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The TCP IP model is a model with four layers, which is for both modeling current internet architecture

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as well as providing a set of rules that govern all forms of transmission over a network.

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DARPA, an agency of the United States Department of Defense, created it in the 1970s.

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This model was being made at the same time the OSI model was created.

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The TCP IP model is not the same as the OSI model.

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However, it was influenced by the model, which is why many of the names of the different layers are

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the same.

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So we can simply say that the TCP IP reference model represents reality in the real world, whereas

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the OSI reference model represents an ideal.

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Okay.

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So these are the main differences of the TCP IP reference model.

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The three top layers in the OSI model, that is the application layer.

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The presentation layer and the session layer are not distinguished separately in the TCP IP model,

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which only has an application layer above the transport layer.

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TCP corresponds to OSI layer four, the transport layer.

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IP corresponds to a subset of OSI layer three, the network layer.

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TCP IP makes no prescriptions as to the link layers below IP, while OSI specifies two layers.

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The physical address commonly the Mac address, which is located in a special field in the data link

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layer header changes as the packet passes from one device to another.

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For example, from the source PC to a switch to a router to another switch, and then finally to the

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destination PC.

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However, the original IP source and destination addresses do not change when transiting the network

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because the packet is stripped of its layer three header only when it goes beyond a router.

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When it stays within the same LAN, it only passes through switches which decapsulation it at the layer

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two header containing the Mac address.

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As a result, the header changes as the packet is re encapsulated, as does the Mac address fields.