Navigating the Shifting 802.11 Sands

Dual-mode APs like Cisco's Aironet 1200 are an oasis of interoperability for companies traversing uncertain wireless terrain.

January 27, 2003

22 Min Read
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Organizations that want to upgrade their existing 802.11b infrastructures will need to maintain backward compatibility; few can justify trashing their 802.11b equipment in favor of new 802.11a products. One option is to overlay single-mode 802.11a access points on the current 11b wireless network, but that setup can be unwieldy and expensive. Dual-mode APs, on the other hand, are easier to manage and cost far less than doubling up 802.11a and 802.11b APs.

You can simplify new installations of any kind that require 11a/11b coverage--SOHO, enterprise or hot-spot settings--by using dual-mode APs.. For example, organizations that don't have WLANs (wireless LANs) may want to provide hot zones to cover conference rooms or cafeterias; a dual AP is ideal for this scenario. In addition, some of the devices tested add value by providing upgrade paths to 802.11g and beyond (see "802.11g Adds to the Mix").

Of course, there's a catch: The propagation characteristics are vastly different among radios, and, save for a few of the APs we tested, 802.11b coverage is far greater than that of 802.11a. In a dual-AP environment, proper design of 802.11b cells would leave large dead zones between 802.11a cells. This can be fixed by lowering the output power of the 802.11b radio, if the AP allows, so that the coverage areas are concentric, or by supplementing the patchy 802.11a network with single-mode 11a APs. Either way, this problem affects every dual-mode infrastructure and, while it will require time and money to solve, the cost for doing so is usually less than that of overlaying 11b and 11a devices.

Another big concern for wireless network administrators is security. Unfortunately, none of the APs we tested offers a groundbreaking solution.

Although WEP (Wired Equivalent Privacy) is a good basic security precaution because it's easy to implement and doesn't cause a performance hit, WEP's days are numbered. Most vendors promised that WEP's pending successor, WPA (Wi-Fi Protected Access, see an overview), will be supported through free firmware upgrades, but only Cisco provides a stand-in for the moribund WEP--TKIP (Temporal Key Integrity Protocol).Finally, as in any wireless deployment, management is key. Most of the products we tested support SNMP--a step in the right direction. Enterprises with large installations of dual-mode APs will find Intermec's and Cisco's devices enticing because they offer central management suites that can be purchased separately.

With these issues in mind, we gave Cisco's Aironet 1200 AP our Editor's Choice award despite it being the priciest AP we tested: At $1,399, it's more than five times the cost of the least-expensive unit. In its favor, the 1200 offers an excellent mix of performance, range, ease of configuration and installation, and management options. Linksys' WAP51AB snagged our Best Value award because it held its own against rival APs in range and performance, all for just $279.Cisco's Aironet 1200 Series AP, true to its Aironet heritage, delivers superior performance, impressive range and a strong feature set to give administrators plenty of control over their networks' wireless segments. We tested the 1200 configured with dual 802.11b and 802.11a capabilities; it's also available in single 802.11b and 802.11a builds.

Encased in a sturdy cast-aluminum shell, the 1200 features mounting brackets that accommodate almost any installation. This coupled with the 1200's plenum-rating and support for PoE (Power over Ethernet) mean the device can be installed in nearly any location. Clearly overengineered to meet future needs, the 1200 is based on a modular radio design that will stave off obsolescence by letting future radio chipsets, like the upcoming 802.11g standard, be incorporated via field upgrades.

The 1200's 802.11b capabilities are handled by an internal mini-PCI card. Once the standards have been finalized, this module will be supplanted by an 802.11g-capable card, Cisco says. As for 802.11a, the 1200 was the only AP we tested that didn't incorporate the ubiquitous Atheros chipset. Instead the 11a module, developed in-house by Cisco through its acquisition of Radiata, is a PCMCIA card with an attached paddle antenna capable of both omni- and directional-patch configurations. Marrying the antenna to the radio complicates the installation somewhat, but that's a requirement for FCC certification of 5-GHz products that make use of the lower four nonoverlapping channels. To thwart thieves, the module can be padlocked to the AP, though nothing keeps passersby from altering its omni or patch orientation, which could prove to be a headache.

We got the 1200 running quickly. After connecting to our test network, the 1200 grabbed an IP address from our DHCP server. We could then access the device from any PC on our network. Cisco offers an impressive range of functionality via the 1200's Web-based management interface, though we found it somewhat cluttered and difficult to navigate. Managing to sidestep a shortcoming of many dual-mode APs, Cisco nicely integrated options for both radios into its configuration pages.The 1200 supports SNMP, is compatible with Cisco's CiscoWorks network management tool and has enough horsepower to migrate to the company's IOS in the future, a plus for environments with Cisco switching/ routing infrastructures.

