Operating System Interface Layers

8/3/2019 Operating System Interface Layers

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OSI Layers

By- Manohar Prasad.



7 Layers:

Cli

ck to edit Master text styleSecond level● Third level● Fourth level● Fifth level

The Seven Layers of the OSI Modelcan be divided into two categories:•Upper Layer.•Lower Layer.

The Upper Layers of the OSI Modeldeal with application issues andare generally implemented only inSoftware.

The Lower Layers of the OSI Modelhandle data transport issues andare implemented in hardware andSoftware.

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1. Physical Layer:

The Physical Layer of the OSI Model defines connecter &

interface specifications, as well as medium requirements.Protocols at the Physical Layer accept frames from the DataLink Layer & transmit signals.

When receiving data, physical layer protocols detect &

accept signals and pass on to the Data Link Layer.

Connectivity devices such as Hubs and Repeaters operateat the Physical Layer.

Physical Layer protocols also set the data transmission

rate.




2. Data Link Layer:

The primary function of the Data Link Layer is to divide datareceived from the Network Layer into distinct frames that can

be transmitted by the Physical Layer.

The Data Link Layer is divided into two sublayers:

Ø The Upper sublayer of the Data Link Layer, called theLogical Link Control, provides an interface to the NetworkLayer protocols , manages flow control & issues requestsfor transmission of data.

Ø The Lower sublayer of the Data Link Layer, called theMedia Access Control manages access to the Physical

medium.

Ex. A Network Interface Card having MAC address.




3. Network Layer:

The primary function of the network layer is to

translate network address into their physicalcounter parts & decide how to route data fromthe sender to the receiver.

Each node has two types of addresses:(a) Network address (b) Physical address

Network layer protocols determine the path

from point A on one network to point B onanother network by:

(a)Delivery priorities (b)Network congestion.




4. Transport Layer

The transport layer accepts data from session

layer & manages the end-to-end delivery of data.It breaks large data units into multiple smaller units, called segments.

Generally, it is responsible for making sure thatthe data is delivered error-free & in proper sequence.

Some transport layer protocols known asconnection-oriented take steps to ensure that thedata arrives exactly as it was sent.

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5. Session Layer The session layer, provides various services, includingtracking the number of bytes that each end of the session has

acknowledged receiving from the other end of the session. Itallows applications functioning on devices to establish,manage, and terminate a dialog through a network. Sessionlayer functionality includes:

Virtual connection between application entities

Synchronization of data flow

Creation of dialog units

Connection parameter negotiations

Partitioning of services into functional groups

Acknowledgements of data received during a session

Retransmission of data if it is not received by a device




6. Presentation Layer The presentation layer, is responsible for how an applicationformats the data to be sent out onto the network. The

presentation layer allows an application to read (or understand) the message.

Examples of presentation layer functionality include:

• Encryption(such as the scrambling of passwords) anddecryption of a data for security.

• Compression and expansion of a data so that it travelsefficiently.

• Graphics formatting.• Content translation.

• System-specific translation.




7.Application Layer

The application layer, provides an interface for the end user

operating a device connected to a network.

This layer is what the user sees, in terms of loading anapplication (such as Web browser or e-mail); that is, thisapplication layer is the data the user views while using these

applications.Examples of application layer functionality include:

• Support for file transfers.

• Ability to print on a network.

• Electronic mail.

• Electronic messaging.

• Browsing the World Wide Web.




Thanks !11/23/11 Manohar Prasad. 1111

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