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Wireless 802.11 spec pushes enterprise networks forward News Editor Amanda Mitchell sits down with wireless guru Matthew Gast to chat about the impact of the 802.11 spec on enterprise networks.

What are the most interesting activities occurring in the standards arena these days?
There is a lot going on in the IEEE right now. I think the 802.11n standard, which has the potential to offer a performance boost; the 802.11r work, which is important to voice over IP over wireless and other delay sensitive services; and 802.11u are the most interesting. What is happening with 802.11n?
Most importantly, the wait is finally over. After a great deal of contention in the task group, there is finally a draft. The standard is by no means done, but this is a significant step towards the eventual specification. We're very excited by this because 802.11n can provide a performance boost to wireless networks and we know that users always seem to figure out how to use whatever network capacity can be delivered. In the consumer market, higher-speed technologies are already a success, and there is a long history of enterprise technology following the consumer market.The standard itself is a substantial piece of work. It weighs in at almost 350 pages and changes some aspects of the way that the 802.11 [spec] operates. To increase efficiency, clusters of frames will "carpool" in units called aggregate frames. The simple transmit-acknowledge-transmit-acknowledge sequence that 802.11 [spec] has been known for most of its existence is being relaxed further, to allow whole packet bursts to be acknowledged efficiently. There are numerous options on the radio side, too, that allow frames to be transmitted from the best antenna and make best use of the radio link by making detailed measurements of it. You also said that progress has been made in 802.11r. What's happening?
The past two years have seen VoIP go from an interesting novelty to the mainstream. Wireless networks have much more restricted capacity and thus needed a push in the standards. When an 802.11 device moves between APs, it only has about 50 milliseconds to make the change. That's 50 ms to find a new AP, establish security, and set up quality-of-service parameters. 802.11r defines the procedures by which a client can request that QoS be set up before committing to the move, which makes the transition smoother. Pre-establishing QoS works very well in a wireless switch architecture because we reserve resources at the switch, so it's easy to keep the resources established in one place (the switch) while the other endpoint of that conversation moves around. In the longer term, this will also be useful for capacity management. In very dense networks, there may be reasons to move a station from a busy AP to a less loaded one, and 802.11r provides mechanisms by which the network could move stations rapidly. What about 802.11u?
The past few years have seen 802.11 become the default "on ramp" for Internet access. Previously, installing Internet access into a hotel meant bringing Ethernet to every room. Increasingly, connectivity is provided with 802.11, just as it is in airports, coffee shops, and even for guests at corporate offices. One of the problems with this profusion of networks is that in crowded areas, you usually can't be sure what services a network offers until after you've connected. 802.11u defines techniques for inter-working between different kinds of wireless networks, thus enabling 802.11a/b/g/n to become the on ramp to cellular networks or other future wireless networks like WIMAX. This group has started work on a standard that will help client devices use external credentials, say, from a cellular network to establish the right to use a network (authentication), present restricted services (for emergency calls), or simply indicate that it's possible to sign up to the network for a fee.

Matthew Gast is director, consulting engineering for Trapeze Networks and recently authored 802.11 Wireless Networks: The Definitive Guide, 2nd Edition (O'Reilly, April 2005).

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