HP ProCurve 530 NA (J8986A) Management And Configuration Manual page 160

Wireless Interface Configuration
Configuring the Radio
N o t e
N o t e
6-8
Getting to know 802.11a. The IEEE 802.11a provides specifications for
wireless ATM systems. It is also used in wireless hubs. Networks using 802.11a
operate at radio frequencies between 5.725 GHz and 5.850 GHz. The specifi-
cation uses a modulation scheme known as orthogonal frequency division
multiplexing (OFDM), which is especially well suited for use in office settings.
This standard supports data rates ranging from 6 to 54 Mbps.
The 802.11a mode is supported only on the access point's second radio (Radio
2).
Getting to know 802.11g and 802.11b. The IEEE 802.11b is a WLAN
standard often called Wi-Fi; it is backward-compatible with 802.11. Instead of
the phase-shift keying (PSK) modulation method historically used in 802.11
standards, 802.11b uses complementary code keying (CCK), which allows
higher data speeds and is less susceptible to multipath-propagation interfer-
ence.
The IEEE 802.11g offers transmission over relatively short distances at up to
54 megabits per second (Mbps), compared with the 11 Mbps theoretical
maximum of 802.11b. The 802.11g uses orthogonal frequency division multi-
plexing (OFDM), the modulation scheme used in 802.11a, to obtain higher data
speed. Computers or terminals set up for 802.11g can fall back to speeds of
11 Mbps, so that 802.11b and 802.11g devices can be compatible within a single
network.
To simultaneously support both 802.11g and 802.11b stations, the access point
uses a special "protected mode" operation as required for compliance with
the IEEE 802.11g standard. This mechanism has the effect of reducing the
maximum throughput for 802.11g stations in the network. Whenever 802.11b
stations are detected within range of the access point, the access point
experiences reduced throughput (even if the 802.11b stations are not active
in the network).
To achieve a higher throughput, you can configure the access point to
completely ignore the presence of 802.11b stations by changing the Advanced
"Web: Configuring Advanced Radio Settings" on page
radio settings. See
The 802.11g standard is backward-compatible with 802.11b. This backward-
compatibility allows it to use OFDM or CCK modulation.
To support both 802.11g and 802.11b stations, the access point must first
communicate with all stations using CCK and only switch to OFDM for data
transfers between 802.11g-compatible stations. This mechanism has the effect
of reducing the maximum throughput for 802.11g stations in the network.
6-14.