1. The document describes how data is transmitted between two computers, A and B, using the OSI model. 2. It explains that computer A packages the message with headers at each layer of the OSI model before transmitting it to computer B. 3. Computer B then unpacks the data layer by layer to retrieve the original message and pass it to the appropriate processes.

1. 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.

3. 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.

4. 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.