I have had an ongoing conversation with Marty Hollander at Vidyo about his company's claim that their video conferencing solution does not require QoS. Vidyo claims that the Scalable Video Coding (SVC) technology used by their products works so well in a lossy network that there is no longer a need to prioritize video conferencing traffic over other traffic types. I think rumors of the death of QoS are highly exaggerated.
SVC is a new video coding standard I have written about in previous postings. SVC does in fact work better than traditional codec technologies on networks that had some packet loss. This is a great advantage for networks that do not have QOS, especially the Internet. This is not the only advantage of SVC and I think this technology's advantages will make it a widely accepted encoding standard over the next few years.
But does that mean we no longer need QOS for video? I don't think so.
Video conferencing needs bandwidth. Video conferencing quality is directly related to the bandwidth available. High resolution images and high frame rates require more bandwidth than low resolution images and low frame rates. Users who normally experience high quality video such as HD 720p will be sorely disappointed with video quality if frame rates drop to 15 frames a second and/or resolution drops to CIF levels. A CIF/15fps connection may occur on a network exhibiting no packet loss, but because of the limited bandwidth, video quality is poor. If we want to have consistent high quality video, we have to ensure video gets the bandwidth it needs.
The IT team delivering video conferencing services within an enterprise must then manage the available bandwidth to ensure sufficient bandwidth is available to support the video conferencing requirements of the company. Insufficient bandwidth either means calls are denied or calls overload a network segment, causing packet loss and possibly causing endpoints to reduce the bandwidth at which they are transmitting. A drop in bandwidth demand may fix the packet loss situation but will cause video quality degradation just due to the lower-bandwidth communications path. To deliver consistent high quality video conferencing services, enterprise IT teams will need to design their networks to provide sufficient bandwidth for the expected video demand.
But applications have a way of demanding more and more of the network, so the network also needs to protect itself against an increasing tide of video usage. What is the best way to manage bandwidth in the network environment? Quality of Service.
One of the key values of QoS to the network team is that an application can be given a bandwidth allocation and forced to stay within that allocation when the network is congested. This capability is critical in any converged network environment because numerous different types of applications are equally important to the organization. Voice traffic, video conferencing traffic and the data applications that support the business must all be given appropriate bandwidth allocations to ensure they all deliver services that allow the enterprise workers to be productive.
If an enterprise uses SVC, can they downgrade video conferencing and not have it be the second-highest-priority traffic stream in the network? This might be attractive to enterprise network teams, especially if they have a mandate within the organization to support SAP, Documentum, Citrix, SaaS or other key data applications that drive the business on a daily basis.
I think this is still the wrong approach. Priority in the network should be assigned based on the needs of the application for low latency and low packet loss. Importance of an application with respect to business should be managed with appropriate bandwidth allocations. If the data application has a high priority to the business, ensure that its QoS class has sufficient bandwidth to guarantee the application can maintain the responsiveness needed during periods of heavy use and network load. Don't confuse QoS priority with importance to the business.
My view is that Even for video conferencing using the SVC technology. Bandwidth management is as important as priority in the design and management of applications in a converged network, and it comes through QoS.
