networking models osi model created by international ... · layer functions 7 application 6...

© 1999, Cisco Systems, Inc.www.cisco.com

Networking ModelsOSI Model

Created by International Organization StandardizationPrepared by

Agha Mohammad HaidariNetwork Manager

ICT DirectorateMinistry of Communication & IT

Email : [email protected]#0700148122

Networking ModelsOSI Model

Created by International Organization StandardizationPrepared by

Agha Mohammad HaidariNetwork Manager

ICT DirectorateMinistry of Communication & IT

Email : [email protected]#0700148122

2-2CSE: Networking Fundamentals—OSI Model © 1999, Cisco Systems, Inc.www.cisco.com

OSI ModelOSI Model

• The early development of networks was disorganized in many ways. Theearly 1980s saw tremendous increases in the number and size ofnetworks. As companies realized the advantages of using networkingtechnology, networks were added or expanded almost as rapidly as newnetwork technologies were introduced.

• By the mid-1980s, these companies began to experience problems fromthe rapid expansion. Just as people who do not speak the same languagehave difficulty communicating with each other, it was difficult for networksthat used different specifications and implementations to exchangeinformation. The same problem occurred with the companies thatdeveloped private or proprietary networking technologies. Proprietarymeans that one or a small group of companies controls all usage of thetechnology. Networking technologies strictly following proprietary rulescould not communicate with technologies that followed differentproprietary rules


OSI ModelOSI Model

• The Open System Interconnection (OSI) reference model released in1984 was the descriptive network model that the ISO created. Itprovided vendors with a set of standards that ensured greatercompatibility and interoperability among various network technologiesproduced by companies around the world.


OSI ModelOSI Model

Dividing the network into seven layers provides the following advantages:• It breaks network communication into smaller, more manageable parts.

• It standardizes network components to allow multiple vendor development and support.

• It allows different types of network hardware and software to communicate with each other.

• It prevents changes in one layer from affecting other layers.

• It divides network communication into smaller parts to make learning it easier to understand


Seven Layers of theOSI Reference ModelSeven Layers of the

OSI Reference Model

• Layer 7: Application• Layer 6: Presentation• Layer 5: Session• Layer 4: Transport• Layer 3: Network• Layer 2: Data link• Layer 1: Physical


Why a Layered Network Model?Why a Layered Network Model?

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

• Reduces complexity (one bigproblem to seven smallerones)

• Standardizes interfaces• Facilitates modular

engineering• Simplifies teaching and

learning


Devices Function at LayersDevices Function at Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

NIC Card

Hub


Host LayersHost Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Host layers:Host layers: Provideaccurate data delivery betweencomputers}


Media LayersMedia Layers

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Host layers:Host layers: Provideaccurate data delivery betweencomputers

Media layers:Media layers: Controlphysical delivery of messagesover the network}

}


Layer FunctionsLayer Functions

Provides network services to applicationprocesses (such as electronic mail, filetransfer,

7 Application



Network services to applicationsNetwork services to applications

• Ensures data is readable byreceiving system

• Format of data• Data structures• Negotiates data transfer

syntax for application layer

7 Application

6 Presentation Data representation



Inter-host communication• Establishes, manages, and

terminates sessions betweenapplications

7 Application

6 Presentation

5 Session


Data representationData representation



7 Application

6 Presentation

5 Session

Transport4

InterInter--host communicationhost communication



End-to-end connection reliability• Concerned with data transport

issues between hosts• Data transport reliability• Establishes, maintains, and

terminates virtual circuits• Fault detection and recovery• Information flow control