Performanceclick to enlarge

As for performance, the 1200 led the pack. At just more than 6 Mbps, Cisco's 802.11b throughput beat rivals by a margin of 1 Mbps or more, and at just shy of 24 Mbps, the 1200 came out on top in 802.11a mode as well. Total aggregate throughput of tests with 802.11b and 802.11a clients running simultaneously reached 28 Mbps, proving that the AP could easily handle the traffic load of both radio spectrums concurrently.

In range testing, however, the 1200 lost a little ground. The device's range for the 802.11b module was greater than that of the other units tested, but 802.11a range lagged behind that of the Proxim, Intermec and Linksys boxes. We were able to squeeze a 20 percent increase in 802.11a range in the direction the AP was pointed by changing the paddle antenna's orientation from omni to patch. Of course, in omni mode the signal is propagated in all directions; patch mode focuses it in one direction only, leaving all other areas uncovered.

The 1200 is ahead of the curve when it comes to security. As expected, the unit supports 128-bit WEP keying and 802.1x authentication, as well as Cisco's proprietary LEAP (the company's version of the Extensible Authentication Protocol). In addition, as a replacement for WEP, Cisco offers the more robust and dynamic TKIP.

Aironet 1200 Series Dual AP, $1,399. Cisco Systems, (408) 526-4000, (800) 326-1941.

Proxim Orinoco AP-2000 Dual-Mode Access Point | Intermec MobileLAN WA22 | Intel 5000 LAN Dual AP | Linksys WAP51AB Dual-Band Access Point | D-Link DWL-6000 Air Pro Multimode Access Point

Proxim Orinoco AP-2000 Dual-Mode Access Point

Despite average 802.11b performance, Proxim's Orinoco AP-2000 Dual-Mode AP pleased us with its good marks for 802.11a throughput and excellent coverage with the same radio. We were also impressed with its breadth of enterprise-oriented management features.We were not thrilled, however, about the AP's design: It arrived in our labs in pieces (assembly required) for the relatively steep $895 price.

The AP-2000's modular physical design beneath a white plastic shell is clearly derived from Lucent's original Orinoco APs, now under Proxim's name. The device has two PCMCIA slots that we populated with a stand-alone Orinoco Gold 802.11b client card and a Proxim 802.11a card with an integrated attached antenna; the retail box we received came with only the 11a radio. We had to use our own 11b card.

Proxim did not confirm whether an upgrade to future wireless standards would be an option for the AP-2000, but the PC Card design would appear to conveniently accommodate future radios.

Installation was a breeze; we plugged the AP-2000 into our network and it immediately picked up an IP address from our DHCP server. We were then able to get into the unit's Web-based management interface to set a static IP address.

Noticeable is the AP's lack of range for its 802.11b module. Our range testing was done without an external antenna, and our poor results prompted Proxim to ask us to test with an external antenna. We did so, but our results did not change dramatically. In contrast, the AP-2000's 802.11a range led the pack.In testing throughput for each radio, the 802.11b's came to 4.6 Mbps, while we measured 802.11a's throughput at about 21 Mbps. When we tested both modules simultaneously, total aggregate performance amounted to a dismal 23 Mbps.

Still, this AP's versatility is impressive. It supports 802.11b bridging, which lets enterprises connect disparate wired networks where landlines cannot be run. And unique to the AP-2000 is wireless support for the 802.1q VLAN protocol. The device also offers an array of enhanced monitoring and diagnostic tools. These features make it a good fit for enterprises requiring a score of capabilities, and for demanding hot spot environments, but only if you can swing the price.

Orinoco AP-2000 Dual-Mode Access Point, $895. Proxim Corp., (408) 731-2700, (800) 229-1630.

Intermec MobileLAN WA22

Intermec, no stranger to the enterprise and industrial wireless scene, offers dual-mode coverage in its WA22 AP. The device, second only to Cisco's in price, proved very manageable in our tests, but we were disappointed with its range and performance.Setup was a joy with Intermec's MobileLAN access utility. We connected the AP to our test network and the utility let us easily assign the IP address. From that point we were able to connect from any network PC to the device's onboard Web-based management configuration pages. The WA22 also supports DHCP once a static address is set and you gain access to the device's Web-based management page. Management difficulties present in many large wireless deployments are alleviated with WA22 installations thanks to Intermec's MobileLAN Manager, an add-on Java-based administration tool.

