Many companies devote considerable attention to purchasing Wi-Fi access points, routers, and switches, giving far less thought to Wi-Fi client selection. But it takes two to tango: client devices have major impact on WLAN operation. Supporting a hodge-podge of Wi-Fi clients complicates maintenance, trouble-shooting and performance / security planning. Standardizing on a few well-chosen Wi-Fi clients can make a big difference.

Embedded or after-market

One reason for client diversity is embedded wireless. From laptops and PDAs to VoIP phones and wireless scanners, many products now ship with Wi-Fi on-board.

In some cases, Wi-Fi options are limited. Criteria like compatibility with upstream systems (e.g., VoIP call servers, factory automation servers, point-of-sale systems, patient care systems) may drive client device selection process. Not that you should ignore Wi-Fi capabilities when selecting such products -- you simply may have no choice between embedded and after-market adapters.

Most enterprise WLAN devices can be used with or without embedded wireless. Buying laptops, tablet PCs, and PDAs with embedded Wi-Fi is convenient for the user, and there are no PC cards or USB fobs to forget, lose, or break. Purchasing (or renting) a fleet of laptops with an embedded Wi-Fi mini-PCI adapter also promotes consistency, at least across those devices acquired at a given point in time.

But embedded offerings change over

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time. Ultimately, you may be forced to support several generations of embedded mini-PCI clients. If your workforce requires multiple operating systems (or versions thereof), it may be impossible to use the same embedded client for all. After-market client devices provide platform-independence: you can upgrade everyone, without regard to which laptop model they're currently using.

OS and interface must also be considered when choosing an after-market Wi-Fi client. There are many 16-bit 802.11b PC cards, but 802.11a/g PC cards typically require 32-bit PCMCIA slots and cannot be used in laptops where one of two slots is already occupied, or in PDAs with 16-bit PCMCIA "sleds." USB adapters may sound like a good idea for desktop PCs, but USB 1.x interfaces limit throughput, especially for 802.11a/g. Interface conversion can promote uniformity -- for example, adding PCMCIA-to-PCI adapters to desktops so that that same wireless PC card can be used in all desktops and laptops.

Comparing Wi-Fi clients

Beyond form factor, there's much to consider when selecting a Wi-Fi client. You might assume that every wireless Dell laptop is the pretty much the same, or that Intel Centrino performance is equivalent no matter which laptop you buy. But in a February 2006 lab test, Dave Molta and James Blandford found noteworthy differences between mini-PCI adapters used in Dell, Lenovo, HP, and Toshiba laptops.

Their report, "Radio-Tested WLAN Clients," documents 802.11g and 802.11a signal strength (rate vs. range) and throughput. Benchmark tests, conducted in lab isolation and office environments, illustrate the impact of factors like antenna technology and internal packaging (radio isolation). Some differences were modest -- for example, 3 of 4 Centrinos achieved similar 802.11g real-world throughput. Other differences were more striking -- for example, data rates dropped twice as fast at a distance in Broadcom 802.11a adapters. Click here to view these detailed test results.

Molta and Blandford also measured battery life, finding that power consumed during Wi-Fi use was consistently lower than that consumed by Ethernet. And, while readers may be tempted to compare the duration achieved by each laptop (ranging from 250-350 minutes), the authors caution that battery size and weight have a more significant impact on this metric than differences in radio circuitry.

Finally, this report compares client software delivered with each tested laptop, noting broad support for 802.1X EAP types, as well as differences between connection manager look-and-feel and IT administration features like configuration import and locking.

Note that this study compared just a few Wi-Fi clients -- albeit a very relevant subset, representing 75% of the business laptop market. But the factors compared in this study, and the author's benchmark methodology, make excellent reading no matter which kind of Wi-Fi client you're considering.

In the future, IEEE 802.11T may help consumers compare such metrics. These "Recommended Practices for Evaluation of 802.11 Wireless Performance" will make it possible to test 802.11 devices using industry-recognized test metrics, methodologies, and environments. In particular, 802.11T will make it easier to compare independently-tested metrics like throughput, path loss, receiver sensitivity, and fast handoff delay between APs (i.e., BSS transition.)

Establishing your selection criteria

Even with 802.11T, there will never be a one-size-fits-all list for selecting the "best" Wi-Fi client. One company may value receive sensitivity and distance over throughput at close range; another may give priority to Quality of Service controls for multimedia. Thus, every company must establish its own prioritized list of criteria for concretely evaluating and comparing Wi-Fi clients. Requirements that you may want to consider when creating your own short list include the following:

  • Physical Interfaces (PCI, PCMCIA, USB/version, SDIO)
  • OS(s) and Version (XP, 2000, MacOS X, Windows Mobile, Symbian)
  • Radio Standards (802.11a, b, and/or g, proprietary, domains)
  • Encryption needs (WEP, WPA (TKIP), WPA2 (AES-CCMP), WPA with AES)
  • Authentication needs (shared key, Personal (PSK), Enterprise (802.1X))
  • 802.1X EAP Types (EAP-TLS, EAP-TTLS, PEAPv0, PEAPv1, LEAP)
  • QoS Control (WMM, WMM Power Save)
  • Fast Roaming (802.11i Key Caching, Preauthentication, Proprietary)
  • Receiver Sensitivity
  • Transmit Output Power
  • Data Rate @ Range
  • Application Throughput
  • Battery Life
  • Bundled Client Software and Distribution / Installation Aids
  • Centrally-Configured Profile Support
  • Trouble-Shooting Tools and Diagnostic Aids
  • Site Survey / Discovery capabilities
  • 802.11h Dynamic Frequency Selection and Transmit Power Control
  • 802.11d Additional Regulatory Domain support
  • Environmental requirements (indoor/outdoor use)
  • Warranty and Vendor Support, existing relationships
  • Certifications (Wi-Fi, CCX, Microsoft)
  • Interoperability requirements (with AP/switch proprietary features)

To identify Wi-Fi client products that support some of these criteria, visit the Wi-Fi Alliance Certified Products page. For example, you can use the certification search page to find embedded clients that support 802.11g with WPA2-Enterprise and WMM. You'll need to research vendor websites and spec sheets to identify Receiver Sensitivity, Range, Interface, and OS requirements. A quick look at client configuration manuals can provide insight into administration and trouble-shooting utilities. Once you've narrowed your candidate list, there's no substitute for in situ benchmark tests, comparing factors like throughput and battery life in your very own real-world environment.

Establishing a Wi-Fi client selection process may not be easy, but making good client purchase decisions will pay dividends over the long run. You'll be in a better position to predict actual performance when upgrading APs or installing new ones. When users encounter problems, you'll know exactly what tools they have in front of them to assist with diagnosis and resolution. Better yet, you may reduce the number of help desk calls by avoiding those Wi-Fi clients that are cranky or downright incompatible with your carefully-selected APs and switches.

 

About the author: Lisa Phifer is vice president of Core Competence Inc., a consulting firm specializing in network security and management technology. Phifer has been involved in the design, implementation, and evaluation of data communications, internetworking, security, and network management products for nearly 20 years. She teaches about wireless LANs and virtual private networking at industry conferences and has written extensively about network infrastructure and security technologies for numerous publications. She is also a site expert to SearchMobileComputing.com and SearchNetworking.com.

This was first published in March 2006

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