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The OSI Model has 7 layers : From top 1. Application 2. Presentation 3. Sessions 4. Transport 5. Network 6. Data Link 7. Physical . This is only a theoretical model and the de-facto standard is the TCP/IP Protocol suite which has only 4 layers. 1. Application, 2. Transport 3. Networking 4. Physical. The TCP is Transmission Control Protocol at the Transport Layer and IP is Internet Protocol at the Networking layer. And they are almost always used for any communication. Hence the whole suite itself is called the TCP/IP Suite of Protocols.