RE: throughput question

The effective throughput for the 11g user will drop, because the 11g
standard requires the use of a "protection mechanism" whenever an 11b
client is associated at the AP or at an overlapping AP that is on the
same channel.  The reason that a protection mechanism is required is
that an 11b station cannot decode frames sent at 11g data rates.  At
best 11g frames seem like noise to an 11b station.
 
The protection mechanism does require that an 802.11 control frame
(usually a CTS frame that is addressed to the sender of the data frame,
i.e., a "CTS to self") is sent before the data frame.  This control
frame must be sent using an 11b data rate, so that 11b stations will be
able to receive it and stay off the air while the 11g data frame is
transmitted.
 
So because this extra frame needs to be transmitted with every data
frame, the overall throughput will drop, even when the data frames are
sent at the 11g data rates.  There is no requirement that the data
frames use 11b data rates when 11b stations are present, as is often
claimed.

 -Bob
  

-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of
Mary
Sent: Tuesday, January 04, 2005 10:22 PM
To: [email protected]
Subject: [BAWUG] throughput question


If I have a .11g access point and a user using a .11g card and another
user associates with a .11b card does the transfer rate drop for the
user using the .11g card?  
 
Thanks so much...

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