Introduction of ISO Layer

Open System Interconnection (OSI) Model

The Open System Interconnection (OSI) model is based on a proposal by the International Standardization Organization (ISO) as the first step toward international standardization of the protocols used in the various layers. This model is called the ISO-OSI Reference Model because it deals with connecting open systems -that is, systems that are open for communication with other systems. The OSI model has seven layers:

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

Application Layer : 

This layer supports semantic exchanges between applications existing in open systems. This layer also provides access to the lower IOS functions and services. This layer deals with the application software.

Presentation Layer :

This layer concerns itself with the representation of the data to the end user or application. This includes data conversion and code translation.

Session Layer : 

This Layer provides the mechanism for organizing and structuring interaction between applications and/or devices. It also provides synchronization.

Transport Layer : 

This layer is responsible for transparent and reliable transfer of data. It accepts data from the session layer, splits it into smaller units if need be, and passes these to the network layer. It provides flow control and error control.

Network Layer : 

This layer is the agent for establishing connection between networks. The standard also includes operational control procedures for inter-network communications as well as routing information through multiple networks.

Data Link Layer : 

This layer provides the functions and protocols to transfer data between network resources and to detect errors that may occur in the physical layer. It provides flow control, error control, framing etc.

Physical Layer : 

This layer defines the mechanical, electrical, functional and procedural standards for the physical transmission of data over the communications medium.