A Wi-Fi client connects to a network through an infrastructure endpoint device such as an access point (AP). When the client moves to a position where its connection to that AP becomes suboptimal, the client will try to switch to an AP that provides better connectivity. The process of switching from one AP to another is called roaming.

The challenge is to maintain an active network connection while you roam. Many business-critical applications require a persistent network connection, and a disruption of as little as 100 milliseconds can cause an application to fail, resulting in lost data and lost productivity.

To roam effectively, a client must recognize when its current connection is suboptimal, scan the airwaves for a better AP, select the best AP, roam to it, and reauthenticate to the network. Many client devices do a poor job of selecting an AP and take a long time to reauthenticate to the network, especially when using Extensible Authentication Protocol (EAP) methods with IEEE 802.11i, the ratified standard for Wi-Fi security. Organizations should strive to use clients with proven capabilities for fast and secure roaming in any environment.

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For most of today's retailers, solid Wi-Fi client device security is essential for compliance with the latest version of the Payment Card Industry Data Security Standard (PCI DSS), version 1.2. Such security can be achieved by following three best practices identified in the paper:

• Ensure that a Wi-Fi client device can gain access to your wireless LANs (WLANs) only using WPA2-Enterprise with a strong EAP type.
• Configure every trusted Wi-Fi client device to connect only to trusted APs.
• Use ongoing monitoring to demonstrate the effectiveness of your WLAN security approach.

PCI DSS v1.2 classifies both WPA and WPA2 as sufficient replacements for WEP, which must be phased out of existing WLANs by mid-2010. Researchers have reported that a vulnerability in the WPA encryption method of TKIP may enable attackers to decrypt TKIP-encrypted data, but those researchers have provided no evidence that a practical tool for cracking an actual TKIP key or deciphering TKIP-encrypted data packets is imminent. Still, because the TKIP vulnerability does not exist with the WPA2 encryption method of AES-CCMP, retailers should plan now to phase out client devices that do not support WPA2.

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IEEE and industry standards define how a Wi-Fi radio interoperates with a wireless LAN infrastructure, and the Wi-Fi CERTIFIED™ seal ensures interoperability. For many organizations that rely on mobile devices, however, Wi-Fi CERTIFIED is not enough. These organizations need assurance that their mobile devices will interoperate with a Cisco wireless LAN (WLAN) infrastructure and support Cisco WLAN innovations for enhanced security, mobility, quality of service, and network management. The Cisco Compatible seal, earned through the Cisco Compatible Extensions (CCX) program, gives organizations the assurance that they seek. Because the CCX specification is a superset of that used for Wi-Fi certification, CCX encompasses standards in addition to Cisco innovations.

CCX has been an overwhelming success in the laptop world, where a few silicon providers do all of the work in their reference designs for radios. Reference designs are insufficient for business-critical mobile devices, however, and the task of modifying reference-design software to support all required CCX features is too much for most mobile device vendors. An attractive option is to use Wi-Fi solutions from Summit Data Communications, because Summit solutions already are certified for CCX.

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• CCX for Mobile Computers (Adobe Acrobat Document)
• CCX for Medical Devices (Adobe Acrobat Document)

Boasting throughput 10 times greater than that available with previous wireless LAN (WLAN) standards, the IEEE 802.11n standard is the buzz of the Wi-Fi industry, and Wi-Fi infrastructure vendors are promoting little but their latest 802.11n products. The great performance of 802.11n is the result of enhancements that also yield improved quality of service, greater range, and improved predictability of coverage.

When you deploy 802.11n infrastructure, all 802.11n benefits except greater throughput accrue to client devices that use pre-802.11n radios. Because business-critical mobile devices such as mobile computers and medical devices run primarily data applications and not multimedia applications, those devices tend to have relatively modest throughput requirements. The primary benefit of deploying 802.11n on those devices will be to enable other devices, such as laptops, to gain the full throughput benefits of 802.11n.

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Industrial networks present greater challenges to networking professionals than do residential and commercial networks. The 5 GHz operating band has traditionally presented greater challenges than the 2.4 GHz band particularly as they relate to range and performance.

Despite this, when properly designed as part of a dual band network, operation on the 5 GHz band can add substantially greater network capacity without sacrificing performance and reliability. The need to incorporate 5 GHz operation into industrial Wi-Fi networks will increase over time as the 2.4 GHz band becomes more overused by a variety of devices.

Summit recommends the incorporation of the 5 GHz operating band:

• Because the 802.11a and 802.11n standards that operate in the 5 GHz band provide for data rates no lower than 6 Mbps, APs should be placed such that client devices maintain connectivity at data rates of 6 Mbps or greater. Given the mission critical nature of industrial Wi-Fi networks and given the ever-increasing and unpredictable application requirements for these networks, it is important that networking professional design their Wi-Fi networks for operation at data rates substantially above their current application requirements.
• When placing APs for operation at a given data rate, this spacing should be determined when operating on the 5 GHz band rather than the 2.4 GHz band. This is particularly the case when operating according to the 802.11a standard.
• The spatial multiplexing capabilities of the 802.11n standard provides for substantial performance and reliability improvements over legacy standards (802.11a in particular). 802.11n infrastructure devices are widely available today and provide these benefits to 802.11n and legacy 802.11a, 802.11b, and 802.11g client devices. To allow for reliable operation on the 5 GHz band in particular, network administrators should upgrade to an 802.11n infrastructure as resources allow.
• Although 802.11n radios are not widely available on the small handheld mobile devices that are often found in industrial Wi-Fi networks, dual band 802.11a/b/g radios are becoming increasingly available.. These dual band client devices gain much of the performance and reliability benefits provided by an 802.11n infrastructure. By deploying these dual band client devices in conjunction with an 802.11n infrastructure, network professionals gain the capacity of the 5 GHz band and much of the benefit of 802.11n without waiting for the availability of 802.11n on all types of clients.
• Although the number of channels available in the 5 GHz band provides for increased network capacity, it also results in longer scan times which can impact performance and reliability. This is particularly the case when only passive scanning is allowed, as with DFS channels. Therefore, network architects should not configure APs for operation on DFS channels (unless absolutely necessary) and should remove these channels from the scan list on client devices.

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