The OSI model of the TCP/IP stack has become the standard model for understanding how a packet flows into or out of a system. Here is my understanding.
7. Application Layer – User can interact. (GUI).
6. Presentation Layer – Encryption (SSL, SSH, IMAP, etc).
5. Sessions Layer – Manages sessions – (API’s, sockets).
4. Transport Layer – Assemble bits into packets. End to end. (TCP, UDP).
3. Network Layer – Transfers the data packets. (IP, ICMP).
2. Data Link Layer – Addressing & Physical Transmission. (Ethernet, switch, Bridge).
1. Physical Layer – Wires, hubs.