OSI Model in Computer Network
OSI (Open Systems Interconnection) is a networking architecture that operates on 7 layers. Each layer has its characteristics and capabilities which when combined, allow for the transmission of data all over the world.
The 7 layers include :
Physical Layer
It is the bottom-most layer and deals with the transmission of raw bits of data. It transmits data across the network from the sender’s to the receiver’s physical layer.
Functions :
- Data Transmission : Decides among simplex, half-duplex or full-duplex transmission modes between the devices.
- Topology : Overlooks the arrangement of network devices.
- Signals : Decides which type of signal should be used for transmission.
- Bit rate control & Bit Synchronization : Controls the transmission rate of bits and provides synchronization.
Data Link Layer (DLL)
It looks after the error-free transfer of data among nodes. Also, it structures the format of data on the network.
Data Link Layer consists of two sub-layers :
- Logical Link Control Layer
- Media Access Control Layer
Functions :
- Framing : Translation of raw bits into packets called ‘frames’. Also designates distinguished patterns to the frames for meaningful transmission of information.
- Physical Addresses : Gives physical addresses of sender and receiver in each frame.
- Error and Access Control
Network Layer
This layer is responsible for routing, device addressing, location tracking of devices on the network and data transmission from one host to another in different networks.
Functions :
- Internetworking : Sets up a logical connection among various devices of the network.
- Addressing : Embeds source and destination addresses to the frames which help in the identification of devices.
- Routing : Chooses the most optimum path for transmission.
Transport Layer
It manages the order of transmission and makes sure there is no duplication. It also looks after the complete transmission of data from the sender to the receiver.
Functions :
- Segmentation and Reassembly : It breaks down information into smaller bits while sending data and reassembles them while receiving.
- Service Point Addressing : Specifies a specific type of address, called the “Service Point Address” or port address, in the layer header, so that the information is delivered to the correct process.
Session Layer
It handles the interaction between devices and establishes connections. It also maintains security and synchronizes sessions.
Functions :
- Synchronization : Adds checkpoints while sequentially transmitting data to improve error identification.
- Dialog Control : Provides and controls a dialog between two systems for mutual communication.
Presentation Layer
It is also referred to as the Translation Layer. It is responsible for the syntax and semantics of data transmission.
Functions :
- Translation : Transforms data from a sender-dependant format to a common format and then to a receiver-dependant format.
- Encryption : Translates data into a secure format to maintain privacy during transmission.
- Compression : Reduces the overall size of data transmitted by reducing the number of bits without losing the originality of the information.
Application Layer
The top-most layer of the OSI model, Application Layer acts as a window to the network services and allows access to users and applications.
Functions :
- File transfer access and management (FTAM) : Facilitates remote access and management to systems in the network.
- Mail Services
- Directory Services
OSI Model in Computer Network