HP AirProtect Security Software manual 113 3Com AirProtect Planner User Guide

Appendix D: Glossary of Terms

802.11g Wireless Protocol

802.11n Wireless Protocol

MIMO configuration	Multiple-Input-Multiple-
	Output configuration

Channel width

Guard Interval (GI)

802.11b supports bandwidth up to 11 Mbps.

802.11b uses the same radio signaling frequency

–2.4 GHz, as the original 802.11 standard. Being an unregulated frequency, 802.11b gear can incur interference from microwave ovens, cordless phones, and other appliances using the same 2.4 GHz range. However, you can easily avoid interference by installing 802.11b gear at a reasonable distance from other appliances. Vendors often prefer using unregulated frequencies to lower their production costs.

In 2002 and 2003, WLAN products supporting a new standard called 802.11g began to appear on the scene. 802.11g attempts to combine the best of both 802.11a and 802.11b. 802.11g supports bandwidth up to 54 Mbps, and it uses the 2.4 GHz frequency for greater range. 802.11g is backwards compatible with 802.11b, which means that 802.11g APs will work with 802.11b Wireless Network Adapters and vice versa.

This is an emerging standard for wireless local area networks that promises higher data rates and longer range as compared to its predecessors 802.11a, b, and g. 802.11n brings many new features at the medium access control and physical layers (for example, multiple-input- multiple-output (MIMO), wider 40 MHz channels, frame aggregation).

Multiple-Input-Multiple-Output (MIMO) stands for multiple radio chains at the transmitter and receiver, often depicted as n x m, where n is the number of transmitting radios and m is the number of receiving radios. MIMO can be leveraged in many ways for increasing the range of a WLAN using spatial diversity and for increasing the data transmission rate using spatial multiplexing. Spatial diversity is achieved by transmitting or receiving copies of the same signal over multiple radios. Spatial multiplexing is achieved by transmitting and receiving unique data streams over multiple radios. The maximum number of spatial streams is limited by min (n, m), that is, the minimum among the number of radio chains at the transmitter and receiver. IEEE 802.11n draft 2.0 makes it mandatory for APs to support a minimum of two spatial streams and support for up to four streams optionally.

Legacy 802.11 protocols operate on 20 MHz channels. IEEE 802.11n allows bonding of two 20 MHz channels so that a net channel width of 40 MHz can be used. In 40 MHz mode, one channel is assigned as the “primary” channel and the other is assigned as the “secondary” channel. The secondary channel is identified as “upper” or “lower” with respect to the primary channel. For example, in 2.4 GHz, if channel 6 is the primary channel then channel 10 could be assigned as the upper secondary and channel 2 as the lower secondary channel.

The guard interval is the spacing between consecutive symbol transmissions. IEEE 802.11n draft 2.0 prescribes a mandatory long Guard Interval of 800 ns and an optional short Guard Interval of 400 ns.

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3Com ® AirProtect Planner User Guide