Protocol Layering

To provide structure to the design of network protocols, network designers organize protocols—and the network hardware and software that implement the protocols— in layers.

Layered Internet protocol stack

• Application Layer: supporting network applications
  • HTTP, IMAP, SMTP, DNS
• Transport Layer: process-process data transfer
  • TCP, UDP
• Network Layer: routing of datagrams from source to destination
  • IP, routing protocols
• Link Layer: data transfer between neighbouring network elements
  • Ethernet, 802.11 (wifi), PPP
• Physical Layer: bits “on the wire”