Example: Gathering the Required Information for Call Admission Control

 

Topic Last Modified: 2011-08-18

Let’s walk through an example of how to plan for and implement call admission control (CAC). At a high level, this consists of the following activities:

1. Identify all of your network hubs and backbones (called network regions in this guide).

2. Identify the Lync Server central site that will manage CAC for each network region.

3. Identify and define the network sites that are connected to each network region.

4. For each network site whose connection to the WAN is bandwidth-constrained, describe the bandwidth capacity of the WAN connection and the bandwidth limits that to the network administrator has set for Lync Server media traffic, if applicable. You do not need to include sites whose connection to the WAN is not bandwidth-constrained.

5. Associate each subnet in your network with a network site.

6. Map the links between the network regions. For each link, describe its bandwidth capacity and any limits that the network administrator has placed on Lync Server media traffic.

7. Define a route between every pair of network regions.

Gather the Required Information

To prepare for call admission control, gather the information described in the following steps:

1. Identify your network regions. A network region represents a network backbone or a network hub.

   A network backbone or a network hub is a part of computer network infrastructure that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnets. A backbone can tie together diverse networks, from a small location to a wide geographic area. The backbone's capacity is typically greater than that of the networks connected to it.

   Our example topology has three network regions: North America, EMEA, and APAC. A network region contains a collection of network sites. Work with your network administrator to define the network regions for your enterprise.

2. Identify each network region’s associated central site. A central site contains at least one Lync Server 2010 Front End Server and is the Lync Server deployment that will manage CAC for all media traffic that passes through the network region’s WAN connection.

   An example enterprise network divided into three network regions

   

   Note

   A Multiprotocol Label Switching (MPLS) network should be represented as a network region in which each geographic location has a corresponding network site. For details, see the “Call Admission Control on an MPLS Network” topic in the Planning documentation.

   In the preceding example network topology, there are three network regions, each with a Lync Server central site that manages CAC. The appropriate central site for a network region is chosen by the geographic vicinity. Because media traffic will be heaviest within network regions, the ownership by geographic vicinity makes it self-contained and will continue to be functional even if other central sites become unavailable for any reason.

   In this example, a Lync Server deployment named Chicago is the central site for the North America region.

   All Lync Server users in North America are homed on servers in the Chicago deployment. The following table shows central sites for all three network regions.

   Network Regions and their Associated Central Sites

   Network Region	Central Site
   North America	Chicago
   EMEA	London
   APAC	Beijing

   Note

   Depending on your Lync Server topology, the same central site can be assigned to multiple network regions.

3. For each network region, identify all of the network sites (offices or locations) whose WAN connections are not bandwidth-constrained. Because these sites are not bandwidth constrained, you do not need to apply CAC bandwidth policies to them.

   In the example shown in the following table, three network sites do not have bandwidth-constrained WAN links: New York, Chicago, and Detroit.

   Network Sites not Constrained by WAN Bandwidth

   Network Site	Network Region
   New York	North America
   Chicago	North America
   Detroit	North America

4. For each network region, identify all of the network sites that connect to the network region through bandwidth-constrained WAN links.

   To ensure audio and video quality, we recommend that these bandwidth-constrained network sites have their WANs monitored and CAC bandwidth policies that limit media (voice or video) traffic flow to and from the network region.

   In the example shown in the following table, there are three network sites that are constrained by WAN bandwidth: Portland, Reno and Albuquerque.

   Network Sites Constrained by WAN Bandwidth

   Network Site	Network Region
   Albuquerque	North America
   Reno	North America
   Portland	North America

   CAC network region North America with three network sites that are unconstrained by bandwidth (Chicago, New York, and Detroit) and three network sites that are constrained by WAN bandwidth (Portland, Reno, and Albuquerque)

   

5. For each bandwidth-constrained WAN link, determine the following:

   • Overall bandwidth limit that you want to set for all concurrent audio sessions. If a new audio session will cause this limit to be exceeded, Lync Server does not allow the session to start.

