The Long and the Short of It

We, the people, deserve compatible wireless access. And when it comes to the 802.11b Wi-Fi standard, we usually get it, with a niggling caveat.

This minor headache centers on the preamble, which is the part of the 802.11 specification that deals with how packets are sent and received over the airwaves. The IEEE 802.11 committee specified a long preamble so that 802.11b wireless LANs could interoperate with 802.11 DSSS networks that run at 1M bps to 2M bps. According to Al Petrick, vice president of the 802.11 committee, a short preamble was also specified, but it was intended to be a “turbo” mode “for those devices and applications requiring higher throughput in a network.”

Of course, the two are incompatible, and thats why 802.11 specified the default to be the long preamble. The vendors of 802.11 equipment, meanwhile, probably wanting that equipment to look speedier than it actually was, began defaulting to short preambles.

Now it seems that at least half the vendors default to short preambles. Intel is one such culprit, and Ive also received units from 3Com that default to short preambles.

Rumor has it that Intel is changing its tune and will go long on the preamble. For now, if youre running into incompatibilities, make sure that all your WLANs are running in the same mode, and if youre exposing your Wi-Fi to the public, set that preamble to long.