Lync Bandwidth Requirements

The bandwidth requirements for Lync are difficult to determine for a given customer installation especially since the nature of Lync is to change how people communicate. The starting point for understanding the network bandwidth requirements are documented on Technet and Microsoft have released a bandwidth calculator.

The bandwidth usage is determined by a number of factors, the Codec used (along with overhead), the Stream activity level and for video, the resolution/quality and frame rate.

Audio Codec Bandwidth

Audio codec		Scenarios			Audio payload bitrate	Add IP header only	Also add UDP, RTP and SRTP	Also add FEC
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 rates are in Kbps (as are all bandwidth rates in this post) and assume 100% stream activity, which is not the normal case. (Note: The online Technet document shows KBPS (i.e. Kilo Bytes per second for the base Audio payload bitrate, it should be Kbps – reference Wikipedia)

Video Resolution Bandwidth

Video codec	Resolution	Maximum video payload bitrate	Minimum video payload bitrate
RTVideo	Main Video CIF	250	50
RTVideo	Main Video VGA	600	350
RTVideo	Main Video HD	1500	800
RTVideo	Panoramic Video	350	50

The maximum bitrate values shown (Kbps) are applicable for maximum frame rate and maximum quality. The minimum bitrate is for 1fps. HD Video is only available for peer-to-peer sessions. By default, only SD video is allowed, to allow HD video at Global or Site level use Set-CsMediaConfiguration –Identity:Global -MaxVideoRateAllowed HD720p15m

Bandwidth usage by participant

The raw bandwidth specified above is used only when the situation requires it, in other words, depending on what individual users are doing with the session determines their bandwidth requirements.

Peer-to-Peer

• 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.
  

Conference

• 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.
  

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

This is based on customer data gathered by Microsoft.

Added to the media bandwidth requirements is the requirement for control traffic in the form of Real Time Control Protocol (RTCP)

RTCP Bandwidth

Media	RTCP maximum bandwidth
Audio	5
Video	10

Overall Bandwidth by session type

Combining all this information together, Microsoft have come up with a table of maximum bandwidth utilisation (with and without FEC) and also typical bandwidth utilisation.

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

Media	Codec	Typical stream bandwidth	Maximum stream bandwidth without FEC	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	Maximum stream bandwidth without FEC	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	Maximum stream bandwidth without FEC	with FEC
Audio	G.711	64.8	97	161
Audio	RTAudio Narrowband	30.9	44.8	56.6