Wireless LANs: Configurations and ConsiderationsTHE WIRELESS LAN ENVIRONMENTVocollect Talkman® terminals are specifically ...
coverage in this section. The following table summarizes Vocollect’srecommendations for specific configuration settings. N...
within transmission range. In general, a lower power output setting of 30mW or soin the AP better approximates the range o...
security system imposes in terms of expense and administration, the value of thedata being protected, and the likelihood o...
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WLAN considerations v2.2

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Consideraciones sobre la red inalámbrica a tener en cuenta al momento de implementar una solución de Vocollect

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WLAN considerations v2.2

  1. 1. Wireless LANs: Configurations and ConsiderationsTHE WIRELESS LAN ENVIRONMENTVocollect Talkman® terminals are specifically designed to provide reliable andforgiving voice operation under a wide variety of operating conditions. However,just as all wireless terminals, the Talkman terminal relies upon the underlyingwireless communications infrastructure to deliver data in a reliable and timelyfashion. A properly installed and operating wireless communications system iscritical to successful deployment and use of the Talkman® terminal. Based onVocollect’s experience in integrating products into hundreds of wirelessenvironments, this document discusses recommended equipment and best practicesfor problem-free implementation.Basic wireless LAN requirements: • IEEE 802.11b or IEEE 802.11g (802.11b compatible) wireless LAN • Must be WiFi certified for interoperabilityWiFi certification can be verified at the WiFi web site athttp://www.wirelessethernet.com/OpenSection/certified_products.asp?TID=2 orrequest a copy of the WiFi certificate from the wireless LAN manufacturer.ACCESS POINT HARDWAREDue to the popularity of the 802.11b/WiFi wireless, and the subsequent economiesof scale, the cost of wireless LAN Access Points (APs) have dropped dramatically inrecent years. But before shopping based on price alone, be aware that there are twoclasses of APs: SOHO and Commercial.SOHO APs are designed for small office/home office environments (hence thename) and are the least expensive. However, since home/small offices rarelyrequire more than one AP and have very few users, SOHO APs place little emphasison factors like roaming or user capacity. On the other hand, commercial APs aredesigned for high speed roaming, large numbers of users, and add other importantfeatures such as remote management, power management, dual antennas, Powerover Ethernet, network security, etc.Bottom line: don’t be tempted to go cheap since everything else in your system willuse the wireless network as a foundation.ACCESS POINT CONFIGURATIONThere are many options when configuring a commercial Access Point and there aremany manufacturer specific parameters, so no attempt is made for comprehensiveVocollect, Inc. Proprietary Information Page 1 of 4
  2. 2. coverage in this section. The following table summarizes Vocollect’srecommendations for specific configuration settings. Note that none of thesesettings are absolutely required, but from experience, they are stronglyrecommended. A more detailed discussion of each setting follows the table. Data Rate Restriction of data rates to use 2Mbps and 5.5Mbps only Antenna Diversity Dual antenna diversity enabled Output Power 30mW-50mW Traffic Filtering Filter out extraneous broadcast traffic Security WEP at minimum, WPA or better recommendedDATA RATEWiFi APs are designed to operate at varying data rates. An 802.11b AP uses datarates of 11, 5.5, 2, and 1 Megabit(s) per second (Mbps). When a mobile terminaldevice is communicating with an AP with a strong signal, the fastest data rate(11Mbps) is used. As the mobile terminal moves away from the AP and the radiosignal diminishes, a lower data rate is used to minimize data errors. This loweringof data rates continues until a reliable signal cannot be maintained at the minimumdata rate.APs can be configured to either operate at all of the available data rates or berestricted to only specific data rates. Due to the roaming nature of mobile terminals,the inefficiencies in the AP when shifting data rates and the low data volumeto/from mobile terminals in general, overall performance can often be enhanced byrestricting data rates to those which are statistically dominant. This results in bettereffective response times for the user. Consequently, Vocollect recommendsconfiguring the AP such that only 5.5Mbps and 2Mbps are used.ANTENNA DIVERSITYCommercial Access Points generally support two antennas. The purpose of the twoantennas is to address a RF problem called multi-path interference where radiosignals at high frequencies (such as those used by 802.11b) can bounce off RFreflective surfaces and cancel themselves out. Using two antennas allow for twoseparate receive paths so that a signal null is unlikely at both antennassimultaneously. This is especially important in mobile environments or where metalstructures exist in the AP coverage area.Of course in order for antenna diversity to work, the AP software configuration mustbe set to use two antennas. AP manufacturers often refer to this feature as antennadiversity.OUTPUT POWER & MUTUAL INTERFERENCEMost commercial APs allow the configuration of output power. The temptationexists to simply set the output power at maximum for a large RF coverage area.However, in order for two-way communications to function properly, the coveragearea of the AP should approximate the coverage area of the mobile terminal. Thisensures that each can “hear” each other without drowning out other RF devicesVocollect, Inc. Proprietary Information Page 2 of 4