The WA22 supports SNMP and boasts a feature set, including wireless bridging and load-balancing capabilities for the 802.11b radio, that should more than meet most enterprise needs.

Range results for the WA22 were a mixed bag. The 802.11a half ran neck-and-neck with Linksys and behind only Proxim, but, like D-Link's DWL-6000 and Proxim's Orinoco AP 2000, the 802.11b portion of the WA22 posted lesser range distances than did the 802.11a radio. The reason is difficult to pinpoint because the propagation characteristics of the 802.11b radio should allow for greater range than its 802.11a counterpart. Nonetheless, Intermec acknowledged that these results were in line with its testing. The company added that typical installations of WA22 use higher gain external 802.11b antennas and requested that we try testing the unit with separate Intermec dipole antennas. We tested with the extra antennas to simulate what Intermec says is a real-world installation of the WA22. Although the results were not included in our official range findings, the numbers improved drastically; with the new antennas, range results mirrored Linksys'.

The WA22 posted respectable results in our performance testing. The 802.11a radio came away with just short of 22 Mbps, while the 802.11b radios got 4.75 Mbps. With a total aggregate throughput of 26 Mbps, the WA22 can handle the load of both radios transmitting at the same time.

Intermec also includes a port for a 100-Mbps fiber-optic connection, which lets the unit be linked to a fiber network via an MT-RJ connector. The WA22 can receive power only via PoE. While this can make some deployments easier because AP placement can be decided without power-outlet considerations, Intermec's PoE injector is absurdly large. At roughly six times the size of Cisco's injector, Intermec's PoE block can create space issues, cluttering drop ceilings and wiring closets.As for security, beyond basic 128-bit WEP keying, Intermec has included support for 802.1x authentication.

MobileLAN WA22, $1,149. Intermec Technologies Corp., (800) 934-3163, (425) 348-2726.

Intel 5000 LAN Dual AP

Intel's 5000 LAN Dual AP is an 802.11a LAN AP populated with a mini-PCI 802.11b radio. In fact, similar to Cisco's design, Intel intends its 802.11a APs to be user-upgradeable to handle both 802.11a and 802.11b traffic. But because the upgrade process requires that end users open the device, Intel says the FCC has yet to sign off on the legality of such an upgrade kit. For now, administrators interested in dual-mode coverage will need to purchase 5000 LAN Dual APs rather than upgrade an existing Intel 802.11a installation. When we asked about 11g support, Intel neither confirmed nor denied, saying that if possible it will make the 5000 11g-upgradeable, but if not, another product will be released for both 11g and 11a.

Setting up the 5000 was a breeze. We connected directly to the unit via its factory-set static IP address to assign it a new one on our test network (DHCP support was lacking until we got a firmware upgrade). Any PC on our network could then access its Web-based management console.The 5000's management interface, while easily navigable, does a poor job integrating options for both radios. That, coupled with the fact that Intel offers no central management tools, means administration of larger wireless networks could be a hassle. On the plus side, the unit offers SNMP support.

Intel's AP fell significantly short of rivals in performance. With an average throughput of approximately 22 Mbps, 802.11a bandwidth wasn't too far behind, but performance for the 5000's 802.11b module was another story: We were disappointed with the device's 3.5-Mbps speed.

The 5000 fell in the middle of the pack in range testing. The unit trailed Proxim's, Intermec's, Linksys' and Cisco's devices in 802.11a range but fared a little better in our 802.11b tests. The 5000 boasts a software-configurable antenna that can be set to omni or patch configurations, but we saw little impact on coverage distance with the antenna in patch mode.

The 5000 supports up to 128-bit WEP keys and can be set up to work with a RADIUS server using 802.1x.

5000 LAN Dual AP, $649. Intel Corp., (800) 538-3373, (408) 765-8080. WAP51AB Dual-Band Access Point

We have mixed feelings about Linksys' WAP51AB AP. The device performed well but is significantly lacking in functionality, seeming better suited for home and small offices than for enterprise deployments. However, at the bargain price of $279, it earns our Best Value nod.

The AP's design mirrors that of other Linksys products, and we expected similarities in ease of setup as well. As anticipated, the installation and configuration process was hassle-free. We connected the AP to our test network and loaded the installation and configuration software on a machine on the same subnet. The installation software quickly discovered the AP and let us configure the IP address, subnet mask, AP name, SSID (service set ID), channel and WEP for both radio modules through a user-friendly interface. One caveat: Because the device cannot receive an address through DHCP, administrators must assign static addresses to all access points--a flaw that will be less noticeable in small deployments.

