Roaming

Although most SOHO (Small Office/Home Office) Wi-Fi network users incorporate only one wireless access point (AP) in their networks, it's possible to create a network with multiple access points, each access point serving a zone within an area too large for a single AP to serve. Such a network, incorporating multiple access points, is called an extended service set (ESS.) In an ESS, users with laptops and PDAs are able to roam about the entire area covered by the ESS and not lose their connections to the network. The several access points seamlessly 'hand off ' users who 'roam' from place to place, just as the cells in our cellular telephone network do.

At least that's how it should work in theory.

The problem is that this is one of the several 'soft spots' in the 802.11b Wi-Fi wireless networking specification. 802.11 dictates that roaming is permitted, and explains what should happen when clients roam from the influence of one AP into the influence of another. Unfortunately, the specification doesn't say how this roaming should be accomplished. Roaming isn't trivial, and requires some pretty detailed communication among the various access points within the ESS. The numerous manufacturers of access points have all implemented the details of roaming in different ways, most of which are incompatible with all the others.

What this means is that for an ESS to implement roaming correctly, all the access points in the ESS must be from the same manufacturer -and, ideally, of the same model. In general, access points designed for corporate rather than residential service work best in roaming installations. Some of the lower-end residential access points and wireless residential gateways don't implement roaming at all.

There is an 802.11 task group working on the roaming problem, and at this writing they are still hard at it. Their goal is to write a standard for roaming, which (when implemented by the major manufacturers) will allow access points from different manufacturers to partake in an ESS that allows roaming across all access points. This group is called the 802.11f task group, and it is standardizing a protocol called the Inter-Access Point Protocol (IAPP). Various flavors of IAPP exist among various manufacturers, but the 802.11f protocol will replace all the proprietary flavors with a single, universal protocol. Until 802.11f happens, roaming will remain a singlevendor solution, and you should inquire closely of the vendor of an AP model under consideration to make sure that it supports roaming among others of its own kind.



Jeff Duntemann's Drive-By Wi-Fi Guide
Jeff Duntemanns Drive-By Wi-Fi Guide
ISBN: 1932111743
EAN: 2147483647
Year: 2005
Pages: 181

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