While the OSI and TCP/IP layering models are available for reference, what is practically used in reality is a hybrid layering model, that leverages the best aspects of both these models. The Hybrid layering model is a 5 layer model as given in the diagram below:
In the Hybrid layering model
- All layers are similar to the TCP/IP layering model, except that the bottommost “Host-to-Network” layer of the TCP/IP model is replaced with the Datalink and Physical layer of the OSI layering model.
- The Application layer combines the functionalities of the top three layers of the OSI model, namely Application, Presentation and Session. This layer is primarily responsible for implementing different application layer protocols, along with their formating.
- The functionality of the Transport layer is same as the functionality of the Transport layer of the OSI and TCP/IP layering models. It takes care of end-to-end communication, multiplexing/demultiplexing data from different applications, flow-control, reliability and network congestion control.
- The Network layer of the Hybrid model primarily deals with end-to-end routing of packet data from the source computer to the destination computer.
- The data link layer is responsible for frame transmission, reception and error control.
- The physical layer is responsible for bit transmission through wired/wireless telecommunication links.