Think about a wireless LAN (WLAN) with enough throughput to match your switched Ethernet infrastructure.
That’s what the Institute of Electrical and Electronics Engineers (IEEE) is thinking about.
Last month, the international standards group launched a working group charged with crafting changes to the 802.11 WLAN standard so that these networks would deliver at least 100Mbps. That number is throughput – what users see when they transfer a file – 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. The 802.11a and 802.11g hardware can give users about 18Mbps to 22Mbps. The data rate for both is 54Mbps.
Silicon makers have boosted WLAN throughput to about 100Mbps. 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 Communications Inc., the first vendor with a 54Mbps 802.11a chipset, markets complementary metal oxide semiconductor 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, as it’s called in IEEE terms. “The greatest challenge will be to deliver higher performance while reducing power and cost,” says Craig Barratt, Atheros president and chief executive officer.
A reason to embrace wireless technologies is that high-throughput WLANs will eliminate cabling costs. That’s only true of the wires needed to connect clients to wiring closets. WLAN access points need to link via Ethernet cable to wiring closet switches.
Network executives already seem to be discounting high-throughput claims that are based on their WLAN experience. “Unless you are sitting right under the access point, you just don’t get the maximum throughput,” says Dewitt Latimer, deputy chief information officer and chief technology officer at the University of Notre Dame in South Bend, Ind.
WLAN throughput falls off 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 almost every case today, an access point is a shared medium: whatever throughput it can deliver is divvied up among the users connected to that 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. I don’t think high-throughput WLANs will be a big driver until we see things like streaming media applications being untethered,” he says.
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 will be used. In turn, these become the basis for evaluating and comparing what’s expected to be several technologies contributed by different vendors, according to Brian Mathews, publicity chair for the IEEE 802.11 Work Group that oversees this standards work.
