Jens Trier Rasmussen

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Bandwidth Management

Bandwidth Management

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(Updated Oct 15 to fix misunderstanding around how EnableBWPolicyOverride works)

In this post I will show you how to configure CAC or bandwidth management and describe how the user experience will be when making calls where no bandwidth is available.

Imagine the setup below. Two network segments ( and with a router between. Two sites in the topology – Copenhagen and Odense. One user, a Lync Server 2010 SE box and a PSTN Gateway on both segments and the the user is signed in to the local SE box. Both users are UM enabled in a dial plan hosted on the Exchange 2010 SP1 server in Copenhagen.


I want to configure CAC to disable all audio and video between Copenhagen and Odense. In order to do that I use the PS script below:

# Bandwidth PolicyProfile
New-CsNetworkBandwidthPolicyProfile -Identity AllBlocked -AudioBWLimit 0 -AudioBWSessionLimit 200 -VideoBWLimit 0 -VideoBWSessionLimit 3000

# Network Regions
New-CsNetworkRegion -NetworkRegionID DK1 –CentralSite site:cph1 -Description "Copenhagen"
New-CsNetworkRegion -NetworkRegionID DK2 –CentralSite site:od1 -Description "Odense"

# Network Region Links
$a=New-CsNetworkRegionLink -NetworkRegionLinkID rl1 -NetworkRegionID1 DK1 -NetworkRegionID2 DK2 -BWPolicyProfileId AllBlocked

# Network InterRegion Routes
New-CsNetworkInterRegionRoute -InterNetworkRegionRouteID nr1 -NetworkRegionLinks $a.identity -NetworkRegionID1 DK1 -NetworkRegionID2 DK2

# Creates a new CsNetworkSite and assigns that the bandwidth policy we just created
New-CsNetworkSite -NetworkSiteID Cph -Description "Copenhagen" -NetworkRegionID DK1
New-CsNetworkSite -NetworkSiteID Od -Description "Odense" -NetworkRegionID DK2

# Create new CsNetworkSubnets
New-CsNetworkSubnet -SubnetID -MaskBits 24 -Description "Copenhagen" -NetworkSiteId Cph
New-CsNetworkSubnet -SubnetID -MaskBits 24 -Description "Odense" -NetworkSiteId Od

# Setup bandwidth management
Set-CsNetworkConfiguration –EnableBandwidthPolicyCheck $true

Let’s assume that the above configuration is in effect and that Alice would like to call Bob. There is not enough bandwidth available to setup the call and the call experience of Alice and Bob is therefore controlled by two parameters (EnableBWPolicyOverride and AllowPSTNReRouting) in the voice policy, they have been granted.

If a user has EnableBWPolicyOverride = True calls to the person will not be subject to bandwidth restrictions. If a user has AllowPSTNRerouting calls he/she makes are allowed to be re-routed via PSTN. In the table below I’ve described what the call experience will be given different values for the two parameters.


Alice voice policy

Bob voice policy


Alice calls Bob

AllowPSTNReRerouting = False

EnableBWPolicyOverride = False

Since Alice has AllowPSTNReRouting = False and Bob has EnableBWPolicyOverride = False the call is being sent directly to Exchange UM and Alice can leave a voice mail for Bob

Alice calls Bob

AllowPSTNReRerouting = False

EnableBWPolicyOverride = True

Since Alice has AllowPSTNReRouting = False and Bob has EnableBWPolicyOverride = True the call is going directly to Bob

Alice calls Bob

AllowPSTNReRerouting = True

EnableBWPolicyOverride = False

Since Alice has AllowPSTNReRouting = True and Bob has EnableBWPolicyOverride = False the call is being routed out the PSTN gateway in Copenhagen and in to the PSTN gateway in Odense

Alice calls Bob

AllowPSTNReRerouting = True

EnableBWPolicyOverride = True

Since Alice has AllowPSTNReRouting = True and Bob has EnableBWPolicyOverride = True the call is going directly to Bob

  • Hello Jens, as I do to limit the band locally? My IP range is and when I connect my client Lync with the Polycom HDX 8000 is the width of the band at 1920 Kbps. If you have any tips or any specific site, thank you.

    Jens: Only tip I can provide is this article, which might give you some ideas.

  • Thanks, your tip I helped solve my problem.

  • I only don't do the CAC to work with HDX8000

  • Hello Jens,

    In case the Exchange UM server is located on the Odense site and we are having the first scenario: Alice has AllowPSTNReRerouting = False and Bob EnableBWPolicyOverride = False.

    According to this scenario, the call is routed to Bob's Voice mail directly. As the Exchange UM server is located on Odense site... So the call is traversing the WAN. That scenario may not be what we want to have.

    Is there a way to disable all kind of reroute: Can we have a policy that simply disconnects the call if the CAC threshold is reached?


    Jens>No, AFAIK you can't prevent the call going to voice mail, if the user is enabled for voice mail. You MIGHT be able to use new-csvoicemailreroutingconfiguration to re-route the call via PSTN, but I'm not sure and haven't tried it.

  • Hi Jens, below link is broken can you check,

    Jens>New link

  • Jens, when I configure similar settings like in you example, I get an error message when enabling CAC: There is no internetworkregionroute between DK2 and DK1. I suppose these routes are two-way, ie when you configure New-CsNetworkInterRegionRoute -InterNetworkRegionRouteID nr1 -NetworkRegionLinks $a.identity -NetworkRegionID1 DK1 -NetworkRegionID2 DK2 it is for the other way around as well? So in other words what will happen when Bob calls Alice?

    Jens>Yes, it should be both ways. I just re-ran those commands on Lync 2013 February Update and they worked.

  • Does CAC work between sites of the same region then?(Between regions yes, there is an interlink between regions and alternate route).

    I might have sites with different link capacities and so don't want every link the region to enforce the same bandwidth caps and checks?

    I may be missing a basic understanding here, but any advice would be appreciated


    Jens>I asked my colleague Thomas and here is what he told me: A site is always part of a region – optionally you can assign a bandwidth policy to a site. If you do so, all calls between
    the region and this site will apply CAC based on this policy. If you have two different sites attached to a region and both have CAC policies assigned, CAC will be applied based on both the policies: the bandwidth limit will be set based on the lowest allowed bandwidth maximum and the call will be only allowed if all links between the sites have sufficient bandwidth. The same applies if the sites are attached to different regions: all links between the sites will be checked for bandwidth and policies will be applied.

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