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Media Traffic Network Usage

Lync Server 2010
 

Topic Last Modified: 2010-11-17

The media traffic bandwidth usage can be challenging to calculate because of the number of different variables, such as codec usage, resolution, and activity levels. The bandwidth usage is a function of the codec used and the activity of the stream, both of which vary between scenarios. The following table lists the audio codecs commonly used in Microsoft Lync Server 2010 communications software scenarios.

Audio Codec Bandwidth

Audio codec Scenarios Audio payload bitrate (KBPS) Bandwidth audio payload and IP header only (Kbps) Bandwidth audio payload, IP header, UDP, RTP and SRTP (Kbps) Bandwidth audio payload, IP header, UDP, RTP, SRTP and forward error correction (Kbps)

RTAudio Wideband

Peer-to-peer

29.0

45.0

57.0

86.0

RTAudio Narrowband

Peer-to-peer, PSTN

11.8

27.8

39.8

51.6

G.722

Conferencing

64.0

80.0

95.6

159.6

G.711

PSTN

64.0

80.0

92.0

156.0

Siren

Conferencing

16.0

32.0

47.6

63.6

The bandwidth numbers in the previous table are based on 20ms packetization (50 packets per second) and for Siren and G.722 include the additional secure real-time transport protocol (SRTP) overhead from conferencing scenarios and assume the stream is 100% active. Forward Error Correction (FEC) is dynamically used when there is packet loss on the link to help maintain the quality of the audio stream.

For video, the codec is always RTVideo.The bandwidth required depends on the resolution, quality, and frame rate. For each resolution, there are two interesting bit rates:

  • Maximum payload bitrate   This is the bitrate that a Lync 2010 endpoint will use for resolution at the maximum frame rate supported for this resolution. This value is interesting because it allows the highest quality and frame rate video.
  • Minimum payload bitrate   This is the bitrate that a Lync 2010 endpoint will use for a resolution of approximately 1 frame per second. This value is interesting so that you can understand the lowest value possible in cases where the maximum bitrate is not available or practical. For some users, 1 frame per second video might be considered an unacceptable video experience, so use caution when considering these bitrates.

Video Resolution Bandwidth

Video codec Resolution Maximum video payload bitrate (Kbps) Minimum video payload bitrate (Kbps)

RTVideo

Main Video CIF

250

50

RTVideo

Main Video VGA

600

350

RTVideo

Main Video HD

1500

800

RTVideo

Panoramic Video

350

50

Video FEC is included in the video payload bitrate when it is used so there are not separate values with video FEC and without video FEC.

Endpoints do not stream audio or video packets continuously. Depending on the scenario there are different levels of stream activity which indicate how often packets are sent for a stream. The activity of a stream depends on the media and the scenario, and does not depend on the codec being used. In a peer-to-peer scenario:

  • Endpoints send audio streams only when the users speak.
  • Both participants receive audio streams.
  • If video is used, both endpoints send and receive video streams during the entire call.

In a conferencing scenario:

  • Endpoints send audio streams only when the users speak.
  • All participants receive audio streams.
  • If video is used, only two endpoints send a video stream at a time (the active speaker and the previous active speaker).
  • If video is used, all participants receive video streams.

The following table shows stream activity levels based on measurements of customer data.

Stream Activity Levels

Scenario Media Estimated stream activity (%)

Peer-to-peer sessions

Audio

61

Peer-to-peer sessions

Main video CIF

84

Peer-to-peer sessions

Main video VGA

83

Peer-to-peer sessions

Main video HD

80

Peer-to-peer sessions

Panoramic video

74

Conferencing

Audio

43

Conferencing

Main video CIF

84

Conferencing

Main video VGA

83

Conferencing

Main video HD

80

Conferencing

Panoramic video

74

PSTN

Audio

65

In addition to the bandwidth required for the real-time transport protocol (RTP) traffic for audio and video media, bandwidth is required for real-time transport control protocol (RTCP). RTCP is used for reporting statistics and out-of-band control of the RTP stream. For planning, use the bandwidth numbers in the following table for RTCP traffic. These values represent the maximum bandwidth used for RTCP and differ between audio and video streams because of differences in the control data

RTCP Bandwidth

Media RTCP maximum bandwidth (Kbps)

Audio

5

Video

10

For capacity planning purposes, the following two bandwidths are of interest:

  • Maximum bandwidth without FEC   The maximum bandwidth that a stream will consume, including the typical activity of the stream and the typical codec used in the scenario without FEC. This is the bandwidth when the stream is at 100% activity and there is no packet loss triggering the use of FEC.  This is interesting for computing how much bandwidth must be allocated to allow the codec to be used in a given scenario. 
  • Maximum bandwidth with FEC   The maximum bandwidth that a stream consumes, including the typical activity of the stream and the typical codec used in the scenario with FEC. This is the bandwidth when the stream is at 100% activity and there is packet loss triggering the use of FEC to improve quality. This is interesting for computing how much bandwidth must be allocated to allow the codec to be used in a given scenario and allow the use of FEC to preserve quality under packet-loss conditions. 

The following tables also list an additional bandwidth value, Typical bandwidth. This is the average bandwidth that a stream consumes, including the typical activity of the stream and the typical codec used in the scenario. This bandwidth can be used for approximating how much bandwidth at any given time is being consumed by media traffic but should not be used for capacity planning, because individual calls will exceed this value when the activity level is higher than average.

The following tables provide these three bandwidth values for the various scenarios.

Audio/Video Capacity Planning for Peer-to-Peer Sessions

Media Codec Typical stream bandwidth (Kbps) Maximum stream bandwidth without FEC Maximum stream bandwidth with FEC

Audio

RTAudio Wideband

39.8

62

91

Audio

RTAudio Narrowband

29.3

44.8

56.6

Main video CIF

RTVideo

220

260

Not applicable

Main video VGA

RTVideo

508

610

Not applicable

Main video HD

RTVideo

1210

1510

Not applicable

Panoramic video

RTVideo

269

360

Not applicable

Audio/Video Capacity Planning for Conferences

Media Typical codec Typical stream bandwidth (Kbps) Maximum stream bandwidth without FEC Maximum stream bandwidth with FEC

Audio

G.722

46.1

100.6

164.6

Audio

Siren

25.5

52.6

68.6

Main video CIF

RTVideo

220

260

Not applicable

Main video VGA

RTVideo

508

610

Not applicable

Panoramic video

RTVideo

269

360

Not applicable

Audio Capacity Planning for PSTN

Media Typical codec Typical stream bandwidth (Kbps) Maximum stream bandwidth without FEC Maximum stream bandwidth with FEC

Audio

G.711

64.8

97

161

Audio

RTAudio Narrowband

30.9

44.8

56.6

The network bandwidth numbers in these tables represent one-way traffic only and include 5 Kbps for RTCP traffic overhead for each stream. For video the maximum video bit rate is used for computing the maximum stream.

 
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