UDP

Concept

User Datagram Protocol(UDP)

• connectionless, single datagram socket handles all traffic
• no reliability
• no congestion control
• small header (8 bytes)
• fast

 0      7 8     15 16    23 24    31  
+--------+--------+--------+--------+ 
|     Source      |   Destination   | 
|      Port       |      Port       | 
+--------+--------+--------+--------+ 
|                 |                 | 
|     Length      |    Checksum     | 
+--------+--------+--------+--------+ 
|                                     
|          data octets ...            
+---------------- ...

UDP Checksum

• wrap around carry -> 1s complement(flip all bits) == checksum
• detect single bit flips
• compute checksum over the packet(in 16-bit chunks), check if checksum values match
• sender: computes with checksum = 0 initially -> insert computed checksum into packet
• receiver: computes checksum -> should find that checksum == 0