Subject: [NEXTEL-1] One Slow User in Hot Spot Can Degrade Wi-Fi

From: Marcel <[email-masked]>
Date: Sun, 03 Aug 2003 13:44:38 -0400

-------- Original Message --------
From: Alison Lewis <[email-masked]>
Subject:  One Slow User in Hot Spot Can Degrade Wi-Fi

One Slow User In The Hot Spot Can Degrade Wi-Fi
Performance
July 31, 2003 (1:45 p.m. EST)
TechWeb News 

A group of French researchers said Wednesday that
they've spotted a flaw in wireless LAN technology
which could allow one slow user to drag down
performance of everyone connecting to a hot spot. 
Four scientists, who work for France's Centre
Nationale de la Recherche Scientifique (CNRS) in
Paris, said in their research paper that anomalies in
the IEEE 802.1x standard -- including 802.11a,
802.11g, and the most widely-used Wi-Fi protocol,
802.11b -- can result in degraded performance for all
accessing the Internet through a hot spot when just
one slow user connects. 

They cited an example where several users, who are
enjoying a fast 11Mbps connection because they're
close to the hot spot, see their performance
dramatically drop when a single user -- perhaps
because he is further from the access point --
connects at a sluggish 1Mbps. In that case, the French
experts said, all are punished for the sins of the
one: those users once connected at 11Mbps will see
their speeds dragged down to 1Mbps. 

The anomaly, they said, is inherent in the CSMA/CA
(Carrier Sense Multiple Access/Avoidance Collision)
access protocol, which guarantees equal access to the
hot spot by all devices. 

While the problem may not be readily apparent to users
-- especially when everyone accessing the hot spot is
engaged in relatively light-load activities, such as
browsing Web pages -- if just one user is downloading
files, or accessing audio or video via wireless,
others can be penalized

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