OSI Layers

OSI LAYERS

Kashif Latif

OSI - THE MODEL A layer model (Open Systems

Interconnection) Each layer performs a subset of the

required communication functions Each layer relies on the next lower layer

to perform more primitive functions Each layer provides services to the next

higher layer Changes in one layer should not require

changes in other layers

LAYERS- MODEL

WHY LAYERS…?

A layered architecture allows us to discuss a well-defined ,specific part of a large and complex system.

Breaks down the complex operation of networking into simple elements.

Helps developers in developing software. It is also much easier to change the implementation

of the service provided by the layer. Helps in troubleshooting and identifying the problem. It provides a way to understand how an internet work

operates. Task broken into subtasks

REAL TIME EXAMPLE

PHYSICAL LAYER The physical layer is responsible for transmitting

individual bits from one node to the next. The physical layer defines Media type ,Connector

type and Signaling type . Physical layer defines the following characteristics of

interface between data transmission device (e.g. computer) and transmission medium or network.

Mechanical Electrical Functional Procedural

Representation of bits Data rates

PHYSICAL LAYER

DATA LINK LAYER Data link layer is responsible for activating,

maintaining and deactivating a reliable link between two nodes.

The data link layer is responsible for transmitting frames from one node to another. 1. Framing2. Physical Addressing3. Flow control4. Error control5. Access control

DATA LINK LAYER

NETWORK LAYER

The network layer is responsible for the delivery of packets from the original source to the final destination.

1. Data is in the form of Packets2. Logical (IP) Addressing 3. Routing4. Main protocols at this layer are IP ,ICMP ,ARP

NOTE

The network layer is responsible for the source to destination delivery of a packet possibly across multiple networks.

Where as the data link layer oversees the delivery of the packet between two systems on the same network.

NETWORK LAYER

TRANSPORT LAYER

The transport layer is responsible for delivery of a message from one process to another.

It defines:1. Reliable delivery of data2. Ordering of delivery3. Port addressing4. Segmentation and reassembly5. Connection control6. Flow control and Error control7. Main protocols are TCP and UDP

TRANSPORT LAYER

TRANSPORT LAYER

SESSION LAYER

This OSI layer, as the name implies:1. Establishes2. Maintains3. Ends sessions between nodes4. Manage transmit data

Dialog controller i.e. whether connection is half duplex or full duplex.

PRESENTATION LAYER

Defines the format of data being sent The presentation layer is designed to handle the

syntax and semantics of the information exchanged between two systems

Main functions of this layer are 1. Compression2. Encryption and Decryption

Some Examples of services used are listed below: 1. HTML (Hyper Text Markup Language)2. GIF (Graphics Interchange Format )3. JPEG (Joint Photographic Experts Group)4. ASCII (American Standard Code for Information

Interchange)

APPLICATION LAYER The application layer is responsible for

providing services to the user. The application layer enables the user to

access the network.1. Mail services2. File transfer and access3. Remote log-in4. Accessing the world wide web5. Main protocols at this layer are HTTP, SMTP,

SNMP, FTP, TELNET

APPLICATION LAYER

THANK YOU…!

Kashif Latif