Microsoft KB Archive/290174

= XCCC: Bandwidth Considerations for Conferencing over the Internet =

Article ID: 290174

Article Last Modified on 10/28/2006

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APPLIES TO


 * Microsoft Exchange 2000 Conferencing Server

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This article was previously published under Q290174





SUMMARY
This article discusses bandwidth requirements that an administrator may need to consider when configuring Exchange 2000 Conferencing Server for Internet access.



MORE INFORMATION
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.

Modem: 14.4 Kbps to 33.6 Kbps

Scenarios Supported: None.

Results: Jittery sound; dropped packets.

Workaround/Fix: Upgrade hardware and bandwidth.

Modem: 56 Kbps

Scenarios Supported: None (it may work fine with audio only between two people but this is not recommended).

Results: Jittery sound; dropped packets.

Workaround/Fix: Upgrade bandwidth or use point-to-point connectivity with NetMeeting instead of Exchange Conferencing Server (NetMeeting has a dynamic jitter control algorithm that scales better in low-bandwidth scenarios).

ISDN: 64 Kbps

Scenarios Supported: Audio with very little data sharing (no video, either sending and receiving).

Results: Intermittent and choppy audio may occur.

Workaround/Fix: Verify that the appropriate bandwidth setting is selected in NetMeeting (as always, an upgrade of bandwidth will increase performance).

ISDN: 128 Kbps

Scenarios Supported: Audio with very little video and data sharing.

Results: Slight jittery or choppy audio and delays in the video frames.

Workaround/Fix: Verify that the appropriate bandwidth setting is selected in NetMeeting (as always, an upgrade of bandwidth will increase performance).

DSL or Cable Modem

Scenarios Supported: Audio with very little video and data sharing.

Results: Same as ISDN with respect to the bandwidth.

Workaround/Fix: Verify that the appropriate bandwidth setting is selected in NetMeeting (as always, an upgrade of bandwidth will increase 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.

Keywords: kbinfo KB290174

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