Installation guide

Wi-Fi Location-Based Services—Design and Deployment Considerations

OL-11612-01

RFID Tag Considerations

readers themselves is possible because of their use of industry standard 802.11 client radios. Because of

this, these portable readers would be treated just as other WLAN clients and indicated on floor maps by

a blue rectangular icon.

Figure 66 Portable RFID Interrogators with Integrated Wi-Fi Uplink

Using 802.11b Tags in an 802.11g Environment

A common question that often arises has to do with the performance impact of an 802.11b asset tag in a

network that otherwise consists of all 802.11g clients and access points. The crux of such discussions is

typically centered around whether or not protection mechanisms (such as RTS-CTS or CTS-to-self) are

initiated by the 802.11g network to assure compatibility between the 802.11b asset tags and the 802.11g

network. Such protection mechanisms have the potential for adding overhead and negatively impacting

the hi-speed performance of 802.11g clients.

Note For an excellent explanation of 802.11g performance, capacity, and the impact of protection

mechanisms, see “Capacity, Coverage and Deployment Considerations for IEEE 802.11g” at the

following URL:

http://www.cisco.com/en/US/products/hw/wireless/ps430/products_white_paper09186a00801d61a3.sh

tml.

A popular point of contention is whether these protection mechanisms are initiated on one of the

following:

• Τhe mere appearance of an 802.11b asset tag that is issuing multicasts or probe requests to the

network

• Only on the active association of the asset tag to the wireless infrastructure

Laboratory research and analysis has shown that protection mechanisms are not initiated throughout an

entire network of access points if an 802.11b asset tag or WLAN client is merely powered on. In fact,

the following has been observed:

• A probe request from an 802.11b asset tag that is not associated to any access point on a particular

channel does not in and of itself cause the initiation of protection mode by an 802.11g access point

that detects it.

• Protection mode is not initiated until the 802.11b asset tag successfully associates to either the cell

in question or an adjacent cell on the same channel. At that point, the target cell as well as any other

cells on the same channel and RF-adjacent to the target cell initiate protection mode.