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Cisco 2700 Series Wireless Location Appliance Deployment Guide
OL-8478-01
lightweight access points. This appliance tracks any Wi-Fi device, including Wi-Fi clients,
standards-based Wi-Fi active RFID tags, rogue access points, and clients. It was designed with the
following requirements in mind:
•Manageability—The same browser-based interface that is used for the Cisco WCS is also used for
the appliance. Moreover, the location appliance integrates directly into the wireless LAN
architecture, providing one unified network to manage instead of multiple disparate wireless
networks.
•Scalability —The appliance was built to simultaneously track up to 1500 wireless devices. WCS can
manage multiple location appliances for greater scalability.
•Security—The controller, WCS, and the location appliance were separated to deliver the most secure
architecture possible. The appliance records historical location information that can be used for
audit trails and regulatory compliance.
•Open and standards based—The appliance has a SOAP/XML API that can be integrated by partners
with other business applications and can track any standards.
•Easy deployment of business applications—The appliance can be integrated with new business
applications such as asset tracking, inventory management, location-based security, or automated
workflow management.
Location Tracking
The location appliance calculates the location of tracked devices using RF fingerprinting. This technique
uses RF characteristics such as reflection, attenuation, and multi-path to impact signal strength readings
of devices in specific environments.
To detect the RF signal at each location in an enterprise, the system must first understand how the RF
interacts with an installation's environmental variables, such as building materials, walls, doors, and
furniture. As such, an RF calibration is required (post wireless LAN installation) to determine the
characteristics of that specific RF environment.
When an RF calibration is performed, the attenuation of walls and other building characteristics is taken
into account. The extent of RF reflection and multi-path is also calculated for every coordinate, or grid,
on a floor map in the management system for each access point. For a single point on the grid, many
different access points detect devices; however, each access point detects these devices at different signal
strengths.
At the conclusion of calibration, a database is populated inside of the management system. That database
contains each coordinate and how each access point views that coordinate from the standpoint of signal
strength.
When devices' locations are requested by the management system, each controller replies on behalf of
its access points with the signal strengths at which they detect them. The management system then
matches the information it gathers from the controllers against its database of location RF fingerprints.
Devices' locations are then plotted visually on a floor map.
Performing a Calibration
You can generate the location of coordinates of tracked devices by using prediction. The location
coordinates generated in this case are predicated from RF models that the engine already has in its
knowledge base. However, if the location resolution is not within specifications, it can be further tuned
using a technique known as calibration.