The largely unsolved hurdle of contention for access-point capacity keeps voice-over-wireless systems vulnerable to poor-quality calls, as well as calls marred by dropouts if too many voice or data users are trying to connect to the network simultaneously.

The IEEE is targeting the issue in a forthcoming standard called 802.11e, which will add quality of service (QoS) capabilities to wireless networks. The idea is simple: Set priority levels for both traffic and users so the capacity can be distributed better. With 802.11e, an access point could give voice calls priority, lessening the chances of dropouts. Data users might see their connections become more intermittent, but the "bursty" nature of most data traffic will mask that fact much longer than is possible for streamed traffic, such as voice.

The 802.11e standard will also permit scheduling, so traffic can be better managed. Scheduling helps the access point control its own usage of the wireless network to better match the priorities of the client traffic.

The 802.11e standard is expected to be ratified this spring and should start appearing in products this summer. Already, many vendors have deployed pieces of it based on the draft standard.

The Wi-Fi Alliance, an industry consortium, has ratified some pieces to give vendors a head start and to dissuade them from promoting proprietary solutions.

Deployed by some vendors, these pre-802.11e standards are Wireless Media Extension (WME) for prioritisation Wi-Fi Scheduling Media (WSM) certification for scheduling.

Even before 802.11e became a standards effort at the IEEE, vendors tried to address the problem of contention. Several of them - including Avaya, Cisco Systems, Mitel Networks and Nortel Networks - have licensed SpectraLink Voice Priority protocol, which gives basic prioritisation to voice traffic on an IP network.

SpectraLink plans to replace SVP with 802.11e when the standard is ratified.