Osi(4)

Example of Data Transmission In OSI Model

Let us assume that a process at computer A (sending node) wants to send a message M to a process at computer B (receiving node).

1. The sending node's process builds the message M and passes it to the application layer on its machine. The application layer software adds a header (H7) to M and passes

the resulting message to the presentation layer as shown in fig.

2. The information added by each layer is in the form of headers or trailers. Headers are added to the message at the layers 6, 5, 4, 3, and 2. A trailer is added at layer 2.

3. At layer 1 the entire package is converted to a form that can be transferred to the receiving machine. At the receiving machine, the message is unwrapped layer by layer with each process receiving and removing the data meant for it.

Advantages of OSI Model are:

1.  The OSI models clearly defines services, interlaces and protocols. It defines that which services are provided by which layer, how the processes situated above a particular layer will

access its functionality and how a layer would use its protocols to do its job.

2.   The protocols of ISO model are better hidden and can be replaced with other suitable protocols easily.

3.  It is truly a general model.

4. It supports connection oriented as well as connectionless services.

Disadvantages of OSI model are

1. Sessions and presentation layers are not of much use.

2. The OSI model was built first and then protocols were designed to fit the need of network architecture. So in real life there is a problem of fitting protocol into the model.