A protocol consists of rules for specific messages sent and what specific actions to taken when a message is received/other events.

All communication activity in the Internet is governed by network protocols.

• protocols define the format, order, of messages send/received among network entities, and actions taken on message transmission and receipt

Recall the “protocols” view of the internet:

• protocols exist everywhere on the internet to control the sending/receiving of messages
  • e.g. HTTP (Web), streaming video, Skype, TCP, IP, WiFi, 4/5G, Ethernet
• Internet standards include:
  • RFC - Request for Comments
  • IETF - Internet Engineering Task Force

There is a layered internet protocol stack:

• Application
  • Supports network applications
  • e.g. HTTP, IMAP, SMTP, DNS
• Transport
  • Involves process-to-process data transfer
  • e.g. TCP, DNS
• Network
  • involves routing of datagrams from source to destination
  • e.g. IP, routing protocols
• Link
  • involves data transfer between neighboring network elements (e.g. routers)
  • e.g. Ethernet, 802.11 (WiFi), PPP
• Physical
  • involves bits “on the wire”

Packets are encapsulated - headers are added which tells us information about destination address, etc.

Packets are encapsulated layer-by-layer:

• Header of transport layer contains information about the process that should receive the packet