This document discusses the OSI model and its seven layers - physical, data link, network, transport, session, presentation and application layer. It describes the key functions and responsibilities of each layer. The physical layer deals with physical interfaces and encoding of data. The data link layer handles framing, addressing, error control and flow control. The network layer provides logical addressing and routing of packets across networks. Higher layers include the transport layer for process-to-process delivery, session layer for dialog control and synchronization, and presentation layer for translation, encryption/decryption and compression/decompression of data. The application layer supports various applications and user interfaces.

1. COMPUTER NETWORKS
CS8591
III V
CS8591
COMPUTER NETWORKS
UNIT NO 1
INTRODUCTION AND PHYSICAL LAYER
1.4 OSI MODEL
III V
CS8591
COMPUTER NETWORKS
(Common to CSE & IT)

2. COMPUTER NETWORKS - (Common to CSE & IT)
CS8591
OSI MODEL
● Open Systems Interconnection (OSI) model.
● International Organization for Standardization( ISO).
● OSI model is not a protocol; it is a model for understanding & designing a Network Architecture.
● OSI model is built of seven ordered layers.
● Each layer defines a family of functions different from other layer.

3. COMPUTER NETWORKS - (Common to CSE & IT)
CS8591
PHYSICAL LAYER
Functions of physical layer:
● Physical characteristics of interface & media
● Types of encoding
● Data rate
● Synchronization of bits
● Line configuration
● Transmission mode
● Topology

4. COMPUTER NETWORKS - (Common to CSE & IT)
CS8591
DATA LINK LAYER
Responsibilities:
● Framing – The segment of data in this layer is called
frames.
● Physical addressing – 48 bit address in the NIC
● Flow control – How the frames are going to be sent and
ack.
● Error control- The frames that are sent from source to
destination must be checked for errors.
● Access control – Which device accesses the Link.

5. COMPUTER NETWORKS - (Common to CSE & IT)
CS8591
NETWORK LAYER
Delivery of packets from the final source to the
original destination across multiple links(networks).
Responsibilities (Or) functions of Network layer:
● Logical addressing – Logical address is a 32 bit
address assigned to each system in a network(IP
address).
● Routing- The path through which the packets are
transmitted from source to destination.

6. COMPUTER NETWORKS - (Common to CSE & IT)
CS8591
TRANSPORT LAYER
Functions of Transport Layer:
● Service point Addressing
● Segmentation & Reassembly
● Connection Control
● Flow control
● Error control
Process to Process delivery of the entire message

7. COMPUTER NETWORKS - (Common to CSE & IT)
CS8591
SESSION LAYER
● Establishes, controls and ends the sessions between
local and remote applications.
● The services offered by the session layer are generally
implemented in application environments using remote
procedure calls (RPCs).
Functions:
Dialog Control : This layer allows two systems to start
communication with each other in half-duplex or
full-duplex.
Synchronization : This layer allows a process to add
checkpoints which are considered as synchronization
points into stream of data.

8. COMPUTER NETWORKS - (Common to CSE & IT)
CS8591
PRESENTATION LAYER
It is concerned with the syntax and semantics of the information
exchanged between two Systems.
Responsibilities:
Translation
● Sender dependant format into common network support
format.
● Common format into receiver dependant format.
Encryption/Decryption
● Security
● Encryption is the process of changing the plain text into
cipher text.
● Decryption is the process of changing the cipher text into
plain text.
Compression/Decompression
● Reduce the size of the data to be transmitted before
sending.
● Decompress the received data to the original size after
receiving.

9. COMPUTER NETWORKS - (Common to CSE & IT)
CS8591
APPLICATION LAYER
Some applications are:
● Network virtual terminal:
Network virtual terminal is a software version of a
physical terminal & allows a user to log on to a
remote host.
● File transfer,access and management
● Mail services- Email forwarding and storage
● Directory services – Access for global information
about various objects & services.
It provides user interfaces and support for services such
as email, remote file access,transfer and other types of
services.

10. COMPUTER NETWORKS - (Common to CSE & IT)
CS8591
Videos
1. https://www.youtube.com/watch?v=Ilk7UXzV_Qc
2. https://www.youtube.com/watch?v=-6Uoku-M6oY