Installation guide

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Wi-Fi Location-Based Services—Design and Deployment Considerations
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Deployment Best Practices
Figure 54 Enabling Location Server Polling on WCS
Polling should never be arbitrarily enabled across all categories, especially in situations where
controllers are deployed remotely across highly used or slow WAN links. Instead, enable polling only
for devices that are truly of interest. When controllers must respond to unnecessary polling requests
network bandwidth as well as controller and location appliance CPU cycles are wasted.
For slower networks, the default timeout value of 5 seconds can be raised to increase the length of time
the location appliance waits for a response from a WLAN controller. In cases where there is a high
degree of packet loss across the network, the default number of retries can also be increased. Under these
conditions, such modifications may improve the ability of the location appliance to retrieve data
successfully from polled WLAN controllers.
There are tradeoffs that must be kept in mind when determining polling intervals for devices categories
of interest. The more aggressive the polling interval, the higher the potential for more timely location
reporting. The tradeoff, however, is that shorter polling intervals are accompanied by increased
controller-to-location server traffic and controller CPU utilization. When deciding on what is an
appropriate polling interval, consider all device-specific characteristics that may impact your decision.
For example, L2 multicasting asset tags are not constantly transmitting but tend to transmit their
multicast payloads at every beacon interval. For these types of devices, Cisco does not recommend that
a polling interval be set shorter than the beacon interval (see Enable Asset Tag Polling on the Location
Appliance, page 96 for an example of this with AeroScout asset tags).
Thus far, two factors affecting the level of traffic observed between the location appliance and a WLAN
controller have been established: (a) the tracked devices the location server is configured to poll and (b)
the rate of polling. Of course, increasing the number of WLAN controllers and tracked devices also
increases the amount of polling traffic. The greater the number of controllers to be polled, the greater
the number of SNMP Get requests that are issued by the location appliance. Lab testing indicates that
for a constant population of tracked devices, the amount of traffic generated is higher when these devices
were distributed among a greater number of smaller capacity controllers rather than when the devices
were consolidated onto fewer but larger capacity controllers. This appears to be primarily because of the
increased number of SNMP requests being issued by the location appliance along with the higher