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802.11r : Handling tricky issues for Wireless VoIP

A look at some of the challenges of Wireless VoIP.

In March, 2004, a new unit was formed within the 802.11 wireless neworking IEEE group, according to the group's news bulletin. The group's task is to address an issue similar to one that proved to be a major technical hurdle in the early days of cellular telephony—namely, the handoff problem for wireless 802.11 VoIP handsets when they need to switch service from one access point to another.

The underlying physical problem is latency, and the ITU recommends that for voice traffic such latency not exceed 150 ms (more than that can cause problems with a user's ability to hear and conduct a call). Because of other factors involved that can't be overcome, such as the actual transmission time and needs for users to authenticate with the access points they might use, this puts some pretty tight time constraints on how hand-offs should occur, and how quickly they must occur, to keep calls going uninterrupted.

The working group is currently known as the Fast Roaming Study Group and will keep working under that name until they officially become a task group. In the meantime, they're investigating a technology known as Fast-BSS-Transition (BSS stands for "Basic Synchronized Subset" an ITU term used to describe a group of wireless radio or other communications receivers that can handle signals for users moving among and between their coverage areas).

As far as I can tell, not much has been reported about this effort since original reports were circulated in late March, except for a Call for Interest on Fast Roaming in the 802.11i Working Group on July 20th. Since this deals with MAC-layer security, it stands to reason that it should address security needs for wireless handsets among other wireless devices, and makes sense as a topic that should bring both groups together.

It will be interesting to see what kind of results come out of this effort. Though roaming is possible today within limited areas (and works best with equipment that "pre-authenticates" handsets on adjacent access points to make connection hand-offs happen faster) it's nowhere near the capability of current cell phone technology. Whether or not sufficient standards can emerge to enable such reach is an interesting problem to understand and solve, as will be the coordination and handling necessary to deal with usage fees or charges. As all this unfolds, lots of people will be watching with great interest!

Ed Tittel is a regular contributor to numerous TechTarget Web sites, and the author of over 100 books on a wide range of computing subjects from markup languages to information security. He's also a contributing editor for Certification Magazine, and edits Que Publising's Exam Cram 2 series of cert prep books. E-mail Ed at

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