WLan faces performance troubles

French researchers say they have pinpointed a problem in wireless Lan technology that could severely impair the performance of newer high-speed networks. Engineering experts at France's Centre Nationale de la Recherche Scientifique (CNRS) in Paris have demonstrated how a slow device connected to WLan (wireless Lan) hotspot can cause an entire network to drop to a slower speed, citing a common channel access method as the cause, said researcher Andrzej Duda. The researchers have focused on performance anomalies found in products based on the IEEE 802.11b standard. They observed that when one wireless device, such as a notebook, connects to a WLan at a lower bit rate than other devices - because it is too far from the access point, for example - performance of the other devices on the network becomes noticeably degraded. The explanation has to do with the CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) channel access method, according to Duda. This method, sometimes referred to as the "listen before talk", guarantees equally long-term channel access probability to all devices. In other words, when a device with a low bit rate captures the channel, it penalises other devices using a higher rate by degrading the speed of their connections. The CSMA/CA channel access method is standardised in the 802.11a, b and g standards, Duda said. Read More.....