802.11n tests show 'unbelievable' results at college

802.11n tests show 'unbelievable' results at college

Prototype Draft 802.11n wireless gear is exceeding expectations

The IT staff at Morrisville State College, where the first large-scale Draft 802.11n wireless LAN is being designed, says the prototype gear exceeds expectations.

The New York college, near the state's rural center, is in the final stage of building a pervasive campuswide WLAN based initially on Meru Networks' existing 802.11a/b/g access points. Those will start to be replaced this month and next with the newest Meru access points, which have a chipset that supports 11n. The first ten of these were shipped to the college last week.

With 11n, users can expect to see throughput of 100M to 300Mbps, depending on how the access point and client adapter are configured. That compares with 20M to 25Mbps today for 11a and 11g WLANs. In addition, users can expect to see high throughput sustained over longer distances from 11n access points. In tests that began in June, Morrisville network administrators are finding that 11n is delivering on its promise.

"Some of the statistics [from the tests] were just unbelievable," says Jean Boland, vice president of technology services for the college, in Morrisville, N.Y. "[In general,] speeds were five times that of 11g." Often, they were higher: According to Boland, a 50MB file uploaded from a laptop to a network drive took 3 minutes, 51 seconds with an 11g connection, but 26 seconds with an 11n connection -- nearly nine times faster.

An 11n chipset built into a new notebook PC transferred the same file in 8 seconds. That specific result was so startling, the testers thought they had made a mistake and ran the test again, with the same result.

The tests use Meru's prototype 11n access points. The clients are existing laptops fitted with a 2.4GHz 11n Linksys USB adapter, and new Lenovo T61 Thinkpad notebook PCs with a built-in Atheros Communications 11n chipset that can run on the 2.4GHz and 5GHz frequencies.

WLAN distance differences

Morrisville Network Administrator Matt Barber runs the tests in dorms and student rooms, and near active areas where other access points and equipment operate. His team sets up the access point and clients, and each time runs through an identical set of data transfers, using different kinds of files, at specified distances from the access point, so the results can be compared.

As with 11a/b/g, the 11n connection speed drops as distance to the access point increases -- but not as much. "We're losing a lot less of the speed as we move further away, compared to the effect we see in 11g," Barber says.

In addition, the 11n data rate decreases in much smaller increments. The 802.11 standard specifies that data rates decrease by set amounts at certain distances, like steps. "11n has similar behavior, but it has many more steps," Barber says. When clients are very close to the access point, the testers routinely record a rate of 280M to 300Mbps. Moving further away in stages causes the rate to drop to 240M to 279Mbps. "In some places, this is faster than if I plugged into the wall [Ethernet jack]," Barber says.

For Morrisville, raw distance is less important than penetration -- how well 11n can get through the cinder block and steel that are found in many of the campus' 45-odd buildings. Again, 11n is paying off. "We're seeing this [penetration] more than we expected," Barber says.

"You might see with your laptop a dozen [11n] access points, though only two to three might be visible to your eyes," Boland says..

The greater rate at greater distance means that Morrisville may be able to deploy slightly fewer 11n access points when the network is fully converted to 11n later this fall. The main benefit, however, Boland says, is that the dense packing of 11n access points and the greater reach of 11n clients means that users will be more likely to find and keep a high-throughput connection.

"We're designing the net so that we have lots of access points," Boland says. "As you move further, another access point will be in range to keep that [data] rate up high."

Tests will continue. The next priority is to find 5GHz 11n client adapters, either cards or USB devices.

So far, site surveys have been done in most campus buildings -- and conventional Meru 11a/b/g access points deployed in about 30 -- by IBM, which is the network integrator for the project. The remaining buildings will be done in August, so that returning students will be able to access the upgraded campus WLAN.

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