Open System Interconnect (OSI) is defined as the reference model used for network and troubleshooting. Computer manufacturers like IBM, Dell, Apple, HP, Acer.

An OSI model has seven layers namely:

*Physical layer.

*Data link layer.

*Network layer.

*Transport layer.

*Sessions layer.

*Presentation layer.

*Application layer.

Physical layer: It is the bottom most layer of an OSI model. It carries only binary digits like 0 and 1 and transfers them through cables. eg. ethernet and coaxial cables.Hubs and repeaters are the two networking devices that works in a physical layer. The data in the physical layer is known as BITS.

Data link layer: It is the second layer of an OSI model. This layer is used to identify the host network in other words the MAC or LLC address. Switch and Bridge are the two networking devices that works in a data link layer. In data link layer mainly used are LLC and MAC address. The data in data link layer is known as FRAMES.

Logical Link Control (LLC): it mainly does error detection.

Media Access Control (MAC): it mainly used to convert the data into binary form 0 and 1 and vice versa.

Network layer: It is the third layer of an OSI model. This layer is used to identify the destination network in other words the IP address. It also finds the best and efficient path of the delivery of data. Router is one of the networking devices that works in network layer. The data in the network layer is known as PACKETS.

Transport layer: It is the fourth layer of an OSI model. It is used as the best reliable delivery of data. The two protocols used in Transport layer are TCP and UDP. The datas in transport layer will be in the form of segments.

Transmission Control Protocol (TCP) is used for acknowledgement and reliable, error correction and hence slower than UDP.

User Datagram Protocol (UDP) is similar to ordinary layer which doesnot acknowledge, unreliability, no error correction and hence faster than TCP.

Session layer: It is the fifth layer of an OSI model. It is used for iniating, maintaining and terminating.

Presentation layer: It is the sixth layer of an OSI model. It is used for encoding and decoding and encryption and decryption of data. eg. jpeg, avi, mpeg. etc.

Application layer: It is the seventh layer of an OSI model. It is used as an end user interface. eg. http, pop3, smtp.