3Com is the latest company to offer tri-mode wireless Ethernet access points and client adapters, in a move which recognises that 802.11g at 54Mbit/s is proving rather more popular than 802.11a which offers the same speed but no backwards compatibility.

The new WLAN access points have slots for two WiFi cards, which 3Com says is important for flexibility. For example, it could have one 802.11a card and an 802.11g card which also supports the original 11Mbit/s 802.11b spec, or two 802.11g cards operating on different channels to provide more capacity for now, with the option to add 11a later.

"There's still more people using 11b because it's out there and services are available," said 3Com solutions marketing manager Bob Honour. "Now more companies are doing 11g so as certification happens, we will see prices of that drop fairly quickly and most of the market will go to 11g."

He said that 11a would only be used in niches, such as in locations where there was interference on the 2.4GHz frequency band used by both 11b and 11g. Several other things emit 2.4GHz radiation, such as microwave ovens, but 11a operates at 5GHz so it is immune to this.

Honour said that 3Com's devices did not suffer from the problem which afflicted some early 11g kit, where an 11b client joining the network forced 11g clients to drop to the lower speed. "We can even tie two channels together to give 108Mbit/s," he said, "although of course the total bandwidth is still shared across all the clients."

He added that the access points used the power-over-Ethernet standard, so they did not need separate power cables, and implemented both network login, which enables users to be assigned to specific virtual LANs, and the 802.11i security spec which includes AES hardware encryption.

The tri-mode access points are priced from $749, while a tri-mode wireless PC Card lists at $135. Honour said that the cards used 3Com's pop-out XJack antenna, which has the extra feature that when it is retracted, it turns the card off to save power.