OSI Model

1. University of Education Lahore Multan
(campus)
presented by :
Muhammad Shakeel
Topic Name :
OSI Model

2. What is the OSI Model?:
OSI stands for open system interconnection .The
open systems interconnection (OSI) model is a conceptual model created by the
International Organization for Standardization which enables diverse
communication systems to communicate using standard protocols.
The OSI provides a standard for different computer systems to be able to
communicate with each other.
This model is called OSI (Open Systems Interconnection) it means , it is a
framework for transmitting messages between any two entities in a network.
OSI consists of seven layers.
Each layer should perform a well defined function.

4. Physical Layer :
It is the bottom layer of OSI Model. It is responsible for
the actual physical connection between the devices. Such physical connection
may be made by using twisted pair cable.
Function of Physical Layer :
• Transforming bits into signals
• It defines the transmission rate.
• It provides physical topologies
• It can use different techniques of multiplexing.

5. Data Link Layer :
The data link layer is very similar to the network layer, except the
data link layer facilitates data transfer between two devices on the same network.
The data link layer takes packets from the network layer and breaks them into
smaller pieces called frames.
It Consists of two layers:
Logical Link Control : It deals with protocols, flow-control, and error
control
Media Access Control : It deals with actual control of media

6. Functionality of Data-link Layer :
Framing:
Data-link layer takes packets from Network Layer and encapsulates them into
Frames . Then, it sends each frame bit-by-bit on the hardware. At receiver’ end, data
link layer picks up signals from hardware and assembles them into frames.
Addressing:
Data-link layer provides layer-2 hardware addressing mechanism. Hardware address
is assumed to be unique on the link. It is encoded into hardware at the time of
manufacturing.
Synchronization:
When data frames are sent on the link, both machines must be synchronized in
order to transfer to take place.

7. •Error Control
Sometimes signals may have encountered problem in transition and the bits are
flipped . These errors are detected and attempted to recover actual data bits. It also
provides error reporting mechanism to the sender.
•Flow Control
Stations on same link may have different speed or capacity. Data-link layer ensures
flow control that enables both machine to exchange data on same speed.

8. Network layer :
The network layer is responsible for facilitating data transfer
between two different networks. If the two devices communicating are on the same
network, then the network layer is unnecessary.
It Handles the routing and sending of data between different networks. The most
important protocols at this layer are IP and ICMP.
Function of network layer:
Internetworking: It provides Internetworking.
Logical Addressing : When packet is sent outside the network, N/W layer
adds Logical (network) address of the sender & receiver to each packet.

9. Routing :
• The network layer is responsible for routing packets from the source host
to the destination host. The routes can be based upon static tables that are rarely
changed; or they can be automatically updated depending upon network
conditions.

10. THANKS