Dual Band By Design

Outperforms Cisco

I tested the NIC's performance using NetIQ's Chariot 4.1 and a selection of 11a and 11b access points. For 11b throughput tests, I used Cisco Systems' 1200 series access point. I performed 100 iterations of 1-MB TCP file transfers (filesendl and filercvl) and was surprised by the transmit results of 6.3 Mbps and receive results of 6.1 Mbps. That's faster than Cisco's Aironet 350 cards, which we use as the performance standards for 11b NICs. Additionally, I found no significant degradation in throughput with WEP (Wired Equivalent Privacy) enabled.

To evaluate range, I installed the AP above a dropped ceiling in our test facility and ran a continuous ping test until the pings timed out. Even with multiple walls and steel-and-glass doors, the combo card working in 802.11b mode achieved a maximum range of about 170 feet--again comparable to that of the Cisco Aironet 350. Based on these tests, it looks like you won't have to sacrifice 11b performance with these NICs.

I used the Netgear HE102 802.11a AP, based on an earlier Atheros reference design, for range and performance tests of the card in the 802.11a-only mode. With the same setup used for 11b testing, the average transmit and receive throughput was approximately 22 Mbps. Again, performance degradation with WEP enabled was nominal. These results are slightly better than that of the Netgear HA501 802.11a card I tested in the lab. The maximum 11a range of the combo card in our environment was 115 feet. Atheros said range should improve once APs based on the AR5001X chipset are introduced, a development likely to occur by year's end.

On the Roam AgainA key selling point of dual-band cards is their ability to roam seamlessly between the 11a and 11b networks. To test roaming, I configured a Proxim Harmony 8570 802.11a AP and the Cisco AP1200 802.11b with identical SSIDs (service set IDs) and set the card to work in auto-wireless mode. I collocated the two APs above the dropped ceiling, and used the continuous ping test to check for the packets dropped and the time required to roam between the systems as I walked further and further from the APs.

As expected, the combo card associated with the Proxim AP provided the best available data rate. As I walked away from the APs, the data rate fell from 54 Mbps to 6 Mbps until maximum 11a range was reached. At this point the card lost association with the Proxim AP and started to scan for other available networks and dropped many packets. After a delay of 12 to 15 seconds, the card switched to the Cisco 802.11b AP. The card maintained its association with the 11b AP even as I walked back into range of the 11a AP. In fact, I had to force the card to associate to an 802.11a network and then force it to automode to reinitiate roaming. Netgear and Atheros told me this behavior is normal. Rather than incur the session disruption that would occur if it roamed back to the 11a AP, the system is designed to maintain connectivity with the 11b system.

Roaming will pose an issue for time-sensitive applications, but the basic functionality of this dual-mode NIC is impressive. For organizations taking a long-term approach to wireless, it's worth a little extra money to get dual-mode capabilities in a single card--and you don't have to sacrifice performance.

Alireza Dehghanpur is a research associate at the Center for Emerging Network Technologies at Syracuse University. Write to him at [email protected].