Video conferencing is a real-time communications technology, like VoIP, which requires special treatment on the IP network. The wide area network (WAN) is a critical component of the infrastructure supporting video conferencing
The critical requirements of the WAN video conferencing network design are as follows:
- To ensure that the WAN has adequate bandwidth.
- To properly classify traffic and support that traffic in a dedicated class.
- To support call admission control for bandwidth management.
- To properly locate the multipoint conferencing unit or bridge.
- To measure and monitor the WAN vendor.
Let's take a look at each of these requirements in turn.
- Determining adequate bandwidth for WAN video conferencing
Video conferencing sessions can consume significant amounts of bandwidth. Video conferencing can operate with as little as 400 Kbps of network traffic but may operate as high as 4 Mbps or even 6 Mbps of network traffic per call. The network designer must first determine the bandwidth of each video call by comparing the different resolution and frame rates available and determining which settings are best for the business application. The network designer must then determine the number of concurrent calls from each WAN-connected location. The call rate multiplied by the number of concurrent calls will determine the bandwidth requirement on each network access link. Remember to add IP overhead. Traditional video conferencing bandwidths are given as the transport bandwidth (e.g., 512 Kbps) where what the network actually experiences is about 20% higher (e.g., 615 Kbps). This is because video conferencing bandwidth values date from the days when it was all being carried on IDSN, which does not have any overhead. Signaling is out of band, but in an IP network we need overhead to create the packet headers that get the data from one computer to the next. This 20% is the overhead of the wrappers that let the IP network know how to handle the data (addressing, timing, protocol encapsulation, etc.).
- WAN traffic classification
The voice and video streams from a video conferencing endpoint must be given priority treatment in the network (overlay and converged) to maintain audio and video quality. A network class should be dedicated to video, and this class should be of a higher priority than all other application traffic except VoIP. The correct marking for this class will be provided by the WAN vendor. This marking should be put on the IP packets by the endpoint itself through proper configuration of the video endpoint. The network should be designed to trust the endpoint based on its IP address, subnet or port range.
- Video conferencing CAC
Once the bandwidths for the network have been calculated and put in place, the video conferencing application must stay within the design constraints. As additional systems are deployed, it becomes possible for video to overdrive the network, which will create packet loss and thus poor-quality video. The video conferencing infrastructure must have a call admission control (CAC) mechanism in place so that when the bandwidth for a specific network link is fully utilized, subsequent call requests which use that link will be denied.
- Locating the WAN video conferencing bridge
The video conferencing bridge is a bandwidth hotspot because all video conferencing calls participating in multipoint conferences must directly connect to the bridge. Thus, the bandwidth demand of the bridge connection can be significant. The best location for the bridge is in a collocation facility directly connected to the WAN core. This location provides inexpensive high-bandwidth connectivity and ensures that the design will scale as additional video conferencing endpoints are added to the enterprise.
- Trust and verify WAN video conferencing QoS
Network monitoring is a critical component of maintaining a high-quality video conferencing service. A path-based measurement tool should be used to measure the behavior of the network. The statistics gathered by traditional data network tools are not sufficient for monitoring the behavior of networks for voice and video conferencing. The voice and video monitoring tool should be an operational tool that collects information on a 24/7 basis and stores this information in a database. The tool will allow forensic analysis, trending, triggers based on thresholds, and real-time views of the behavior of the network in support of video conferencing. Currently, no video vendors have this kind of tool, but other vendors sell video network management tools.
- WAN video conferencing network design takeaways
These critical steps are all needed to ensure consistent, high-quality video service delivery across the WAN. Work with your WAN vendor to ensure that it has the right capabilities and that your network design meshes with the WAN service provided. Spending the time to get a good scalable design in place will pay off as video conferencing becomes an integral communications tool for the enterprise.
- About the author:
John Bartlett is a principal consultant at NetForecast, where he focuses on network support for voice and video conferencing. NetForecast provides consulting to enterprises and networking equipment vendors on application performance issues and convergence of voice and video conferencing on the IP network. John has 32 years of experience in the semiconductor, computer and telecommunications fields in marketing, sales, engineering, manufacturing and consulting roles. He has contributed to microprocessor, computer and network equipment design for over 40 products and has been consulting since 1996. John can be reached at firstname.lastname@example.org.
This was first published in February 2010