DCCN PPTDCCN PPT ON ONOSI REFERNCE(7 OSI REFERNCE(7 LAYER)MODEL LAYER)MODEL

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An open system is a set of protocols that allow two different systems to communicate regardless of their

Open Systems Interconnection Open Systems Interconnection (OSI) it is a networking model which is fundamental to all communications between network devices

It is now the theoretical model for how communication takes place between network devices.

The OSI reference model is an arbitrary hierarchical stratification (layering) of computer networking functions. The stratification consists of seven layers.

The OSI Reference ModelThe OSI reference model consists of seven layers, not including layer 8, the

end user’s application, and layer 0 the physical transmission media.8. O/S or User Application

0. Physical Transmission Media

THE SEVEN OSI THE SEVEN OSI REFERENCE MODEL REFERENCE MODEL LAYERSLAYERS

LAYER 1: PHYSICALLAYER 1: PHYSICAL The physical layer deals with the physical The physical layer deals with the physical

characteristics of the transmission medium. characteristics of the transmission medium. and it sends the data in the form and it sends the data in the form

of raw bitsof raw bits It defines the electrical, mechanical, It defines the electrical, mechanical,

procedural, and functional specifications for procedural, and functional specifications for activating, maintaining, and deactivating the activating, maintaining, and deactivating the physical link between end systems. physical link between end systems.

. .

FUNCTIONS

It controls the define voltages and bit rates needed for transmission

This layer manages the interface between the computer and the network medium (coaxial cable, twisted pair)

It is the bottom layer of the OSI model

1.Signal encoding1.Signal encoding 2.Bit synchronization2.Bit synchronization 3.transmission type3.transmission type 4.topology4.topology 5.Transmission media5.Transmission media MultiplexingMultiplexing Interface 6. Bandwidth 7.Signal typeInterface 6. Bandwidth 7.Signal type

This layer takes the data frames (or) messages from the layer and provides their actual transmission

A message is a block statement such as ok (or) yes, which denotes positive (or) negative acknowledgement (or) request for repeating such as “come again” (or) pardon me .

At the sending end this layer handles conversion of data into raw formats that can be handled by the Physical Layer

Layer 2 : DATA LAYER

Data Link LayerData Link Layer

synchronizationsynchronization To take packets from the upper layer and To take packets from the upper layer and

converting them into framesconverting them into frames To take bits from lower and converting them into To take bits from lower and converting them into

packetspackets Error detection and controlError detection and control FramingFraming

010110110101

011000101110110000001

DATA LINK LAYER

LAYER 3: NETWORKLAYER 3: NETWORK

Defines end-to-end delivery of packets. Defines end-to-end delivery of packets. It receives the packets from transport It receives the packets from transport

layer and converts them into frameslayer and converts them into frames Defines how routing works and how Defines how routing works and how

routes are learned so that the packets routes are learned so that the packets can be delivered. can be delivered.

It is responsible for sending the data to It is responsible for sending the data to destination node by choosing the data destination node by choosing the data

NETWORK LAYER

Establishing the connection

Releasing the connections

Sending the data

This layer also handles packet switching and network congestion control

LAYER 4: TRANSPORTLAYER 4: TRANSPORT

If once it receives the data from session If once it receives the data from session layer it splits the data into packets layer it splits the data into packets

After dividing it adds sequence to the After dividing it adds sequence to the packetspackets

It is responsible for error control and It is responsible for error control and flow controlflow control

The Transport LayerThe Transport Layer DIAGRAMDIAGRAM

ERROR CONTROL: while transmitting the data if they are errors in the data which is been sent to the destination node it detects and controls the error and resends the data to the node

FLOW CNTROL: when the data is sent . The form of data sending should be maintained currently for acknowledgement

LAYER 5: SESSION LAYERLAYER 5: SESSION LAYER

When once the data is received from the presentation layer it is When once the data is received from the presentation layer it is converted in the form of sessions converted in the form of sessions

Again this sessions are divided into sub sessions Again this sessions are divided into sub sessions It avoids the retransmission by adding the checking point It avoids the retransmission by adding the checking point

feature if the system craches (or) power failures last checking feature if the system craches (or) power failures last checking point substation re-trasnmitts the left data but not the entire point substation re-trasnmitts the left data but not the entire data againdata again

At destination side it receives the data from the transport layer At destination side it receives the data from the transport layer and handovers the data to the presentation layerand handovers the data to the presentation layer

Whenever it is divided into substations it adds the sequence Whenever it is divided into substations it adds the sequence numbernumber

The Session LayerThe Session Layer

Responsibilities:Responsibilities: establishes, manages, and terminates establishes, manages, and terminates

sessions between applications.sessions between applications. service location lookupservice location lookup

Responsible for security and access control to session information (via session participant identification)

Responsible for synchronization services

(checkpoints)

LAYER 6: PRESENTATIONLAYER 6: PRESENTATION

It provides compression of dataIt provides compression of data It is concerned with Semantics and It is concerned with Semantics and

syntax of the informationsyntax of the information Provides compression of dataProvides compression of data It is responsible for It is responsible for Data EncodingData Encoding Data CompressionData Compression Data conversionData conversion

The Presentation LayerThe Presentation Layer

Responsibilities:Responsibilities: data encryptiondata encryption data compressiondata compression data conversiondata conversion

PRESENTATION LAYER

Data Encoding: The data is encoded i.e if one node (source node) supports ASCII format, Destination node may support UNICODE format and at this time the data is transmitted in the form of UNCODE even the source node supports ASCII format

Compression: The data is compressed before sending it to the destination node, here the data is compressed in the destination layer

This layer is also responsible for certain protocol conversions, data encryption/decryption, or data compression/decompression.

The top layer of the OSI model

The container which contains various types of protocols i.e www, http is called application layer

If once it is connected to the protocol it handovers to the presentation layer

LAYER 7: APPLICATIONLAYER 7: APPLICATION

APPLICATION LAYER

The application layer is the closest to the user.The application layer is the closest to the user.

It provides network access to the user. It provides network access to the user. It differs from the other layers in that it does It differs from the other layers in that it does

not provide services to any other OSI layer, not provide services to any other OSI layer, but rather, only to applications outside the OSI but rather, only to applications outside the OSI model. model.

Examples of such applications are spreadsheet Examples of such applications are spreadsheet programs, word processing programs, and programs, word processing programs, and bank terminal programs. bank terminal programs.

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

7 Application

6 Presentation

5 Session

4 Transport

3 Network

2 Data Link

1 Physical

Tran

smission M

edia

UserApplication

UserApplication

Sending Computer Receiving Computer

EXAMPLE FOR OSI REFERENCE MODEL FUNCTIONING