ISO-OSI Model

• ISO-OSI (International Standard Organization - Open System Interconnection)
• The ISO-OSI model is a seven layer architecture. It defines seven layers or levels in a complete communication system.
• OSI model defines a network framework to implement protocols in server layer.
• Control is passed from one layer to the next, starting at the application layer in one station and proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.

Application

↓

Presentation layer

↓

Session layer

↓

Transport Layer

↓

Network layer

↓

Data link layer

↓

Physical layer

Layer 1-Physical layer

The Physical layer of the OSI model is responsible for transmission of digital data bits from the Physical layer of the sending (source) device over network communications media to the Physical layer of the receiving (destination) device. It deal with communication media receives frame from data link layer and converted them in bits. It converts the digital/analog bits into electrical signal or optical signals. Data encoding is done.

Layer 2- Data link layer

Data link obtain data from physical layer and check for errors. Main function is defining the media access control or hardware address. Define how the network layer protocol is encapsulated in the data link layer frame. It provided both connection-less and connection-oriented services.

Layer 3-Network layer

Network layer provide logical address know as IP address .Router works on this layer. Main function define IP address.Find routes based on IP address to reach its destination. connect different data link type together like as token ring , serial, IDDI , Ethernet etc.