7 Application

6 Presentation

5 Session

Transport4

Network3




EndEnd--toto--end connection reliabilityend connection reliability

Addresses and best path• Provides connectivity and path

selection between two endsystems

• Domain of routing


Layer FunctionsLayer Functions7 Application

6 Presentation

5 Session

Transport4

Network3

Data Link2





Addresses and best pathAddresses and best path

Access to media• Provides reliable transfer of data

across media• Physical addressing, network

topology, error notification, flowcontrol


Layer FunctionsLayer Functions7 Application

6 Presentation

5 Session

Transport4

Network3

Data Link2

Physical1





Addresses and best pathAddresses and best path

Access to mediaAccess to media

Binary transmission• Wires, connectors, voltages,

data rates


7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Host A

Peer-to-Peer CommunicationsPeer-to-Peer Communications

Application

Presentation

Session

Transport

Network

Data Link

PhysicalBits

Frames

Packets

Segments

Host B


Data EncapsulationData Encapsulation

Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Host A Host B

Data} {



Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Data} {DataNetwork

Header

Host A Host B



Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Data} {DataNetwork

Header

FrameHeader

FrameTrailer

DataNetworkHeader

Host A Host B



Application

Presentation

Session

Transport

Network

Physical

Data Link

Application

Presentation

Session

Transport

Network

Physical

Data Link

Data} {DataNetwork

Header

FrameHeader

FrameTrailer

DataNetworkHeader

0101101010110001

Host A Host B


The Application (Upper) LayersThe Application (Upper) Layers• Application

– User interface– Examples – Telnet, HTTP

• Presentation– How data is presented– Special processing, such as encryption– Examples – FTP enables you to choose binary or ASCII transfer.

• Session– Keeping different applications’ data separate

– defines how to start, control, and end conversations (calledsessions).

– Examples – Operating system/application access scheduling


The Data-Flow (Lower) LayersThe Data-Flow (Lower) Layers

• Transport– Focuses on issues related to data delivery– Reliable or unreliable delivery– Segmentation of large application data– Error correction before transmit– Examples: TCP, UDP,

• Network– This layer defines end-to-end delivery of packets.– Provide logical addressing which routers use for path determination– Examples: IP,


The Lower Layers (cont.)The Lower Layers (cont.)

• Data link– These protocols are necessarily concerned with the type of media– Combines bits into bytes and bytes into frames– Access to media using MAC address– Error detection not correction

• Physical– Moves bits between devices– Specifies voltage, wire speed, and pinout cable .


The Data-Flow (Lower) LayersThe Data-Flow (Lower) Layers

• Transport– Focuses on issues related to data delivery– Reliable or unreliable delivery– Segmentation of large application data– Error correction before transmi

• Network– This layer defines end-to-end delivery of packets.– Provide logical addressing which routers use for path determination


Network Layer: Path DeterminationNetwork Layer: Path Determination

Which Path?Which Path?

• Layer 3 functions to find the bestpath through the internetwork


Network Layer: Communicate PathNetwork Layer: Communicate Path

1

2

3

4

5

6

7

89

10 11

• Addresses represent the path of mediaconnections

• Routing helps contain broadcasts


Transport LayerTransport Layer

• Segments upper-layer applications• Establishes an end-to-end connection• Sends segments from one end host to another• Optionally, ensures data reliability


Presentation LayerPresentation Layer

ASCIIEBCDICEncrypted

• Text• Data

login:

PICTTIFFJPEGGIF

• Graphics• Visual images

• Sound

• VideoMPEGQuickTime

MIDI

• Provides code formatting andconversion for applications


Application LayerApplication Layer

Word ProcessorPresentation GraphicsSpreadsheetDatabaseDesign/ManufacturingProject PlanningOthers

COMPUTERAPPLICATIONS

Electronic MailFile TransferRemote AccessClient-Server ProcessInformation LocationNetwork ManagementOthers

NETWORKAPPLICATIONS


The OSI ModelThe OSI Model

• Application – Think of browsers.• Presentation – Think of common data format.• Session – Think of dialogs and conversations.• Transport – Think of flow control and reliability.• Network – Think of path selection, routing, and logical addressing.• Data Link – Think of frames and media access control.• Physical – Think of signals and media.


History and Future of TCP/IPHistory and Future of TCP/IP

• The U.S. Department of Defense(DoD) created the TCP/IPreference model because itwanted a network that couldsurvive any conditions.

• Some of the layers in the TCP/IPmodel have the same name aslayers in the OSI model.


TCP/IP modelTCP/IP model

• Application layer

• Transport layer

• Internet layer

• Network access layer

The TCP/IP model has the following four layers


Similarities of the OSI and TCP/IPmodels

Similarities of the OSI and TCP/IPmodels

• Both have layers.

• Both have application layers, though they include very differentservices.

• Both have comparable transport and network layers.

• Networking professionals need to know both models.


Differences of the OSI and TCP/IPmodels

Differences of the OSI and TCP/IPmodels

• TCP/IP combines the presentation and session layer into its application layer.• TCP/IP combines the OSI data link and physical layers into one layer.• IP is called a network layer, or Layer 3, protocol. Similarly,• the TCP/IP transport layer defines many functions, including error recovery, as does the OSI• transport layer—so TCP is called a transport layer, or Layer 4, protocol.


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