Layered Models: OSI and TCP/IP

• OSI Model (7 layers, top to bottom): Application → Presentation → Session → Transport → Network → Data Link → Physical (mnemonic: "All People Seem To Need Data Processing")
• TCP/IP Model (4 layers): Application → Transport → Internet → Network Access/Link — the practical model the real Internet is built on; maps roughly onto OSI but combines several OSI layers
• OSI is more of a theoretical/reference model; TCP/IP is the practically implemented model

MCQ Trap

• OSI has 7 layers; TCP/IP has 4 layers — know the mapping, especially that TCP/IP's Application layer covers OSI's Application + Presentation + Session layers.