Installation guide

100
Wi-Fi Location-Based Services—Design and Deployment Considerations
OL-11612-01
RFID Tag Considerations
opening each tag casing and attaching a serial cable available from AeroScout. The tag activator is much
easier to use and saves a tremendous amount of time by allowing up to 50 tags to be configured and
activated simultaneously. The use of a tag activator eliminates disturbing the environmental seal of the
tag casing for configuration modifications (a potential concern if the asset tag is used in harsh
environments).
AeroScout tags do not associate to WLAN infrastructure during configuration, activation, or normal
location tracking operation.
The protocol analyzer trace in Figure 73 provides important information regarding how AeroScout T2
asset tags communicate and how the Cisco LBS solution recognizes and distinguishes AeroScout tags
from other devices. AeroScout tags transmit 30 byte 802.11 data frames on the preset channel and at the
interval determined by the beacon rate. At each tag beacon interval, the asset tag initiates Clear Channel
Assessment (CCA) for 100 microseconds. If the channel is clear, it then multicasts its payload for a
maximum of 500 microseconds at 1 Mbps. These frames are sent at 1 Mbps with the To Distribution
System (ToDS) and FromDS bits in the 802.11 MAC header both set to “1”. Note that the Wireless
Distribution System (WDS) four address frame format is being used, as shown by the
receiver/transmitter addresses shown in Figure 73. When the tag multicast address is recognized by the
Cisco UWN, the sender is identified as an AeroScout 802.11 active RFID tag and the content fields of
the packet are parsed, processed, and recorded into the location databases.
The AeroScout asset tag is capable of storing and transmitting various short messages from its onboard
ten message memory bank. At the current time, Cisco WCS does not display any of these messages nor
does it display tag status information beyond the reported onboard battery state of the tag. All
information displayed on WCS location floor maps (that is, asset names, groups and categories) are
configured and stored in WCS and are not part of the tag transmission.
Figure 73 Data Frame From AeroScout T2 Tag