Considering that Linksys targets the WAP51AB at deployments up to 500 nodes, as well as the hot-spot market, we were surprised by its lack of functionality and features. In addition to the settings we were able to change through Linksys' installation and configuration wizard, the Web-based management interface only let us edit MAC address filters and a few rarely altered wireless settings, such as beacon intervals and RTS (request to send) threshold values. Considering the broad scope of the intended market, such a thin feature set will hamstring administrators who are interested in more than the most basic of wireless deployments.

On the positive side, though, both range and performance put the WAP51AP on par with higher-priced rivals. Our tests showed throughputs of about 20 Mbps for 802.11a and close to 4.5 Mbps for 802.11b. Testing both radios with simultaneous throughput tests, the total average aggregate performance was an acceptable 24 Mbps. We were even more surprised by the range results the Linksys dual AP posted: Second in both radio spectrums, the Linksys device was close behind Cisco in 802.11b and Proxim in 802.11a range.Linksys says that a firmware upgrade, due out soon, will offer several new features, including many enhanced security options.

WAP51AB Dual-Band Access Point, $279. Linksys Group, (949) 261-1288, (800) 546-5797.

D-Link DWL-6000 Air Pro Multimode Access Point

The DWL-6000 Access Point posted good performance stats, and with its low price--$299--it provides great value in terms of features and reliability for small installations. However, range issues and the lack of a robust feature set make it a poor choice for enterprise WLAN deployments.

Even though the AP has DHCP client functionality, the default configuration is set to a factory-default static IP, requiring us to connect directly to the device to add it to our test network. Save for a few products that do all basic setup through utilities, most APs with DHCP support are set by default to grab an address via DHCP. If a DHCP server isn't available or the feature doesn't work, the device can be communicated with via its static address. Having the two choices work in this order provides greater flexibility.In addition, we had difficulty initially logging into the Web-based management console because of a documentation error. The case-sensitive user name and password login kept us out until we determined that the manual incorrectly listed the user name as "admin" rather than "Admin." D-Link has confirmed this issue and promises to address the problem immediately. Otherwise, the AP was easy to configure; all settings could be established locally through the included AP manager software or remotely via the unit's Web interface.

Range was the DWL-6000's main deficiency--we found coverage for both the 802.11a and 802.11b radios almost identical. Although the argument can be made that concentric coverage areas can be a plus in deployment of dual-mode access points, the range was so weak that the D-link offering barely escaped being relegated to the lowest common coverage area of all access points. Overall, it landed dead last.

Performance tests, however, were a brighter spot. The DWL-6000's 802.11a clients showed throughputs of around 20 Mbps, while 802.11b tests posted about 4.5 Mbps averages--all-around respectable marks. We noticed a slight performance decrease when running tests with 802.11b and 802.11a clients concurrently, putting total aggregate throughput at a miserable 22 Mbps.

The DWL-6000 supports strong WEP keying to the tune of 256 bits for the 802.11b radio and 152 bits for 802.11a, though most non-D-Link client cards don't support WEP past 128-bits. Unfortunately the device doesn't support other security protocols.

DWL-6000 Air Pro Multimode Access Point, $299. D-Link Systems, (877) 453-5465. www.dlink.comJesse lindeman is a consultant and a research associate at the Center for Emerging Network Technologies at Syracuse University. He has been a systems administrator for a historic roofing firm in Washington. Write to him at [email protected].

julio caraballo is a technology manager for a Fortune 500 company in the Dominican Republic with more than seven years of IT experience. He is also a systems engineer and freelance writer, contributing a weekly section to Network Computing's Mobile Observer newsletter. Write to him at [email protected].

Ninety percent of 2001 WLAN shipments were 802.11b, but by 2007 more than two-thirds will be dual-band--802.11b or 802.11g and 802.11a, according to Gartner.

We'll buy that. After all, dual-mode APs offer the best of both worlds--11b's range with 11a's bandwidth, a match made in heaven. We evaluated six dual APs in our Syracuse University Real-World Labs®, from Cisco, D-Link, Intel, Intermec, Linksys and Proxim. All the devices tested supported both specs, and some had the bonus of an easy upgrade path to 802.11g.

