Maintaining user Quality of Experience (QoE) is immensely challenging for video applications because it is difficult to measure success in delivering high-quality video. Video applications do not have a widely accepted video quality standard equivalent to the MOS for audio. Video quality is more subjective than audio quality, and it is more complicated to implement.
Video is finicky. Like VoIP, it has stringent performance requirements. Its real-time, streaming behavior resembles VoIP, but some of the performance metrics that affect VoIP call quality have a more powerful effect on video. For example, packet loss causes a syllable or two to drop out of a call. For a viewer of a video, packet loss causes pixelation and probably slow or frozen images. Jitter on a call makes the audio sound scratchy or garbled. Jitter during a video conference both distorts the image and scrambles the speech. The effects are both more noticeable and more annoying. Video requires a network that is expertly tuned, adequately or even over-provisioned, and carefully monitored.
Video applications have a much greater throughput requirement than VoIP. Video packets are large to begin with, and a key point to remember is that a video conference also has an audio component. One video stream takes from 300 to 400 kbps in each direction. Add the audio, and you have more than 800 kbps for combined video and audio streams.
On the LAN, video performs well. However, a desktop video deployment means that some video streams are sent point-to-point, between a pair of users. Others are multicast, for a video conference or webcast, for example. A slow link or busy interface presents a potential issue for these users. Using desktop video conferencing enables cross-site collaboration, which usually means video calls must travel across WAN links to reach remote offices. When they compete for bandwidth with other application traffic, these data streams can create bottlenecks on WAN links and WAN-LAN interfaces.
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