followup question on rate selection

Krishna Ramachandran krishna at cs.ucsb.edu
Thu Mar 11 21:39:20 EST 2004


I played around with the rate selection algorithm in hostap. It seems 
like the driver uses s/w based rate selection only for the master mode. 
I would really appreciate it if someone could tell me or point me to 
some resource that explains how the hostap driver does rate selection. I 
could dive into the code and understand how it functions, but I am 
looking for the easy way out :)

thanks

-------- Original Message --------
Subject: rate selection in the driver
Date: Wed, 10 Mar 2004 18:41:09 -0800
From: Krishna Ramachandran <krishna at cs.ucsb.edu>
To: hostap at shmoo.com

Hi,
    I have an adhoc network consisting of a bunch of nodes with prism2
wireless cards (netgear ma401). the cards are set to choose the rate
automatically. I have several questions related to how hostap selects
the transmit rate:

1) In the code, the driver chooses the rate based on the auto rate
fallback (ARF) scheme. It seems like the rate at a transmitting station
is selected based on the variable "tx_since_last_failure", which is
incremented for each packet transmitted, no matter which neighboring
station the transmitter speaks to. If this is true, I think the
intuition behind designing it this way was because stations usually talk
only with the access point and hence it makes sense not to differentiate
based on the receiving station. However, this assumption doesn't hold
true for the 802.11 IBSS (adhoc) mode. Is my thinking right?

2) If my thinking is correct, is there a solution to select the rate
based on how the link to each neighbor performs?

3) Are rate selection schemes implemented in the firmware different? Is
there any documentation on the Internet I can use as a reference?

thanks in advance,
-- 
-Krishna

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-- 
-Krishna




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