The TCP IP model is a model with four layers, which is for both modeling current internet architecture
as well as providing a set of rules that govern all forms of transmission over a network.
DARPA, an agency of the United States Department of Defense, created it in the 1970s.
This model was being made at the same time the OSI model was created.
The TCP IP model is not the same as the OSI model.
However, it was influenced by the model, which is why many of the names of the different layers are
the same.
So we can simply say that the TCP IP reference model represents reality in the real world, whereas
the OSI reference model represents an ideal.
Okay.
So these are the main differences of the TCP IP reference model.
The three top layers in the OSI model, that is the application layer.
The presentation layer and the session layer are not distinguished separately in the TCP IP model,
which only has an application layer above the transport layer.
TCP corresponds to OSI layer four, the transport layer.
IP corresponds to a subset of OSI layer three, the network layer.
TCP IP makes no prescriptions as to the link layers below IP, while OSI specifies two layers.
The physical address commonly the Mac address, which is located in a special field in the data link
layer header changes as the packet passes from one device to another.
For example, from the source PC to a switch to a router to another switch, and then finally to the
destination PC.
However, the original IP source and destination addresses do not change when transiting the network
because the packet is stripped of its layer three header only when it goes beyond a router.
When it stays within the same LAN, it only passes through switches which decapsulation it at the layer
two header containing the Mac address.
As a result, the header changes as the packet is re encapsulated, as does the Mac address fields.