How do OSI model layers map to TCP/IP layers?

• A. Application (Application, Presentation, Session) maps to TCP/IP Application; Transport maps to TCP/IP Transport; Internet maps to TCP/IP Network; Link maps to TCP/IP Data Link and Physical
• B. Application (Application, Presentation, Session) maps to TCP/IP Application; Transport maps to TCP/IP Transport; Internet maps to TCP/IP Network; Link maps to TCP/IP Data Link and Physical
• C. All OSI layers map one-to-one to TCP/IP as Application, Transport, Internet, Link
• D. The OSI model has no relation to TCP/IP

Answer: (B)

The main idea is that TCP/IP and OSI organize networking into different numbers of layers, so the mapping combines several OSI layers into a single TCP/IP layer. The OSI upper layers—Application, Presentation, and Session—all serve application-level communication and data handling, so they fit together under the TCP/IP Application layer. The OSI Transport layer lines up with the TCP/IP Transport layer, handling end-to-end delivery. The OSI Internet layer corresponds to the TCP/IP Internet (or Network) layer, which is about routing packets between networks. Finally, the OSI Link and Physical layers cover the details of the actual data transmission media, which map to TCP/IP Data Link and Physical layers. So the best mapping is that the OSI top three layers merge into TCP/IP Application, the Transport layer stays as TCP/IP Transport, the Internet layer maps to TCP/IP Network, and the Link/Physical layers map to TCP/IP Data Link and Physical.