rate selection in the driver

Krishna Ramachandran krishna at cs.ucsb.edu
Wed Mar 10 21:41:09 EST 2004


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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