   • Bandwidth limit that you want to set for each individual audio session. The default CAC bandwidth limit is 175 kbps, but it can be modified by the administrator.

   • Overall bandwidth limit that you want to set for all concurrent video sessions. If a new video session will cause this limit to be exceeded, Lync Server does not allow the session to start.

   • Bandwidth limit that you want to set for each individual video session. The default CAC bandwidth limit is 700 kbps, but it can be modified by the administrator.

   Network Sites with WAN Bandwidth Constraint Information (Bandwidth in kbps)

   Network Site	Network Region	BW Limit	Audio Limit	Audio Session Limit	Video Limit	Video Session Limit
   Albuquerque	North America	5,000	2,000	175	1,400	700
   Reno	North America	10,000	4,000	175	2,800	700
   Portland	North America	5,000	4,000	175	2,800	700
   New York	North America	(no limit)	(no limit)	(no limit)	(no limit)	(no limit)
   Chicago	North America	(no limit)	(no limit)	(no limit)	(no limit)	(no limit)
   Detroit	North America	(no limit)	(no limit)	(no limit)	(no limit)	(no limit)

6. For every subnet in your network, specify its associated network site.

   Important

   Every subnet in your network must be associated with a network site, even if the network site is not bandwidth constrained. This is because call admission control uses subnet information to determine at which network site an endpoint is located. When the locations of both parties in the session are determined, call admission control can determine if there is sufficient bandwidth to establish a call. When a session is established over a link that has no bandwidth limits, an alert is generated.
   If you deploy Audio/Video Edge Servers, the public IP addresses of each Edge Server must be associated with the network site where the Edge Server is deployed. Each public IP address of the A/V Edge Server must be added to your network configuration settings as a subnet with a subnet mask of 32. For example, if you deploy A/V Edge Servers in Chicago, then for each external IP address of those servers create a subnet with a subnet mask of 32 and associate network site Chicago with those subnets. For details about public IP addresses, see Determining External A/V Firewall and Port Requirements in the Planning documentation.

   Note

   A Key Health Indicator (KHI) alert is raised, specifying a list of IP addresses that are present in your network but are either not associated with a subnet, or the subnet that includes the IP addresses is not associated with a network site. This alert will not be raised more than once within an 8 hour period. The relevant alert information and an example are as follows:
   Source: CS Bandwidth Policy Service (Core)
   Event number: 36034
   Level: 2
   Description: The Subnets for the following IP Addresses: <List of IP Addresses> are either not configured or the subnets are not associated to a Network Site.
   Cause: The Subnets for the corresponding IP addresses are missing from the network configuration settings or the Subnets are not associated to a network site.
   Resolution: Add Subnets corresponding to the preceding list of IP addresses into the network configuration settings and associate every Subnet to a Network Site.
   For example, if the IP address list in the alert specifies 10.121.248.226 and 10.121.249.20, either these IP addresses are not associated with a subnet or the subnet they are associated with does not belong to a network site. If 10.121.248.0/24 and 10.121.249.0/24 are the corresponding subnets for these addresses, you can resolve this issue as follows:

   1. Ensure that IP address 10.121.248.226 is associated with the 10.121.248.0/24 subnet and IP address 10.121.249.20 is associated with the 10.121.249.0/24 subnet.

   2. Ensure that the 10.121.248.0/24 and 10.121.249.0/24 subnets are each associated with a network site.

   Network Sites and Associated Subnets (Bandwidth in kbps)

