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Wireless LAN access points

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802.11n gear 10 times faster than current Wi-Fi offerings

Throughput tops 250Mbps in groundbreaking test; Bluesocket wins

By , Network World
October 27, 2008 12:07 AM ET

Network World - Testing 802.11n wireless LAN gear for enterprises means thinking big.

With the latest version of Wi-Fi promising vastly higher data rates compared with previous incarnations, a couple of laptops running a few FTP sessions through a single access point won't do.

Instead, Network World set up the largest public 802.11n test ever conducted. We invited all enterprise Wi-Fi vendors to supply not one but eight 802.11n access points, along with controllers if needed. Working with test instrument vendor VeriWave, we crafted test traffic from hundreds (and in some cases thousands) of virtual clients to see just how high the new 802.11n systems would scale, both in pure 802.11n settings and also with a mix of 802.11n and legacy clients. In all these tests, the goal was to determine 802.11n performance in an enterprise context.

Four vendors took us up on the challenge: Aerohive, Bluesocket, Motorola and Siemens. Some big names declined to take part, leaving us to wonder how ready their 802.11n offerings actually are (see "Big players missing in action"). We stand at the ready to test these products against our existing methodology, should they become comfortable enough to place their gear in a public test.

The vendors that did participate proved the adage that 90% of life is about showing up. Multiple vendors cracked the 2-Gbps mark in pure 802.11n throughput tests, pushing data rates of 250Mbps or more per access point. That's around a 10fold improvement in throughput over existing 802.11g and 802.11a access points, which makes a compelling case for considering 802.11n as a real alternative to wired connectivity to the enterprise.

Power is a big concern with the new systems, especially because some may need more juice than standards-based power-over-Ethernet (PoE) switches can supply. Some systems stayed within the limits of current PoE specs, while others may require upgrades to larger power supplies.

The new systems also showed rough spots in a few places. We couldn't complete throughput tests in some cases because access points became unresponsive or even rebooted. That's especially interesting given that all systems tested are built around the same Atheros radio module. The very different results speak to the different optimizations each vendor has done in working with the Atheros radios.

In the end, Bluesocket's BlueSecure access points offers the best combination of performance, power efficiency and features. Bluesocket's system wasn't the fastest we tested, but it exhibited consistently low latency and jitter, and it didn't suffer from some of the software bugs that hampered testing of other systems.

Each of the other systems had their own merits: Siemens' HiPath access points are extremely efficient with power, while Aerohive Networks' HiveAP offers an innovative alternative to controller-based designs and very high throughput. Motorola's new AP-7131 is still a work in progress and needs further software tweaks, but it too offers a unique design that soon will support up to three radios on the same access point, which will enable enterprises to use Wi-Fi and WiMAX on the same access point.

802.11n throughput and latency

We assessed all systems in terms of pure 802.11n performance; mixed-mode performance handling both 802.11n and legacy 11a and 11g clients; performance with a mix of common enterprise application types (our "WiMix" test, in which wireless clients handle a mixture of different frame sizes; power consumption; and system features.

"How fast will it go?" is understandably the first question when it comes to assessing 802.11n technology. We sought to answer that question by measuring throughput across eight access points, each moving traffic between 20 wired and 20 802.11n wireless clients (see "How we did it".

In these tests, access points used only 5-GHz radios; in later tests described below, we turned on both 2.4- and 5-GHz radios and used a mix of 802.11n and non-802.11n clients. For now, though, the focus was on pure 802.11n throughput and latency.

Using the VeriWave WaveTest WT-90 traffic generator/analyzer, we pounded each set of devices with short, midsize and large frames (in separate tests) to find the highest rate where the access points forwarded all traffic without loss – the throughput rate.

One significant finding is that traffic direction matters. In separate tests with frames moving downstream from (gigabit Ethernet to wireless clients), upstream and bi-directionally, throughput rates varied widely.

In the downstream tests, Siemens' access points moved large frames the fastest among all systems. Overall system throughput was greater than 2Gbps, or nearly 259Mbps on each of eight access points. Overall system throughput for the other three vendors' access points when handling large frames was between 1.89G and 1.94Gbps.

Upstream traffic generally achieved the highest rates. The Aerohive access points came out tops in the 802.11n upstream tests, moving traffic fastest for all three frame sizes. In fact, the HiveAP 340s' throughput for large frames headed upstream – 2.109Gbps, or nearly 264Mbps per access point – was the fastest data rate we recorded in the entire test.

These results are good news for all vendors: Even the slowest result is dramatically higher than the roughly 25Mbps per access point available from current 802.11g or 802.11a products. In the best case, throughput is better than 10 times higher with enterprise-grade 802.11n gear.

While access points generally moved large frames close to the theoretical maximum rates in the downstream and upstream tests, it was a different story with bidirectional traffic. Aerohive's access points were fastest by far, moving large frames bidirectionally around 2.7 times faster than the slowest access points (from Siemens).

But the top rate bidirectionally, even for the Aerohive access points, was only around 70% as fast as its upstream-only rate. Limitations in internal bus capacity, direct memory access transfer capacity and memory optimization may explain the difference in rates.

So far we've concentrated on large-frame testing, which generally produces the highest rates. Throughput differences for short and mid-length frames were more pronounced than with large frames; in some cases we weren't even able to complete throughput testing.

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