The OSI model is a 7-layer framework established in 1984 by ISO for designing network systems. Each of the seven layers defines the process of moving information across a network, from the physical layer dealing with physical connectivity to the application layer interacting directly with software applications. The layers include physical, data link, network, transport, session, presentation, and application layers, with the lower layers providing services to higher layers and handling physical and data link functions.

1. THE OSI MODEL
Open Systems Interconnection model
Established in 1947,
by the International Standards Organization (ISO)
It is layered framework for the design of network systems
It consists of seven separate but related layers
Each Layer defines the process of moving information
across a network

2. Layers of OSI Model
Application
7
Presentation
6
Session
5
Transport
4
Network
3
Data Link
2
Physical
1

3. Each layer in the a stream of bits to device B (through intermediate it receives
Device A sends sending device adds its own information to the message nodes). from the
Within a above it and passes the wholecalls upon the layer just below it.
layer just single machine, each layer package to the services of the layer just below it.
A
Application
Message
Application
Message
Presentation
Session
Presentation
Message
Session
Message
Transport
Network
Transmission
Media
Message
Data Link
Network
Data Link
Physical
B
Message
01100100
Physical
Message
Message
Message
Message
C
Transport
Network
Data Link
Physical

4. Classification of Layers
Application
Presentation
Session
Transport
Network
Data Link
Physical
7
6
5
4
3
2
1
The Network Support Layers
These Layers dealt with the physical
The transport can befrom the two as
These layers layer, thought of
aspects of moving data links one device
subgroups and ensures that what
the user support
to another such as- layers; they allow
the lower layers have transmitted
interoperability among unrelated
Electrical
is in a form•that the specifications
software systems upper layers
can use. • Physical connections
• Physical addressing
• Transport timing
• Reliability).
Transport Layer
User Support Layers

5. 7
Application
6
Presentation
5
Session
4
Transport
3
Network
2
Data Link
1
Physical
Software
Hardware + Software
Hardware only