By Andrew Garcia  |  Posted 2006-07-23 Print this article Print

Backward Compatibility

Because products based on the 802.11n draft—or 802.11n itself, for that matter—will likely be used in conjunction with 802.11g devices, we tested the backward compatibility of the draft 802.11n routers and access points with WiFi-certified 802.11g-compliant products.
We tested each draft 802.11n router in conjunction with the Intel Pro/Wireless 3945ABG adapter included in our test Lenovo Group ThinkPad T60s and tested each draft 802.11n client adapter with a Cisco Aironet 1200 access point. In each case, we tested for maximum throughput, distance performance and compatibility with encryption.

Click here to read a review of Belkins draft 802.11n products. When used together with 802.11g access points, draft 802.11n client adapters provide undeniably improved performance at longer distances to the legacy devices. In our tests at 95 feet, the Cisco access point with the Intel adapter could muster only about 3.3M-bps throughput. Using the various draft 802.11n adapters with the Cisco access point at the same distance, we saw three to five times better performance. The Linksys Wireless-N Adapter tallied the lowest result at this range, at 9.5M bps, while the Belkin N1 Notebook Card pulled in more than 15M bps (with the Buffalo and Netgear cards in between).

We also saw glimpses of range improvements for 802.11g clients when using a draft 802.11n router, but we also encountered more interoperability problems: When we used the Intel adapter and the routers from Linksys, Buffalo and Netgear, we experienced unexpectedly limited bandwidth under certain circumstances—about 6M bps when we expected about 22M bps.

We determined that this problem is due to Centrinos incompatibilities with the way Broadcom implements the standard narrow 20MHz channel that 802.11b/g products use within the wide 802.11n 40MHz channel. With both Broadcom routers, we could choose whether to locate the narrow channel high or low within the wide channel. (If we set the wide channel to 7, the narrow channel could be either 5 or 9.) We determined that backward compatibility with the Centrino client suffered when we set the narrow channel to the high position, so our published interoperability numbers are with the narrow channel set low.

Both the Belkin and Netgear products advertise the narrow channel on the same channel number as the wide channel, so we cant explain Netgears poor performance in this scenario. Were still looking into it.

Some of the first products based on 802.11n show the wireless standards performance potential—and problems. Click here to read more. Representatives of D-Link, whose draft 802.11n products we expect to start reviewing in a few weeks, told eWeek Labs they encountered a similar problem in their own lab when using an Intel adapter with their Atheros-based router. They said they resolved the problem by upgrading to the latest Centrino drivers, but a check revealed that we were already using the latest drivers (Version, according to the Intel and Lenovo Web sites).

This channel problem may be specific to the Centrino adapter, as we could not duplicate the issue when using a D-Link DWL-650 802.11g adapter. For the time being, well say that mileage will vary—a lot.

More Data, More Security

Now armed with at least the potential to wirelessly transmit large chunks of data in a short time, we wanted to verify the ability of the devices under test to encrypt this data.

We secured each wireless session using WPA2 (Wi-Fi Protected Access 2) with AES (Advanced Encryption Standard) encryption. We tested each product pair at the same distances as we did in our throughput tests, but, because we were concerned primarily with high-speed results, weve published only the scores at 40 feet (see "AES-encrypted throughput" chart, Page 33).

The pair of Netgear products suffered most from encryption, falling a whopping 23 percent from their lofty unencrypted performance (but achieving a still-impressive 97.8M bps). The Belkin pair dropped about 14 percent with encryption, to 79M bps, while the Linksys scores remained about the same.

The Buffalo pairs performance actually improved slightly. However, the lack of full support for WPA2 marred Buffalos scores, so we tested Buffalos products with WPA using AES. (AES was an optional component of the original WPA spec, although Temporal Key Integrity Protocol, or TKIP, is the primary encryption algorithm.)

WPA2 is not a selectable option on the Buffalo Nfiniti Router, nor could we successfully complete a connection to a WPA2-protected network from the Nfiniti Adapter when using Buffalos Client Manager 3 wireless configuration tool. We could sometimes connect to a WPA2-protected network when we used the Windows XP supplicant (with the WPA2 patch installed), but we found this capability inconsistent from network to network, and it should not be trusted to work in the field.

At first, we could not get encryption to work at all with the Belkin N1 Wireless Router. In conversations with Belkin representatives, we learned that the N1 implementation does have a known bug: When the router is set to support both AES and TKIP, the client does not recognize that the network requires encryption and instead unsuccessfully attempts to associate unencrypted. However, this was not the problem in our tests. In the end, we needed to reinstall the router firmware to get encryption working properly.

Next Page: Frequent updates and revisions from vendors are expected during the next few months.

Andrew cut his teeth as a systems administrator at the University of California, learning the ins and outs of server migration, Windows desktop management, Unix and Novell administration. After a tour of duty as a team leader for PC Magazine's Labs, Andrew turned to system integration - providing network, server, and desktop consulting services for small businesses throughout the Bay Area. With eWEEK Labs since 2003, Andrew concentrates on wireless networking technologies while moonlighting with Microsoft Windows, mobile devices and management, and unified communications. He produces product reviews, technology analysis and opinion pieces for, eWEEK magazine, and the Labs' Release Notes blog. Follow Andrew on Twitter at andrewrgarcia, or reach him by email at

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