We tested features, functionality, range and performance and, even after factoring in price, awarded Cisco's Aironet 1200 our Editor's Choice thanks largely to its all-around strong showing with enterprise needs in mind. At $1,399 the 1200 isn't cheap, but for demanding installations especially, cost is relative--you can pay more up front, or you can add APs later to compensate for poor range, poor throughput, and extra time spent compensating for lightweight management tools. For the more budget conscious, Linksys' WAP51AB, our Best Value award winner, lacked some bells and whistles but held its own against rival APs in range and performance, for the reasonable price of $279.We conducted feature, functionality, range and performance tests with each product in our Syracuse University Real-World Labs®. For throughput tests we used NetIQ's Chariot 4.3 network-performance application, using 1.2-GHz Toshiba Satellite notebook computers with 256 MB of RAM running Microsoft Windows XP as our mobile clients. For our base throughput tests, the laptops were located 5 feet from the AP, and the AP was connected to an isolated 100-Mbps Cisco switch in our lab. We used 100 iterations of 1-MB, TCP-based, unidirectional long-file receive transfers, our standard throughput test for wireless LANs.

We began by testing each mode, 11a and 11b, with one and two clients connected to the AP, and then both modes working concurrently with one client each. In each case we tested with and without 128-bit WEP (Wired Equivalent Privacy) enabled. Although testing with a limited number of stations does tend to provide best-case performance, it has the advantage of allowing comparisons to previous lab tests.

For our range tests, the APs were placed in a typical ceiling-level location in a large walled classroom/office building constructed in the mid-1980s (most walls are Sheetrock over metal studs, and most doors are metal). We ran a continuous ping from the laptops to the static IP address set up on the APs to measure range based on packet loss from various locations. Since we did not have physical access to all offices, our maps do not show all areas of coverage, but they do provide an accurate representation of product differences and maximum range that would be achieved in a typical building.The 802.11g standard is still in draft form, but understanding its impact on the WLAN scene is a must for wireless administrators. Some feel that 802.11a will be obsolesced quickly by the backward-compatible 802.11g, while others say 802.11a's positive traits heavily outweigh 802.11g's pros. The debate has begun and won't be settled soon. Here's a primer for administrators in need of high-performance WLAN technologies.

To put it plainly, the advantage 802.11g affords is an increase in speed while maintaining backward compatibility with 802.11b. Operating in the same 2.4-GHz spectrum as 802.11b, 802.11g uses the OFDM (Orthogonal Frequency Division Multiplexing) transmission type that 802.11a uses, while also supporting the DSSS (Direct-Sequence Spread-Spectrum) transmission type 802.11b uses. Combining these two transmission types lets 802.11b and 802.11g clients co-exist on the same wireless network while theoretically enabling 802.11g to reach speeds equal to 802.11a.

By using the same transmission type and modulation as 802.11a, while remaining in the 2.4-GHz spectrum, 802.11g carries some range and performance characteristics from both 802.11b and 802.11a. Although 802.11g is capable of a theoretical 54-Mbps throughput, it likely will not reach the same speeds as 802.11a (we've seen averages around 16.5 Mbps in prestandard products) because of 2.4-GHz interference problems and the longer resend intervals required for backward compatibility with 802.11b. On the plus side, ranges well above 802.11a (but decidedly less than 802.11b) are expected because of wave characteristics at the 2.4-GHz spectrum.

The choice to deploy 802.11g is also not nearly as cut and dried as some may think. Administrators with 802.11a experience know that external antennas are a nonoption for APs that harness all eight nonoverlapping channels (FCC limitations require attached antennas, fixed transmit powers and antenna-gain limits on APs that allow use of the lower four nonoverlapping channels). The choice to forgo some freedom in favor of all eight nonoverlapping channels is to administrators' advantage with 802.11a because deployment is greatly eased as more nonoverlapping channels become available. 802.11g, however, continues to use the same three nonoverlapping channels characteristic of 802.11b, perpetuating the deployment issues extant with those installations.

802.11g circumvents some of the FCC restrictions levied on 802.11a, letting administrators use auxiliary antennas and adjust transmit power. Also, because of 802.11g's compatibility with 802.11b, the same antenna equipment may be used from current 802.11b deployments.Those interested in supporting clients of both technologies should consider dual APs that, either off-the-shelf or through field upgrades, support both 802.11a and 802.11g, but choosing to deploy one or the other isn't as simple. While 802.11g's increased throughput and backward compatibility with 802.11b may be enticing, administrators interested in high-performance WLANs simply cannot ignore 802.11a's drastic difference in speed and the standard's five additional nonoverlapping channels. --Jesse Lindeman


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