The OSI Model and TCP/IP Model

What is the OSI model?

The OSI model was the primary standard model for network communications, adopted by all major telecommunication companies and computers within the early 1980s. The users of a network are located across the world. So, an international group of standards has been developed for ensuring that nationwide and worldwide electronic communication systems may be developed and are compatible with one another. 

A conceptual framework has been developed by the International Organization of Standardization (ISO) in which these standards will fit. This framework is called Open System Interconnection (OSI) and it is generally referred to as the OSI reference model. The OSI model is a seven-layered architecture where each layer is assigned a specific task.

Functions of different layers

There are seven layers in the OSI model:

1. Physical layer 
2. Data-link layer
3. Network layer
4. Transport layer
5. Session layer
6. Presentation layer
7. Application layer

Their roles are as follows.

Layer 1: Physical layer

The lowest layer of the OSI reference model is the physical layer. The physical layer describes the electrical and physical specifications of the data connection. It contains information in the form of bits, and the digital data bits are converted into electrical signals. 

It defines the transmission mode, whether it is simplex, half-duplex or full-duplex between two devices on the network. The physical layer defines voltages and data rates needed for transmission. The physical layer isn’t concerned with protocols or other higher-layer items.

Layer 2: Data-link layer

The main function of a data-link layer is to handle the errors which might occur at the physical layer. The data-link layer is accountable for node-to-node delivery of the data. It takes packets from the network, breaks them into smaller pieces called frames and then passes them on to the physical layer. This layer adds a header to (Read more...)