   Network Site	Network Region	BW Limit	Audio Limit	Audio Session Limit	Video Limit	Video Session Limit	Subnets
   Albuquerque	North America	5,000	2,000	175	1,400	700	172.29.79.0/23, 157.57.215.0/25, 172.29.90.0/23, 172.29.80.0/24
   Reno	North America	10,000	4,000	175	2,800	700	157.57.210.0/23, 172.28.151.128/25
   Portland	North America	5,000	4,000	175	2,800	700	172.29.77.0/24 10.71.108.0/24, 157.57.208.0/23
   New York	North America	(no limit)	(no limit)	(no limit)	(no limit)	(no limit)	172.29.80.0/23, 157.57.216.0/25, 172.29.91.0/23, 172.29.81.0/24
   Chicago	North America	(no limit)	(no limit)	(no limit)	(no limit)	(no limit)	157.57.211.0/23, 172.28.152.128/25
   Detroit	North America	(no limit)	(no limit)	(no limit)	(no limit)	(no limit)	172.29.78.0/24 10.71.109.0/24, 157.57.209.0/23

7. In Lync Server 2010 call admission control, the connections between network regions are called region links. For each region link, determine the following, just as you did for the network sites:

   • Overall bandwidth limit that you want to set for all concurrent audio sessions. If a new audio session will cause this limit to be exceeded, Lync Server does not allow the session to start.

   • Bandwidth limit that you want to set for each individual audio session. The default CAC bandwidth limit is 175 kbps, but it can be modified by the administrator.

   • Overall bandwidth limit that you want to set for all concurrent video sessions. If a new video session will cause this limit to be exceeded, Lync Server does not allow the session to start.

   • Bandwidth limit that you want to set for each individual video session. The default CAC bandwidth limit is 700 kbps, but it can be modified by the administrator.

   Network Region links with associated bandwidth limits

   

   Region Link Bandwidth Information (Bandwidth in kbps)

   Region Link Name	First Region	Second Region	BW Limit	Audio Limit	Audio Session Limit	Video Limit	Video Session Limit
   NA-EMEA-LINK	North America	EMEA	50,000	20,000	175	14,000	700
   EMEA-APAC-LINK	EMEA	APAC	25,000	10,000	175	7,000	700

8. Define a route between every pair of network regions.

   Note

   Two links are required for the route between the North America and APAC regions because there is no region link that directly connects them.

   Region Routes

   Region Route Name	First Region	Second Region	Region Links
   NA-EMEA-ROUTE	North America	EMEA	NA-EMEA-LINK
   EMEA-APAC-ROUTE	EMEA	APAC	EMEA-APAC-LINK
   NA-APAC-ROUTE	North America	APAC	NA-EMEA-LINK, EMEA-APAC-LINK

9. For every pair of network sites that are directly connected by a single link (called an inter-site link), determine the following:

   • Overall bandwidth limit that you want to set for all concurrent audio sessions. If a new audio session will cause this limit to be exceeded, Lync Server does not allow the session to start.

   • Bandwidth limit that you want to set for each individual audio session. The default CAC bandwidth limit is 175 kbps, but it can be modified by the administrator.

   • Overall bandwidth limit that you want to set for all concurrent video sessions. If a new video session will cause this limit to be exceeded, Lync Server does not allow the session to start.

   • Bandwidth limit that you want to set for each individual video session. The default CAC bandwidth limit is 700 kbps, but it can be modified by the administrator.

   CAC network region North America showing the bandwidth capacities and bandwidth limits for the inter-site link between Reno and Albuquerque

   

   Bandwidth Information for an Inter-Site Link between Two Network Sites (Bandwidth in kbps)

   Inter-Site Link Name	First Site	Second Site	BW Limit	Audio Limit	Audio Session Limit	Video Limit	Video Session Limit
   Reno-Albu-Intersite-Link	Reno	Albuquerque	20,000	12,000	175	5,000	700

Next Steps

After you have gathered the required information, you can perform CAC deployment either by using the Lync Server Management Shell or Lync Server Control Panel.

Note

Although you can perform most network configuration tasks by using Lync Server Control Panel, to create subnets and inter-site links, you must use Lync Server Management Shell. For details, see the Lync Server Management Shell documentation for the New-CsNetworkSubnet and New-CsNetworkIntersitePolicy cmdlets.