THE OSI MODEL

The OSI [open system interconnection] is a worldwide federation that works to provide international standard. It is standard description or “reference model” for how massage should be transmitted between any two points in a telecommunication network. It is an OSI standard for worldwide communications that defines a network for implementing protocols in seven layers. The OSI model does provide important guidelines that are used by vendors, engineers, developers and services into different layers. Each layer has its own responsibilities and functioning.

                        The OSI model was meant to help vendors create inter operable network devices, so that different vender’s network could work with each other. The OSI has seven different layers divided into group. The top 3 group defines how the application within the end stations will communicate each other and with users.

                                                                        The bottom 4 layers define how data is transmitted end to end.

NO.      LAYER                                    FEATURES SERVICES

7          APPLICATION                        FILE, MESSAGE DATABASE APPLICATION

6          PRESENTATION                    DATA ENCRYPTION, COMPRESSION, TRANSLATION

5          SESSION                                 DIALOUGE CONTROL

4          TRANSPORT                          END TO END CONNECTION

3          NETWORK                             ROUTING

2          DATALINK                             FRAMING

1          PHYSICAL                               PHYSISAL TOPOLOGY

                        The each protocol at specific OSI layer communication with a protocols that operates at the same OSI layer on another computer (end). This happens through encapsulation.

            A message is constructed at the application layer and then passed down through the protocol stack. Each layer adds its own information to the message thus the message grows in size as it goes down the protocol stack. The message is then sent to the destination computer and the encapsulation is reversed by taking the message apart through the same step as the source computer that encapsulation it.

By :-Krishna kumar