  3. 3. within transmission range. In general, a lower power output setting of 30mW or soin the AP better approximates the range of a mobile device and limits mutualinterference.Mutual interference can also be minimized by careful placement of the AP wheninstalled. In general, APs should be installed such that the RF coverage area of oneAP has a low percentage overlap into the adjacent coverage area of a neighboringAP. Lower power settings can make overlap more manageable. Your WLANinstaller can best advise you of the optimum power setting through a site survey.BROADCAST TRAFFICWhen deploying Wireless LANs, it is especially important to eliminate extraneousbroadcast traffic from being passed from the wired LAN. Broadcasts are widelyused by Microsoft, Novell, and other enterprise network operating systems. Bydesign, broadcast packets require all receiving devices to process the data theycontain; even if the data is not applicable to the receiving device. This unnecessarypacket processing on battery powered mobile devices results in poor user responseand poor battery performance.Broadcast traffic can be filtered by using settings in the AP, or through the design ofthe wired LAN (e.g. VLANs). Consult with your WLAN vendor to determine thebest method for your architecture.SECURITYNo recommendation would be complete without some discussion on wireless LANsecurity. A comprehensive discussion is beyond the scope of this document, but it isimportant to mention that at least some security is strongly recommended. At thevery minimum, WEP (Wired Equivalent Privacy) security should be enabled. Eventhough WEP encryption can be cracked, it is only vulnerable when enough data ispassed while on a single AP (roughly 500,000 uniquely keyed packets). Most mobileterminal applications do not pass enough data while not roaming and under thecoverage of a single AP to allow cracking. The very mobile nature of the terminal isa substantial barrier against WEP cracking.Of course, better security is always more desirable. The next step up from WEP isthe WPA/PSK (Wireless Protected Access/Pre-Shared Key) protocol developed bythe WiFi organization. Deployment of WPA/PSK is strongly recommended, as itovercomes the vulnerability of WEP but does not require a security server and theassociated overhead costs.Other more advanced security methods are available and may be more desirable foryour organization. The more advanced the security, the more overhead that isrequired for additional equipment and administration, so do not automaticallyassume that the most sophisticated security is best for you. The right amount ofsecurity for your organization will be a balance between the burden that your dataVocollect, Inc. Proprietary Information Page 3 of 4
  4. 4. security system imposes in terms of expense and administration, the value of thedata being protected, and the likelihood of an incursion.SITE SURVEYRF Site Surveys are the recommended method to optimize & verify WLAN coverageand ensure that the WLAN environment is clear of any unintentional or outsideinterference.In recent years the cost of WLAN APs has fallen dramatically. This has precipitateda tendency within IT departments to skip the site survey process entirely and simplyinstall APs at regular intervals within a building. This method is not recommended.APs spaced too closely can cause them to interfere with each other. APs spaced toofar apart will result in coverage gaps.Engagement of a reputable network integrator with WLAN expertise is highlyrecommended. The integrator should be able to provide a spectrum analysis of yoursite to identify any potential sources of interference, be able to design your wirelessnetwork, recommend antenna options, guarantee needed RF coverage, perform aphysical site survey, and provide comprehensive documentation once the WLANinstallation is complete.Site survey related recommendations:• Assuming a spherical coverage area, the coverage of one AP should ideally overlap an adjacent AP’s coverage area by 25% or less unless non-interfering channels usage can be guaranteed. Since antennas radiate in three dimensions, radiation patterns that extend above and below onto adjacent floors must be considered.• Since each type of mobile terminal have different radio and antenna performance characteristics, surveys should be performed using the mobile terminal type being deployed. If this is not possible, the site surveyor should approximate mobile terminal performance as closely as possible by using a similar terminal, or by adjusting power as appropriate.• Ideally, site surveys should be performed with the installation environment as close to its final configuration as possible. For example, when installing in an environment where inventory is stored, the inventory should be in place in the storage locations prior to performing the RF survey. This ensures that radio signals will not be blocked by the final state of the environment.ADDITIONAL INFORMATIONThere are a number of excellent resources for additional information. Here are somelinks to articles and books: • http://www.oreillynet.com/pub/a/wireless/2005/05/02/80211myths.html • http://www.wi-fiplanet.com/tutorials/article.php/1116311 • 802.11 Wireless Networks: The Definitive Guide, Second Edition by Matthew Gast, ISBN 0-596-10052-3Vocollect, Inc. Proprietary Information Page 4 of 4

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