User Datagram Protocol(用户数据报协议)

Feature

• RFC 768
• best effort
  • out of order
  • lost packet
• simple
  • no connection establishment
  • no states
  • smaller segment header
  • no congestion control

header

8 bytes

16bit	16bit
source port	dest port
length	checksum

• length: in bytes of UDP segment, including header
• checksum

  detect "errors"(e.g. flipped bits) in transmitted segment

  • RFC 1071
  • sender
    • treat segment contents as a sequence of 16-bit integer
    • checksum: addition(1's complement of the sum) of segment contents(16-bit words)
    • sender puts checksum value into UDP checksum field
  • receiver
    • compute the checksum of received segment
    • check if computed checksum equals checksum field value
      • true: no error detected. Pass.(no error nonetheless?)
      • false: error detected

Used by

• Application Protocol
  • DNS
  • SNMP
• Streaming multimedia
• RDT at application layer