Internet protocols

Protocols — rules to communicate over network

• TCPI/IP on ARPANET in 1982
• works locally (LAN) & on network
• various models of communication, mainly client/server, but also peer-to-peer and others.

IP (internet protocol):

• address in IPv4 is 32 bits
• associated with max 1 device at a time
• written as 4 dot-separated bytes
• transfers data packets from source to destination (like postal service)
• packets created by IP software contain:
  • header with source/destination address, length, etc.
  • data

TCP (transmission control protocol)

• provides guarantee that packet is delivered
• provides 2-way communication
• analogy: telephone status report
• adds ports (numbers) representing destination process on destination computer (with some being standard)
• higher-level protocols like SMTP, FTP, HTTP are built on top of this

UDP (user datagram protocol):

• like TCP
  • builds IP
  • provides ports
• unlike TCP
  • no connection concept
  • no transmission guarantee
• UDP is lightweight, better for one-time messages

DNS (domain name service)

• “phone book”
• maps IP to hostnames (www.example.org)
• top-level domain is the last part (.com, .org, . edu, etc.)

Analogy: IP is a telephone network, TCP is a conversation, UDP is a voicemail message, DNS is the yellow pages/directory assistance