7 - Application: end-user protocols (HTTP, SMTP, DNS, FTP) 6 - Presentation: data formatting, encryption (SSL/TLS) 5 - Session: establish/manage/terminate sessions 4 - Transport: end-to-end delivery, error correction (TCP, UDP) 3 - Network: logical addressing, routing (IP, OSPF, BGP) 2 - Data Link: MAC addressing, framing (Ethernet, Wi-Fi) 1 - Physical: bits, cables, connectors Mnemonic: "All People Seem To Need Data Processing"