duplex – full duplex )


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44 - -Transport layerTransport layer

Flow control Flow control

Error recovery Error recovery


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Flow controlFlow control

Pc1 Pc2

stop

Go on

BufferingCongestion avoidence


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WindowingWindowing

Sender Receiver


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WindowingWindowing

Window size = 3Send 2

Sender ReceiverWindow size = 3Send 1



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WindowingWindowing

Sender Window size = 3Send 1


ACK 3Window size = 2

Packet 3 isDropped

Receiver


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WindowingWindowing




Packet 3 isDropped



Receiver


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WindowingWindowing




Packet 3 isDropped




Receiver


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TCP Sequence and TCP Sequence and Acknowledgment NumbersAcknowledgment NumbersSource

PortDest.Port

…Sequence#

Acknowledgement#

Source Dest. Seq. Ack.1028 23 10 1

I justsent #10.


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TCP Sequence and TCP Sequence and Acknowledgment NumbersAcknowledgment Numbers

I just got #10,now I need #11.

SourcePort

Dest.Port …Sequence

#Acknowledgement

#

1028 23

Source Dest.

1010

Seq.

1

Ack.

102823

Source Dest.

1111

Seq.

1

Ack.

I justsent #10.


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PortDest.Port …Sequence

#Acknowledgement

#

1028 23

Source Dest.

1111

Seq.

2

Ack.

1028 23

Source Dest.

1010

Seq.

1

Ack.

102823

Source Dest.

1111

Seq.

1

Ack.

I just got #10,now I need #11.

I justsent #11.


Mohammedsn


PortDest.Port …Sequence

#Acknowledgement

#

1028 23

Source Dest.

1111

Seq.

2

Ack.

1028 23

Source Dest.

1010

Seq.

1

Ack.

102823

Source Dest.

1111

Seq.

1

Ack.

102823

Source Dest.

1212

Seq.

2

Ack.

I just got #11,now I need #12

I justsent #11.

Type of protocol at transport layerType of protocol at transport layer

TCP (connection oriented protocol)TCP (connection oriented protocol)

It must establish session before transmit the It must establish session before transmit the data , make recovery&controldata , make recovery&control

UDP connectionless protocol no UDP connectionless protocol no session,no recovery&no control session,no recovery&no control


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3-Network layer

1-routing 2-IP addressing


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22 - -Data linkData link 1- Arbitration : find the best time to send 1- Arbitration : find the best time to send

the data ( CSMA/CD & taken) the data ( CSMA/CD & taken)

Error detection Error detection 1- parity check : but very week1- parity check : but very week2-CRC : Depend on mathematical equation 2-CRC : Depend on mathematical equation


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Data link is divided into two sub Data link is divided into two sub layerlayer

802.3 MAC sub layer ( Media Access 802.3 MAC sub layer ( Media Access control) control)

802.2 LLC sub layer ( Logical Link Control) 802.2 LLC sub layer ( Logical Link Control)


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MAC address : hardware address

48 bit

24 bit ( vendor) 24 bit IEEE

LLC sub layerLLC sub layer

TCP/IP SPX/IPX


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Physical Layer: Physical Layer: Ethernet/802.3Ethernet/802.3

Hub

Hosts

Host

10Base2—Thin Ethernet10Base5—Thick Ethernet

10BaseT—Twisted Pair


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Encapsulating Data

Transport

Data Link

Physical

Network

Upper Layer Data

Upper Layer DataTCP Header

DataIP Header

DataLLC Header

0101110101001000010

DataMAC Header

Presentation

Application

Session

Segment

Packet

Bits

Frame

PDU

FCS

FCS

Upper Layer Data

De-encapsulating Data

LLC Hdr + IP + TCP + Upper Layer Data

MAC Header

IP + TCP + Upper Layer Data

LLC Header

TCP+ Upper Layer Data

IP Header

Upper Layer Data

TCP Header

0101110101001000010

Transport

Data Link

Physical

Network

Presentation

Application

Session

Network Device Domains

Hub Bridge Switch Router

Collision Domains:1 4 4 4

Broadcast Domains:1 1 1 4

Hubs Operate at Physical layer

A B C D

Physical

• All devices in the same collision domain• All devices in the same broadcast domain• Devices share the same bandwidth

ffff.ffff.ffff

• Each segment has its own collision domain• All segments are in the same broadcast domain

Data Link

Switches and Bridges Operate at Data Link Layer

OR1 2 3 1 24

Router Operate at Network layer


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255.255.255.255

Question

A B C DA B C D

Broadcast ??

collision ??


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Question

A B C DA B C D

Broadcast ??

collision ??


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Question

A B C DA B C D

Broadcast ??

collision ??


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ABCABC

QuestionBroadcast ?

?collision ??


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Hubs: One Collision DomainHubs: One Collision Domain

• More end stations means more collisions

• CSMA/CD is used

SwitchesSwitches

• Each segment has its own collision domain

• Broadcasts are forwarded to all segments

Memory

Switch

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OSI_Layer.ppt