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802.11 interoperability and compliance

Feb 08, 20063 mins
Cellular NetworksNetwork SecurityWi-Fi

* What is Wi-Fi ‘backward compatibility?’

The last newsletter discussed interoperability among various flavors of 802.11 networks, including forthcoming high-speed 802.11n networks.

I’d like to point out a few clarifications about “backward compatibility” among networks, a trait that is partly semantics and partly technology. In addition, since most 802.11n networks will make use of the 5-GHz band, how will that affect 802.11n deployments worldwide, given that different countries have different rules about using that spectrum?

First, note that the vendor community considers today’s dual-band, multimode equipment (gear supporting two radios and 802.11a/b/g in one device) to be backward-compatible with other dual-band, multimode equipment. The reasoning is that 11a clients can find a match to an 11a radio, and 802.11g clients can find a match to an 802.11g radio. But the compatibility, of course, doesn’t cross bands; in other words, 802.11a doesn’t suddenly become compatible with 802.11g just because the gear supports multiple network types in a single device.

Meanwhile, you likely know that 802.11g is somewhat backward-compatible with 802.11b in that disparate clients and access points will discover one another and communicate. In most cases, however, you’ll be running an 11b network at 11b’s lower speeds once an 11b client joins the 11g network. A possible exception is Meru Networks’ Wi-Fi architecture; Meru designed its own media-access control (MAC) chip to achieve a logical separation between 11b and 11g transmissions. (See story, “Meru claims peaceful 802.11b/g coexistence”).

In terms of international compliance, you’ll be facing the same issues that you do today with 802.11a. If you are using a WLAN system built from Atheros chips, your system will be able to “tune” to the parts of the 5-GHz band that are allowable for Wi-Fi use in the various countries. Depending on who your systems provider is, you may or may not have to configure your access points on a per-country basis yourself. Many WLAN system vendors using Atheros chips support different SKU numbers for different geographies. The appropriate configuration for each country is stored in FLASH or EEPROM and is configured for the country based on SKU during manufacturing, according to Atheros.

You’ll need to check, however; smaller vendors using Atheros chips, such as Trapeze Networks, offer 5-GHz products under a single SKU, and leave it to the IT manager to handle the per-country configuration.

Products might all be shipped to one enterprise site, where configuration for each country might be done then shipped out again to the various countries from there. Or they can be shipped to various geographies directly and be configured locally.

As clients roam between regions, the 802.11 standard enables appropriate tuning between client and AP. An 802.11d beacon scans the airwaves for the AP’s configuration and communicates with the AP using the appropriate frequency.