OSI REFERENCE MODEL

OSI model:-

The model deals with connecting open systems i.e. systems open for communication with one another.

7 Layers of OSI model explained:-

A) The Physical Layer:-

1- It is concerned with transferring raw bits over a communication channel.

2- The design to be tackled here include, that when one side sends a 1 the other side also receives it as 1  bit, and not a 0 bit.

B) The Data Link Layer:-

1. The main task here is to transform a raw transmission facility into a line that appears free of undetected transmission errors to the network layer.

2. It accomplishes this by having the sender break in data into frames and transmit frames sequentially.

3. The receiver sends back the acknowledgement frame,after conferming receipt of each frame.

C)The Network Layer:-

1. It controls the operation of the subnet.

2. The key design issue here is determining how packets are routed from source to destination. It also controls the congestion problem to avoid collision between packets.

D)The Transport Layer:-

1. Basic function here is to accept data from above , split it up into smaller units , pass these to the network layer and ensure pieces all arrive correctly at the other end. The function thus should be performed efficiently.

2. It also determines what type of service to provide to the session layer and ultimately to the users if the network.

E) The Session Layer:-

1. It allows users on different machines to establish sessions between them.

2. Session offers various services including dialogue control, token management and synchronization.

F) The Presentation Layer:-

1. It is concerned with the syntax and semantics of the information transmitted.

2. It is used to define data structures, along with a standard encoding to be used on wire.

G) The Application Layer:-

1. It contains a variety of protocols that are commonly needed by users.

2. For ex. HTTP and other file transfer , electronic mail and network news protocols.

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