Apples AirPort Extreme Exploits 802.11ns Dual-Band Feature
Apples AirPort Extreme Exploits 802.11ns Dual-Band Feature
One of the benefits of 802.11n is that it supports both the 2.4GHz and 5GHz radio bands. However, up until now, routers based on the still-in-draft 802.11n spec have not leveraged this capability. Apple is leading the charge to change all that with its Airport Extreme, the first draft 802.11n-compliant wireless router eWEEK Labs has tested that supports both wireless radio bands.
Apples AirPort Extreme exemplifies some of the performance benefits of 802.11ns dual-band capability, but it also highlights many of the new questions that wireless administrators must learn to ask as they evaluate the technology. The Airport Extreme is among the first draft-802.11n routers to utilize both the 2.4GHz and 5GHz bands, maintaining backward compatibility with both 802.11b/g and 802.11a.
In the last few months, weve seen numerous laptops with integrated draft-802.11n that support both bands (including the Lenovo T60p and Apple MacBook with which we conducted the tests for this report). To keep prices down, however, most wireless router manufacturers up until now have forsaken the 5GHz band, even though the wireless chip sets on which their products are based are capable of the feature.
In fact, along with the AirPort Extreme, the only other dual-band router weve heard of is the Buffalo Wireless-N Nfiniti Dual Band, which is in a different price league than the AirPort Extreme. At $179, the AirPort Extreme seems pricey for a wireless router, but not when you see the $299 price tag of Buffalos router.
That said, the Nfiniti N Dual Band has one big advantage over the AirPort Extreme: The Buffalo router supports both bands simultaneously. The AirPort Extreme, in contrast, has only a single radio, so we had to choose which band we wanted to support. An AirPort administrator configures the chosen band from the Airport console, and this choice is programmed in software on the radio. We have not tested the Nfiniti Dual Band, but Buffalo marketing materials claim it advertises both bands simultaneously to support different kinds of traffic concurrently.
Despite the AirPort Extremes relative shortcoming, we applaud Apples decision to support the 5GHz band. During tests of the AirPort Extreme, we found throughput performance to be significantly more stable in the higher band, due in no small part to the lower level of interference in the 5GHz band when compared with the vastly more crowded 2.4GHz band.
We also realized greater bi-directional throughout performance in the 5GHz band. In that band, our test MacBook topped out at 107M bps at close distances, while only achieving 90.5M bps in the same test run in the 2.4GHz band. Similarly, our Lenovo client performed about 22 percent worse at close distances in the 2.4GHz band than in the 5GHz band.
Interpreting the guidelines set forth by the 802.11n Task Group in its draft revision, Apple has not implemented channel bonding in the 2.4GHz band to help avoid interference with legacy wireless networks. This means that 2.4GHz-band 802.11n clients can use only 20MHz channels, while 5GHz clients can use a full 40GHz client. We could see this in each clients supplicant application: In 5GHz mode, each client would receive and transmit at the 300M bps link rate, while 2.4GHz clients could attach at only a maximum rate of 144M bps.
We also noted variable results in performance at longer distances in our tests. At 85 feet, the Lenovo clients performance dropped off 32 percent in the 5GHz band, compared to a 19 percent drop in the 2.4GHz band, while the MacBook dropped 7 percent in the 5GHz band, compared to a 28 percent fall in the 2.4 GHz band.
Although both of our client machines leveraged Atheros XSPAN draft-802.11n wireless chip sets (the same technology found in the AirPort Extreme router itself), we still noted a substantial performance discrepancy between clients. This indicates that, with the standards still in flux, consistent interoperability still remains a moving targeteven within the same chip-set family.
Next Page: Some buyer bewares.
Some Buyer Bewares
However, despite the clients performance differences, we were pleased with the overall consistency we saw. In last years interoperability tests, we noted very spiky and irregular performance for almost every client-router pairing we tested. In these most recent tests, we experienced the oppositeclean and consistent results in different runs of the same pairing.
While we are happy to see Apple leveraging 802.11ns dual-band capabilities, the companys marketing materials illustrate the need for caution when evaluating dual-band technology.
In our initial discussions about the AirPort Extreme, Apple officials said the equipment could boost throughput performance by five times and double range performance compared to Apples previous-generation 802.11g technology. But further prodding revealed that the performance claims were for the 5GHz band, while the range tests were done in the 2.4GHz band.
As companies and home users start to look more seriously at 802.11n-based gear in the next two years, purchasers must remember to evaluate and judge a products claims against how the network will be deployed.
Also, administrators should get acquainted with all the antenna options that come with these new MIMO (multiple input/multiple output)-based products. Most devices weve seen have three antennae, but buyers must check to see if all three antennae are for both receive and transmit (3x3) or two transmit with three receive (2x3).
AirPort Extreme uncovered
Keeping appearances simple and elegant, the Airport Extreme is housed in a stark white chassis measuring 6.5 inches along each side and only 1.3 inches thick. All antennae are integrated inside the deviceone on each side of the front panel and a third on the back right corner. We found that the unit provided the best throughput performance if we aimed that corner in the direction from which we would be taking measurements, but the antenna placement provided good coverage in all directions.
The AirPort Extreme includes a three-port 10/100 switch with a fourth port for a WAN connection. The unit also includes a USB, with which we could connect either a network printer or a USB storage device over the network.
We configured the AirPort Extreme using AirPort Utility 5.0, which can be installed on systems based on either Microsoft Windows or Mac OS X. We found the retooled AirPort Utility to be a significant improvement over past versions, offering better interaction with the actual device for logging functionality, while maintaining the ease-of-configuration management profile. The new version supports legacy Apple wireless gear as well.
AirPort Utility offers a simple wizard to get the AirPort Extremes basic features up and working quickly, but we found much greater flexibility when managing the device in Manual Mode. In this mode, we could define which band we wished to support and whether we wanted to support legacy wireless clients, and we could choose from many wireless security features. WPA and WPA2 are both supported, in both the PSK and Enterprise flavors, as is WEP.
The AirPort Extreme can be turned into a NAS storage device via the integrated USB port, but this feature still needs workat least for Windows clients. The attached storage device must be formatted in Mac OS File System or in FAT32. Mac clients could see any of the disks we attached to the AirPort Extreme (as long as it was formatted on a Mac), but Windows clients could only access the disk if we formatted it in FAT32 on a Mac.
If we formatted the disk on a Windows XP workstation, the AirPort Extreme could not discover the volume. (We were testing with USB flash drives rather than external hard drives, so Apple officials are investigating if the AirPort Extreme was handling flash drives differently than external hard drives.)
The AirPort Extreme advertises the attached storage volume via AFP and SMB, but the easiest way by far to find the storage is to install the AirPort Disk Agent on either Windows XP or Mac OS X. The agent uses Apples Bonjour protocol to discover and advertise networking elements, so an AirPort Extreme-enabled drive instantly showed up in our Disk Agent, where we could access it simply by entering a password.
However, the Bonjour protocol relies on multicast traffic, something that many wireless clients do not handle well. For example, our Lenovo client could never locate the AirPort Extremes volume via Bonjour, nor could we manage the Airport Extreme (with the AirPort Utility) from the Lenovo system because we could never discover the router to manage it.
Technical Analyst Andrew Garcia can be reached at firstname.lastname@example.org.
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