Quality of Service (QoS) for Lync 2010 and Lync 2013

Microsoft have published a lot of documentation about Quality of Service (QoS) with Lync. There is the Word document Enabling Quality of Service with Microsoft Lync Server 2010, TechNet for QoS on Lync 2010 and TechNet for QoS on Lync 2013. From what I can see there are no QoS specific changes between Lync 2010 and Lync 2013, other than the documentation seems to have been improved – especially for the client QoS section.

As there is so much documentation and no hard recommendations it can seem a bit overwhelming. Elan Shudnow has two comprehensive posts on QoS 1 and 2 but combine these with the Microsoft documentation there is a bit of information overload. The purpose of this post is a simple (relative term) summary of the changes required to enable QoS.

Microsoft Recommended QoS Markings

QoS marking is performed by the endpoints involved in the conversation – Lync clients, Lync Front-End servers, Lync Mediation servers, Lync phones and media gateways. This is done by setting a Differentiated Services Code Point (DSCP) marking on the TCP/IP packets as they are processed by the endpoint. The table below shows the recommended QoS markings for Lync. There are other recommendations for application sharing and file transfer, but the focus of QoS for Lync is to ensure the Audio traffic is prioritised highest, while also prioritising Video and SIP signalling.

Media Type	Classification	Queuing and Dropping	Notes
Audio	EF (DSCP 46)	Priority Queue	Low loss, low latency, low jitter, assured bandwidth (BW)
Video	AF41 (DSCP 34)	BW Queue + DSCP WRED	Pair with WAN Bandwidth Policies on constrained links
SIP Signalling	CS3 (DSCP 24)	BW Queue	Class 4. Low drop priority

Note: The DSCP markings in the following steps should be mapped to what the switches and routers are prioritising if different from the recommendations above.

Step 1 – Decide on the port ranges

In order to mark audio traffic as DSCP 46 and video traffic as DSCP 34, we need to ensure Lync restricts each modality to a specific set of ports that do not overlap. Windows can then set the QoS DSCP markings on traffic based on specific port numbers and potentially from specific programs on those port numbers. Based on the documentation above and Elan’s examples, the table below seems to be a good mix of keeping most settings default and ensuring no overlapping port ranges.

Scenario	Starting port	Ending port
Client audio	20000	20039
Client video	20040	20079
Client application sharing	20080	20119
Server application sharing	40803	49151
Server audio	49152	57500
Server video	57501	65535

Step 2 – Set the Port Ranges (Lync in band settings)

Client Ranges

Set-CsConferencingConfiguration -ClientMediaPortRangeEnabled 1 Set-CsConferencingConfiguration -ClientAudioPort 20000 -ClientAudioPortRange 40 -ClientVideoPort 20040 -ClientVideoPortRange 40 -ClientAppSharingPort 20080 -ClientAppSharingPortRange 40 -ClientFileTransferPort 20120 -ClientFileTransferPortRange 40 -ClientMediaPort 20160 -ClientMediaPortRange 40

Lync Pools

Set-CsConferenceServer -Identity <PoolFQDN> -AppSharingPortStart 40803 -AppSharingPortCount 8348 Set-CsApplicationServer -Identity <PoolFQDN> -AppSharingPortStart 40803 -AppSharingPortCount 8348

Lync Phone

Set-CsUCPhoneConfiguration -identity global -VoiceDiffServTag 46

Step 3 – Group Policy for Clients

A Group Policy should be created to set the following Policy Based QoS settings (applicable to Windows 8, Windows 7 and Vista):

• Voice: DSCP 46 for ‘communicator.exe’ (OCS or Lync 2010) or ‘lync.exe’ (Lync 2013) on source TCP/UDP ports 20000:20039
• Video: DSCP 34 for ‘communicator.exe’ (OCS or Lync 2010) or ‘lync.exe’ (Lync 2013) on source TCP/UDP ports 20040:20079

Step 4 – Group Policy for Servers

A Group Policy should be created to set the following Policy Based QoS settings:

Lync Front-End servers and standalone A/V Conferencing servers

• Voice: DSCP 46 for all applications on source TCP/UDP ports 49152:57500
• Video: DSCP 34 for all applications on source TCP/UDP ports 57501:65535

Lync Mediation servers and SBAs

• Voice: DSCP 46 for all applications on source TCP/UDP ports 49152:57500

In order to confirm the Group Policies have been applied to the servers you can use regedit to viewHKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Windows\QoS\ which should look similar to this:

Step 5 – Local Computer Policy for Edge Servers

Lync Edge Servers are not domain joined so cannot use Group Policy. A Local Security Policy should be created to set the following Policy Based QoS settings by running gpedit.msc:

• Client voice:   DSCP 46 for MediaRelaySvc.exe on destination TCP/UDP ports 20000:20039
• Server voice:  DSCP 46 for MediaRelaySvc.exe on destination TCP/UDP ports 49152:57500
• Client video:  DSCP 34 for MediaRelaySvc.exe on destination TCP/UDP ports 20040:20079
• Server video: DSCP 34 for MediaRelaySvc.exe on destination TCP/UDP ports 57501:65535

Note: The Edge Policy Based QoS is using Destination port numbers, not source like the previous Group Policies

The Edge Local Computer Policy should look similar to this:

Step 6 – Set Voice Gateways to mark correct DSCP values

This is dependent on the gateway vendor, but ensure the gateway is setting the same DSCP markings for audio defined above.

Finished

Assuming traffic prioritisation has been set on all routers / switches in the media path, that should be all that is required. For more information on how to confirm the DSCP markings are being applied, see the blog by Jeff Schertz on QoS.