UDP (User Datagram Protocol)


UDP Protocol

UDP Protocol (User Datagram Protocol) is another Tranport Layer Protocol. It is simpler than TCP. We will also see the differences of these two protocols in TCP vs UDP lesson. It is generally used in unsenstive communications and real time applications that do not need a secure data transmission mechanims. For example live video conference, voice traffiv and gaming applications are the services in which UDP Protocol is used.


UDP is a Connectionless Protocol. There is no need to establish a session to use UDP. For TCP, as we have talked about before, a session must be established with Three-Way Handshake.


UDP is not a Reliable protocol. UDP do not care about if the data is received or not. Generally applications that provide its own Error-recovery, use UDP. This make UDP, a Best Effort (fast) protocol. So, generally UDP used for real time applications, that need fast and efficient transmission such as voice calls, video calls, games etc.


UDP is susceptible to the data loses, duplicate traffic and non-orderly delivery. It only concentrate on Best-Effort (Fast) transmission.


There is no Ordering Mechanism in UDP. If any order is required, the Application Layer do this for that traffic.


For the realtime services like computer gaming, voice or video communication, live conferences; we need UDP. Since high performance is needed, UDP permits packets to be dropped instead of processing delayed packets. There is no error checking in UDP, so it also save bandwidth.


Wellknown UDP Ports


Some network services uses different transport layer protocols and their ports. The network services that uses UDP Ports and their Port Values are given below:

• DNS (Port 53)
• DHCP (Port 67)
• TFTP (Port 69)
• SNMP (Port 161)
• SNMP Trap (Port 162)
• RIP (Port 520)



UDP Header


UDP Protocol Header has a fixed ans simple header. The total length of UDP Protocol Header is 8 Bytes. This length is variable for TCP. A TCP header  length can be a value between 20 and 60 Bytes.


So, what are the fields of this UDP Header? There are :


  • 16 bits Source Port,
  • 16 bits Destination Port,
  • 16 bits Length field
  • 16 bits Checksum field.


The Port numbers can be a value between 0 and 65535.  And the length is the total length of the UDP Header and the Data part.




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