Wireless LAN throughput on the rise

Think about a wireless local area network (WLAN) with enough throughput to match your switched Ethernet infrastructure. That’s what the Institute of Electrical and Electronics Engineers (IEEE) is thinking about.

The international standards group has launched a working group charged with crafting changes to the 802.11 WLAN standard to make these networks deliver at least 100Mbps. That number is throughput, what users see when they transfer a file, for example, as distinct from the data rate, which is the raw speed before you subtract the overhead associated with the protocol.

In the case of 802.11, the overhead adds up to a whole lot, typically more than half of the data rate. An 802.11b access point, rated at 11Mbps, typically gives a throughput of less than 6Mbps, often far less. The 802.11a and 802.11g hardware gives users about 18M to 22Mbps. The data rate for both is 54Mbps.

Silicon makers have been boosting WLAN throughput to around 100Mbps for some time. The catch is that you have to have the same chips in both the client and the access point, and high throughput sacrifices conformity to the 802.11 specification. Atheros, the first vendor with a 54Mbps 11a chipset, markets complementary metal oxide semiconductor (CMOS) chips that support what it calls ‘Super G’ and ‘Super A/G’ — proprietary boosts of up to 100Mbps throughput.

Atheros plans to contribute these and other technologies to the 802.11n task group. “The greatest challenge will be to deliver higher performance while simultaneously reducing power and cost,” Atheros president and chief executive officer, Craig Barratt, said.

He said 802.11n would “promote the idea that wired networks can be replaced with wireless technologies”.

One reason to embrace them was that high-throughput WLANs would eliminate cabling costs. But that’s only true of the wires needed to connect clients to the wiring closets. WLAN access points still need to link via Ethernet cable to wiring closet switches.

WLAN throughput falls off more rapidly the farther a client device moves from an access point. The drop depends on how much metal, wood, concrete and other construction materials are between the two devices. In addition, in almost every case today, an access point is a shared medium: whatever throughput it can deliver is divvied up among however many users connect to that one access point.

“Most practical applications, such as three students sitting under a tree working on a paper (with wireless notebooks), tend to be insensitive to bandwidth,” Barratt said. “I don’t think high throughput WLANs will be a big driver until we see things like streaming media applications being untethered.”

The 802.11n task group’s first order of business will be to define a group of application scenarios, describing how the high-throughput technology would be used.

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