LAYERS OF OSI MODEL

PHYSICAL LAYER

1) Physical layer is the lowest layer of the OSI model. This layer transmits raw bits over a communication channel. The design issue of physical layer considers four factors. They are electrical, mechanical, procedural attributes and functional attributes. The electrical attributes describe the voltage level or current level. The mechanical attributes describe the connectors and the wires of the interface. The functional attributes describe the function to be performed by the physical interface and the procedural attributes describe what connectors must do and the sequence of events required to effect data transfer across the interface.

DATA LINK LAYER

2) The data link layer is responsible for the transfer of data over the channel. It groups zeros and ones into frames. A frame is a series of bits that forms a unit of data.DLL detects and corrects the transmission errors using error correction method. It also provides data flow control to ensure that the DTE does
not become overburdened. It identifies the devices on the network.

NETWORK LAYER

3) The network layer specifies the intra-network operations and different types of addressing and rooting services. Logical and service addressing are provided from network layer. It also provides switching control and terminal connections. The X.25 specification is included in this layer.

TRANSPORT LAYER

4) The transport layer is responsible for reliable end to end data transfer. Hence optimum utilization of network resources. The transport layer performs the service of sequence numbering and message acknowledgement.

SESSION LAYER

5) The session layer adds mechanisms to establish, maintain, synchronize and manage communication between network entities. This layer has specific services, primitives, and protocol data unit which are defined in ISO.

PRESENTATION LAYER

6) The presentation layer is responsible for data compression, data expansion, data encryption and data decryption. It accepts data type i.e. int. char etc. from application layer and then negotiate with its peer layer as to the syntax
representation.

APPLICATION LAYER

7) The application layer supports end user functions like LOGIN, password file transfer. This layer contains service elements to support application process such as job management, financial data exchange and business data exchange. This layer also supports virtual terminal and virtual file concept.