As seen with wired networks, most companies strive to implement wireless LANs from a single vendor in order to ease management of vendor contracts and network support. In most cases you can design a wireless LAN backbone consisting of access points from one vendor, but eventually you're likely to end up with client devices equipped with radio cards from different vendors.

This situation is most likely to occur if you're planning to support a variety of wireless applications. For example, you may decide to use Cisco access points and laptops having Cisco radio cards. There's no problem so far, but the addition of a device such as a Symbol barcode scanner (pre-equipped with a Symbol radio) will introduce another vendor's radio on the network. Since all the components comply with IEEE 802.11, then everything should be okay, right? Let's take a closer look before answering that question.

Consider performing roaming tests to determine whether a radio-equipped client from one vendor can successfully roam across access points of a different vendor.

Vendors have been successful making their products interoperate with others via 802.11 protocols; however, 802.11 doesn't specifically define how a radio in a client is supposed to roam from one access point to another. This enables one vendor to implement roaming different than other vendors. Don't be too alarmed, though, vendors have done a good job of providing cross-vendor roaming (but certainly don't count on it!).

To be safe, consider performing roaming tests to determine whether a radio-equipped client from one vendor can successfully roam across access points of a different vendor without causing errors or significant delays while transferring a file. Attach a PC to the Ethernet hub to act as a host, and set up the wireless client (e.g., a laptop) to send a file to the host via communications software such as FTP. An executable program, such as Adobe Acrobat, is a good file to send because you can try running the program on the host to verify whether the transmission was successful.

While the radio card is associated with one of the access points, initiate transmission of the file. After the transmission is approximately fifty percent completed, unplug the associated access point (forcing roaming to occur). The radio card should associate with the other access point and finish transmission of the file to the host. If the executable runs okay from the host, then roaming is successful.

Something else to consider is that it's common for vendors to include proprietary performance and supportability enhancements to their products in order to compete with their foes. These enhancements seldom work in multivendor wireless LANs, reducing functionality to only that provided by the 802.11 standard. Because of these issues, you'd better qualify the mixture of wireless LAN products that you plan to use before moving forward with the implementation.

Stay tuned. Next time we'll survey options for wireless connectivity via satellites.

» posted by ITworld staff

ITworld.com

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