Blog Host: Lisa Phifer READ ENTIRE BIO

A new guest expert will be fielding questions at the Expert Answer Center next week, but I'll still be answering your wireless questions every month at SearchMobileComputing.com. The wireless industry is evolving quickly, greatly expanding network reach and changing the way we do business. No matter how much I research and experience, it seems that there's always something new to learn. And that means there will always be new questions to ask and insights to share, so keep those brain-teasers coming!

Ciao for now,
Lisa Phifer
Posted by Lisa Phifer WLAN interference
29 JUL 2004 06:00 EDT (10:00, GMT)
I was on a conference call yesterday when someone on the call lost network connectivity because their 802.11b/g wireless router misbehaved. They said this problem happens often when they're on the phone. A cordless 2.4 GHz phone. Aha! There's an excellent chance this problem is being caused by radio interference.

Will putting the phone's base unit in another room solve the problem? Not very likely, because the handset and base use radio waves in the 2.4 GHz band to communicate. As long as the handset and router are near each other, interference will occur, especially during a call when more information is exchanged between the base and handset.

A better answer is to move either the wireless LAN or the cordless phone to another part of the radio spectrum. That means purchasing a new 802.11a router and adapter(s) OR purchasing a new 5 GHz cordless phone. Personally, I'd buy a new phone, but if you've made a big investment in 2.4 GHz phones and have just one router and adapter, then moving to 802.11a might be more attractive.

Not all cordless phones and wireless routers interfere with each other, but some product combinations definitely do. Similarly, not all microwave ovens generate noise on your wireless LAN, but "leaky" ovens definitely will. In general, if your wireless LAN misbehaves intermittently but regularly, keep a log of what's happening in your office whenever that problem occurs to see if you can spot a pattern. Spectrum analyzers can be needed to diagnose tough problems, but sources of interference can often be found through simple observations and trial-and-error resolution.
Posted by Lisa Phifer Hi-Ho MIMO
28 JUL 2004 13:30 EDT (17:30, GMT)
802.11 channels are shared by all stations associated with an access point, whether the AP is operating alone or as part of a wireless LAN "switch." This limits aggregate throughput of the entire WLAN to the capacity of that channel, minus overhead. Multiple Input Multiple Output (MIMO) changes this by using advanced antenna technology.

MIMO is now being considered by the IEEE as the starting point for IEEE 802.11n, the next-generation radio standard that promises data rates in the 100 Mbps range. Whether MIMO or its successor becomes 802.11n or not is still far in the future, and many other proposals are under consideration. In the meantime, some vendors are moving ahead with "pre-802.11n" MIMO to improve speed and range in heterogeneous WLANs.

MIMO takes advantage of multi-path, a radio phenomenon where signals from a given transmitter bounce off obstacles between the sender and receiver. APs implementing MIMO sample arriving signals to choose the best available path for future communication with each station. A good summary of MIMO can be found in this NetworkWorld article, written by Carl Temme.
Posted by Lisa Phifer Where Wireless LAN meets WAN
27 JUL 2004 14:00 EDT (18:00, GMT)
As a mobile wireless enthusiast, I have been waiting nearly a decade for one compact device that does a good job of supporting voice calls and data transfer over wide-area and local-area wireless. Hewlett-Packard's recently announced iPAQ h6315 sounds like it will be a positive step in that direction.

This new iPAQ PDA will include built-in Wi-Fi, Bluetooth and T-Mobile GPRS adapters. Ideally, it would switch seamlessly between wireless WAN and LAN services -- for example, continuing a file transfer started at a Wi-Fi hotspot without interruption over GRPS when you leave the coverage area. The h6315 can't do that yet, but it can detect hotspots automatically and launch new sessions over the fastest available network (GPRS or Wi-Fi). Depending upon the hotspot, login may be required before Wi-Fi use. Bluetooth is included primarily for wireless headset connection, and voice calls can only be placed over GPRS or (when GPRS isn't available) GSM networks.

Much more is needed before we'll see non-stop voice and data roaming over high-speed wireless WANs and LANs, but products like this one bring us closer to the day when we can carry a single device that keeps us connected 24/7, without making us think about wireless network types and coverage areas.
Posted by Lisa Phifer Finding Wi-Fi hotspots
26 JUL 2004 19:20 EDT (23:20, GMT)
Before I leave home on a trip, I gather all the info I might need while traveling: my flight numbers, my hotel address, the location of the nearest Starbucks and a list of nearby Wi-Fi hotspots.

Finding hotspots in advance saves me time and frustration later by predicting whether I'll have high-speed Internet access at the airports, hotels and cafes that I expect to visit. Reviewing provider lists and pricing helps me to figure out the most economical way to obtain Internet access when I'll have several options. When my best option is a café, carrying that establishment's phone number and hours with me can be handy.

This information can often be obtained from provider-supplied "Connection Managers" used to access commercial Wi-Fi hotspots. If you have an all-access account with one carrier, Connection Managers are a great way to locate hotspots where you'll find "free" (that is, previously paid-for) Internet access. Here are some common provider hotspot lists:

• Boingo Hotspot Finder
• iPass Access Point List
• T-Mobile Hotspot Finder
• Verizon NYC Hotspot Finder
• WayPort Hotspot Finder

• Hotspot Locations Public WLAN Directory
• Intel's Hotspot Finder (powered by JiWire)
• JiWire Hotspot Locator
• NodeDB Community Wireless Node Project
• Wi-Fi Alliance Wi-Fi Zone Finder
• Wi-Fi Hotspot List
• WiFinder Directory

• The Certified Wireless Network Administrator (CWNA) program teaches you about radio technologies, equipment, site surveys and deployment steps. I keep the excellent CWNA Study Guide on my desktop for handy reference.

