3. Summary Table

Layer

Function

Examples

Application

User-facing services, data formatting, encryption

HTTP, HTTPS, FTP, SMTP, DNS

Transport

End-to-end reliability or fast delivery, flow control

TCP, UDP, port numbers (80, 443)

Internet

Routing, logical addressing

IP (IPv4, IPv6), ICMP, OSPF, routers

Link

Physical transmission, node-to-node transfer

Ethernet, Wi-Fi, ARP, switches, MAC addresses