- 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.
- 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.