• The Certified Wireless Security Professional (CWSP) program builds on what you've learned as a CWNA, expanding your knowledge of wireless security threats, policies and available countermeasures.

• A new Certified Wireless Analysis Professional (CWAP) program has just been announced, with a study guide now under development. CWAP builds on the foundation laid by the CWNA program, focusing on 802.11 performance analysis and trouble-shooting.

• I'm remembering the airport hotspot that consistently blue-screened my laptop everytime I connected to that AP.

• I'm fondly recalling my first visit to a Starbucks hotspot, where I had no trouble surfing the Internet without being prompted for a login or credit card.

• I'm thinking about all the hotspots that offered me public or private IP addresses, warning that public IPs would expose me to always-on Internet connection perils.

• I'm wondering whether that's better or worse than hotspots that forced me through NAT, establishing my VPN tunnel but refusing to deliver encrypted traffic.

• I'm still shaking my head over the shared printers and folders exposed by fellow latte drinkers at hotspot after hot spot.

As the article explains, standard spectrum management mechanisms for dynamic adjustment of radio transmission power and frequency were initiated due to concerns about 802.11a interference in the 5 GHz band. 802.11a interference hasn't been an issue here in the U.S., where 5 GHz is far less crowded than 2.4 GHz. But elsewhere (particularly in Europe), the 5 GHz band is already home to a few critical military radar systems. The idea behind 802.11h was to make 802.11a radios sensitive to those existing systems, automatically sensing interference and avoiding it, either by reducing output power, changing channels or both.

That may have been the motivation for 802.11h, but interoperable spectrum management mechanisms for Dynamic Frequency Selection (DFS) and Transmit Power Control (TPC) clearly have other benefits. APs that implement 802.11h can work to avoid interference with each other, minimize power (battery) consumption and self-tune to environmental changes that impact radio performance. To learn more about 802.11h, read Michael See's article or download the 802.11h-2003 standard from the IEEE Web site.
Posted by Lisa Phifer Finding 802.11 networks
20 JUL 2004 06:00 EDT (10:00, GMT)
If your company hasn't yet taken the 802.11 plunge, that doesn't mean that your office is Wi-Fi-free. Unless you're far from other businesses, 802.11 APs owned by neighboring companies may transmit signals that reach your location. Employees may have deployed 802.11 on their own, using inexpensive APs or peer-to-peer connections between laptops. Vendors, contractors, customers and other visitors may carry 802.11-enabled devices into your office without even realizing it. In fact, odds are actually pretty darn good that 802.11 has found its way into your office.

How can you tell? Try using a basic WLAN discovery tool, commonly referred to as a "Stumbler." Such tools are both freely available and easy to use. All you need is a laptop with an 802.11 network adapter and a discovery tool that supports your OS and adapter. Here's a short list of freely available "Stumblers" to help you get started:

• Dstumbler (BSD)
• MacStumbler (MacOS X)
• NetStumbler (Windows)
• MiniStumbler (Pocket PC)
• WaveStumbler (Linux)

If you discover 802.11 WLANs that don't belong to you operating nearby, there's little you can do except be aware they exist and warn employees not to connect to them. If you find unauthorized APs or adapters installed in your facility or on company laptops, you can take steps to eliminate them or make sure they're being used securely. Either way, forewarned is forearmed, so stop, look, listen and discover what's out there.
Posted by Lisa Phifer Hear ye! Hear ye! IEEE 802.11i gets ratified!
19 JUL 2004 06:30 EDT (10:30, GMT)
The big news in 802.11 Wi-Fi wireless this month is the long-awaited ratification of IEEE 802.11i, the new standard for Media Access Control Security Enhancements.

To date, Wi-Fi has been very successful in the residential market and key verticals but has lagged in the enterprise, due in large part to security concerns. Polls show that many companies are experimenting with Wi-Fi on a small scale but holding back on corporate-wide Wi-Fi rollouts. The improvements defined by 802.11i should help lift that barrier.

Although you'll find a number of products on the market that support 802.11i features like AES encryption, certified interoperable 802.11i products won't start hitting the shelves until September. That's when the Wi-Fi Alliance expects to announce the first set of 802.11i products that have passed WPA2 testing.

WPA2 is an extension of WPA, the Wi-Fi Protected Access upgrade that's been included with many new 802.11 products shipped since last summer. To learn more about WPA, WPA2, vendor plans and Wi-Fi Alliance interoperability testing, read this WLAN Advisor Tip that I wrote last week for SearchMobileComputing.com.

So how about it? If you have a WLAN in your home or office, do you plan to upgrade to WPA2? If so, when? If not, why not? I would like to hear your thoughts; please send me e-mail on this topic. I may share some of that feedback in future Weblog postings, but message sources will remain anonymous unless your e-mail indicates you wish to be named.
Posted by Lisa Phifer