Thursday, March 5, 2009

Scalable video conference servers

A lot of the discussion in the video industry these days is around video conference servers (also known as bridges and MCUs). With the advances of video communication technology and the deployment of HD video the load on video conference servers is growing because they have to process more bits per second to support HD video calls. In addition, desktop video deployments rapidly increase the size of video networks.

Fundamentally, there are three ways to make video conference servers more scalable. The first one is to build a large server, use carrier-grade architecture and try to squeeze in as much computing power as possible into a large chassis. This is the approach Tandberg is taking with the MSE 8000. The benefit of such approach is that it easy to explain to resellers, integrators and customers: ‘you had a small server, now you are running out of resources, so get a big one’. The disadvantage is that the server becomes an extremely critical single point of failure; if the server is down, or its part of the IP network is down, the entire video service is impacted. There is also the cost aspect - buying such large server is a considerable chunk of money – but I am looking at it from a network design perspective and can only say that it is impossible to find an optimum location for such server in the network. Enterprise, government, education and health networks are all so distributed these days that placing the server in any one location leads to inefficient use of the network bandwidth and decreased quality for participants from other locations.

The second approach to scalability is to build a conference server sufficient for mid-sized video deployments and create a new architecture that allows you to combine many such conference servers into one pool of conferencing resources – to meet the needs of large organizations. You can increase this pool by adding conference servers and decrease it by removing them. The management server that manages all resources reroutes video calls to the most appropriate resource in the entire network. You can make the selection algorithm as sophisticated as you want, e.g. the algorithm may select the conference server that is closest to the majority of participants, or select the server that has the horsepower to support the quality that the participants require for that particular call. The benefit of this architecture is that you can spread the conference servers across your networks – thus avoiding bottlenecks and congestions - and still manage all servers as one giant virtual conference server. This is Polycom’s architecture: the conference server is RMX 2000; the resource management server is DMA 7000. Networking experts understand the high reliability and survivability of this approach – distributed computing and load balancing have been the preferred way to achieve scalability of applications for long time. The real challenge with this approach is to educate traditional video equipment resellers and integrators who look at the conference server as ‘the bridge’ (i.e. one box) and not as a service that can and must be distributed across the network to scale.

The third approach is to completely change the distribution of computing power between endpoints and conference servers, i.e. move more of the computing to the video endpoints (requires more powerful/expensive hardware for endpoints) and reduce the computing power in the conference server. This is the approach which the startup Vidyo is taking. Simplifying the conference server is a great idea but it remains to be seen if this benefit can outweigh the need for more performance in the endpoints. More importantly, this approach is incompatible with the installed base of video equipment and requires signaling and media gateways for interoperability. Gateways – and especially media gateways – introduce delays, decrease video and audio quality, and add substantial cost to the solution.

You can find more details about the scalability mechanisms discussed in this posting, as well as diagrams explaining the configurations, in the white paper ‘Scalable Infrastructure for Distributed Video’ (see link in the ‘White Papers and Articles’ section below on this blog). I will also address this subject in my presentation ‘Visual Communication – Believe the hype and prepare for the impact’ at InfoComm (see link in the ‘Speaking Engagements’ section below).


  1. I gotta say videoconferencing is really useful hope you post more info regarding this.. Good luck!

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