XCCC: Bandwidth Considerations for Conferencing over the Internet (290174)

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One of the advantages of IP Multicasting is bandwidth efficiency. However, because Internet clients need to participate in conferences by using the H.323 protocol, bandwidth is a major consideration for many customers. When you enable H.323 fallback, the audio codec used is G.711, which consumes roughly 70 kilobits per second (Kbps), while the video codec used is H.263, which consumes approximately 90 Kbps. Therefore, clients that are connecting to a conference will send an average of approximately 160 Kbps for each audio/video stream. This means that for every connection, you need approximately 160 times the amount of conference participants that are actively sending voice and video for a smooth conference. However, because of the inherent nature of the Internet, that is, congestion, dropped packets, collisions, and so on, this amount of bandwidth does not guarantee that there will not be any problems.

Determining the required bandwidth for data conferencing is difficult because of the many variables involved, such as whether or not you will be chatting, using a white board, or sharing applications. In any event, compared to the bandwidth that is consumed by audio and video, data conferencing uses relatively little resources.

The following is an analysis of the various connectivity methods and how the resulting bandwidth affects audio and video performance.

Methods for Controlling Bandwidth Usage

An administrator has several options for controlling the amount of bandwidth that is used in a conference. This section lists each of these methods.

• Selecting the codecs to be used. The codec of the resource that is used when the conference is scheduled defines the characteristics of the conference. For example, if you use G.711, each audio stream uses approximately 70 Kbps, whereas using GMS 6.10 reduces this to about 20 to 30 Kbps. For video, both H.261 and H.263 use approximately 90 Kbps. However, the H.263 codec has a smarter algorithm and uses slightly less network bandwidth.
• Reducing the Maximum number of conference participants setting for video resource.
• Defining audio-only resources.
• Setting default settings for audio/video to not send at join time.
• Implementing Quality of Service (QoS) policies. Microsoft Windows 2000 QoS includes enterprise and subnet policies that contain rules for your enterprise. You can set QoS policies to guarantee the amount of available bandwidth to your organization, subnets, or individual users.
• Limiting videoconferences over WAN links with administrative scoping.
• Restricting the use of expensive resources.

For additional information about bandwidth considerations and methods, please see the Concepts and Planning documents in the Documents folder on the Exchange Conferencing Server CD.