CCIE 400-101: Network Principles - UDP Operations


  • When TCP flows are combined with UDP flows within a single traffic class and the class experiences congestion, TCP flows continually lower their transmission rates (global synchronization), potentially giving up their bandwidth to UDP flows that are oblivious to drops.
  • This effect is called TCP starvation/UDP dominance.
  • The best way to resolve this is to classify UDP and TCP streams separately as much as possible.


  • Latency is the end to end delay.  
  • Jitter is the variance in latency. 
  • UDP is connectionless, the real effect of the latency on the UDP stream is that there would be a great delay between the sender and the receiver.  
  • Jitter causes problems with UDP streams if packets arrive in the wrong order.  
  • Jiffer can be smoothed by buffering.

RTP/RTCP concepts

  • UDP is the preferred protocol for real-time data transport like voice and video. 
  • However, UDP does not have any data flow management mechanisms like datagram sequencing or other "missing pieces". 
  • These functions are handled by RTP instead. 
  • For example, to help guarantee that datagrams are played back in the right order, RTP has a 16-bit sequence number field in its packet header, which allows the receiving device to ensure that the packets are correctly sequenced. 
  • Simply put, RTP carries the actual data, such as voice or video. RTCP carries information about that data – information such as jitter and delay statistics, or information about QoS mechanisms involved with these conversations.


UDP Operations