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UDP : User Datagram Protocol

UDP : User Datagram Protocol. Computer Network System Sirak Kaewjamnong. UDP : User Datagram Protocol. RFC 768 connectionless protocol (no connection establishment) provide unreliable service use socket as TCP. UDP Encapsulation. With Ethernet frame protocol type in IP header = 17.

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UDP : User Datagram Protocol

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  1. UDP : User Datagram Protocol Computer Network System Sirak Kaewjamnong

  2. UDP : User Datagram Protocol • RFC 768 • connectionless protocol (no connection establishment) • provide unreliable service • use socket as TCP

  3. UDP Encapsulation • With Ethernet frame protocol type in IP header = 17 UDP datagram Ethernet header IP header UDP header data

  4. Ports • Port : A 16 bits address allocated for the most common application level service • UDP and TCP use port addressing to deliver information to applications • Service are known by port number • FTP 20, TELNET 23, SMTP 25, HTTP 80

  5. Ports • Port numbers are generally allocated by • 0 not used • 1- 255 Reserves port to well known service • 256 - 1023 Other reserve port • 1024 - 65535 user defined server ports • UNIX store general used ports in /etc/service

  6. Sockets Port number • Socket : a pair of the IP address and the port number 172.28.80.96, 5160 • IP address is a unique to a node, the port is unique on a node the socket gives a unique identification of an application layer service IP address

  7. Socket Address • A connections identified by the socket address at its to ends • client socket : 172.28.80.96,3000; 192.168.100.3 ,21 • server socket : 192.168.100.3,21 ; 172.28.80.96,3000 IP 172.28.80.96 IP 192.168.100.3 connection Client port: 3000 Server port: 21

  8. UDP Format 15 16 0 31 Source port :16 Destination port: 16 • Source and destination port : 16, 16 identify applications at ends of the connection • length: 16 - length of datagram including header and data • checksum :16 -one’s complement of header and data including pseudo data UDP length :16 Checksum : 16 data

  9. Source IP address : 32 Destination IP address : 32 Pseudo header Zero:8 Protocol : 8 UDP length :16 Source port : 16 Destination port : 16 UDP header UDP length : 16 Checksum : 16 Data…. UDP Pseudo Header 0 7 8 15 16 31

  10. UDP Pseudo Header • Include destination for double checking that destination is correct • if datagrams be an odd number of bytes, UDP append a pad byte of 0, just for computation • 0 indicates no checksum (checksum disable) • if compute checksum is 0, it stores as all one bits (65,535)

  11. UDP for Application • TFTP • DNS • RPC, NFS • SNMP

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