Question

Many real-time video applications run over UDP rather than TCP because they cannot tolerate retransmission delays. However, this means video applications are not constrained by TCP’s congestion-control algorithm. What impact does this have on TCP traffic? Be specific about the consequences

Answer 1

The use of UDP for real-time video applications can lead to increased network congestion, affecting TCP traffic by causing packet loss, extended RTTs, reduced throughput, and increased latency, resulting in overall degraded network performance.

Step-by-step explanation:

The usage of UDP for real-time video applications has a significant impact on TCP traffic, primarily due to the lack of congestion control in UDP. While UDP allows for continuous streaming without significant delay, it does not adjust its rate based on network conditions, unlike TCP's congestion-control algorithm. Therefore, when UDP traffic increases on a network, it can consume a large portion of the available bandwidth without scaling back during congestion, potentially leading to network congestion.

As a result, TCP traffic, which reacts to congestion by adjusting its transmission rate, may be indirectly affected. TCP flows might experience increased packet loss and extended round-trip times (RTTs) due to the reduced bandwidth and increased congestion caused by UDP traffic. This, in turn, can lead to reduced throughput and increased latency for TCP applications as they continually adjust their transmission window size in response to network conditions.

Moreover, the overall network performance can be degraded if the volume of UDP traffic is significant enough to continually trigger congestion responses from TCP traffic, essentially leading to a scenario where the TCP congestion-control algorithm is trying to stabilize a network that is being constantly destabilized by unregulated UDP traffic.

Answer 2

Video applications typically run over UDP rather than TCP because they cannot tolerate Re-transmission delays. However, this means video applications are not constrained by TCP’s congestion control algorithms.

(a). What impact does this have on TCP traffic? Be specific about the consequences.

Fortunately, these video applications often use RTP, which results in RTCP “receiver reports” being sent from the sink back to the source. These reports are sent periodically (e.g. once a second) and include the percentage of packets successfully received in the last reporting period.