OCS 2007 RealTime (RT) codecs

There is some debate in the industry about bandwidth requirements for Microsoft’s RTAudio and RTVideo codec used in Office Communication Server 2007. This is a very good description of the actually requirements for planning purposes.

The short answer is that you should plan 57 Kbps for Audio and 320 Kbps for Video. The QoE document lists 45 Kbps for RTA-WB, but that does not include Ethernet or SRTP overhead.

OC 2007 client uses RTAudio Wideband encoded at an average bit rate of 29 kbps in 20 ms packets. By default OC 2007 calls are encrypted using SRTP, the per-packet overhead is approximately Ethernet II = 14 byte header + 4 byte footer, IP = 20 byte header, UDP = 8 byte header, RTP = 12 byte header, SRTP = 12 byte footer. These numbers are the typical size for these headers.This results in 70 bytes per packet overhead per packet sent. With payload at 29 kbps at 20ms packets, the average network bit rate for a fully utilized voice channel in a point to point call is:
(70 [bytes/packet] * [8 bits/byte] * 50 [packet/s]) + 29000 [bits/s] = 57 kbps

In the web conference scenario with Round Table device, each user will consume 320Kbps for Active Speaker, 320Kbps for paranomic video and 48Kbps for Audio…….In Audio and Video conference, Audio codec is Siren so the bandwidth requirement for Audio is a little bit less.

Codec Min Bandwidth Max Bandwidth Planning Rate
RealTime Audio (RTA-WB ) 24 Kbps 74 Kbps 57 Kbps
Siren 22 Kbps 48 Kbps 48 Kbps
RealTime Video (VC-1) 50 Kbps 320 Kbps 320 Kbps

UM voice message storage codecs

Voice message storage codec Bits Compressed file?
WMA 16 bit Yes
G.711 PCM 16 bit No
GSM 06.10 8-bit Yes

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