Installation guide

22
Wi-Fi Location-Based Services—Design and Deployment Considerations
OL-11612-01
Cisco Location-Based Services Architecture
Figure 9 Information Flow for Asset Tag RSSI Data
Figure 9 summarizes the following events:
1. At each beacon interval, the asset tag transmits a ~30 byte L2 multicast on its configured channels.
2. At least three (and preferably four or five) access points detect the asset tag transmission. It is a
multicast transmission and is forwarded to the WLAN controller (WLC) to which the detecting
access points are registered.
3. The WLC stores the battery status information associated with the asset tag in an internal table
indexed by the asset tag MAC address.
4. For each registered AP, the WLC also places the following asset tag information in an internal table:
– Tag MAC address
– AP MAC address
– AP interface
– RSSI measurement
5. The location server periodically polls the WLC for the contents of the asset tag tables using SNMP.
6. The location server calculates the location of the asset tag using the RSSI information contained in
the SNMP responses and stores the updated information in the location server database.
7. The location server dispatches any asynchronous notification events based on the updated asset tag
location to configured notification recipients.
8. Location end users make use of WCS (or another location client) to request location information
based on floor maps or search criteria. A request for location information is made from the location
to the location server via a SOAP/XML online query.
WCS and the location appliance exchange information regarding calibration maps and network designs
during a process known as synchronization. During a network design synchronization between WCS and
the location appliance, the up-to-date partner updates the design and calibration information of the
out-of-date partner. The location appliance synchronizes with each controller containing access points
190541
Multicast Packet
from Tag
WLC
Tag information
indexed by Tag
MAC Address and
Tag RSSI values
reported by each AP
LWAPP AP
Location
Appliance
Location
Database
WCS
Multicast packets
sent to WLC
SNMP Poll
for Tag data
Calculate location from raw
RSSI information and store
On-demand
SOAP/XML Query
Asynchronous
notifications