A standards effort was launched today which should allow office Wi-Fi networks to handle voice calls. A group of vendors, including Airespace and Spectralink, has requested permission to create a Fast Roaming study group, working on handover between access points, within the IEEE standards body.
The IEEE already has a quality of service standard, 802.11e in progress, that can prioritise voice packets over data, but the new proposal is needed for the separate issue of handling phone calls when users move between access points within a wireless network. The original 802.11 Wi-Fi standard specified that users should be able to move to a different access point, but this "roaming" creates a brief interruption in the data stream.
The break has been made worse by security features implemented on Wi-Fi networks, ironically. When a user moves from one access point to another while making a voice call, an encrypted tunnel must be broken down through one access point and re-formed through the new one; if this process takes more than 50ms, the user will hear a break in the voice conversation. Vendors have reported hand-over times of more than 70ms.
"With the new security of 802.11i, there is a feeling that roaming has been slowed down and needs to receive a kick in the pants," said Bob O'Hara, director of systems engineering at Airespace, a wireless switch vendor which majors on voice over Wi-Fi, and a member of the study group.
The study group will start work on its proposed standard directly; the IEEE's bureaucracy cannot officially launch the standards project until the 802 executive committee has approved the "project authorisation request" issued by the study group, and passed it to its standards committee for final, final approval in March.
"Airespace is involved, because we agree that without a standard in this area there will be a pile of proprietary ways to do this," said O'Hara. "This affects VoIP handsets most severely today, but all 802.11 devices are affected to one degree or another." It also affects applications differently, he said, depending how tolerant they are to interruptions to the data flow.
Cisco has planned its own proprietary answer, in the form of extensions to its wireless products, and others have implemented different handover mechanisms. O'Hara hopes that the proposed standard irons out these differences. Other companies who have expressed interest in IEEE discussion groups include Symbol and Intel.
In the meantime, many people feel that current Wi-Fi standards cannot support voice reliably, with the addition of 802.11a being a popular suggestion to get round the problem (see our feature on voice on Wi-Fi).
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