hostapd 802.11n Throughput Optimizations
Galen P Zink
galen at zinkconsulting.com
Sun May 31 05:36:38 EDT 2009
I'm trying to optimize 802.11n throughput with hostapd. Before I begin
tweaking with the ath9k drivers, I'd like to make sure hostapd is
setup for optimal performance.
Software: Debian unsable with 2.6.29-2 kernel; latest compat-wireless
bleeding edge snapshot; <1 day old hostapd snapshot. Dedicated system
for wireless testing.
Hardware: 2 GHz Core Duo CPU, 2 GB RAM, AR5008 miniPCI-e card (3
Objective: Maximize 802.11n throughput at 5 GHz, assuming complete
control of all stations on the access point. 40 MHz channels desired.
Right now, hostapd appears to be yielding lower-than-expected
performance, approximately half that of an AR5008 access point. Given
the AR5008 card I have is more powerful and has (arguably) better
antennas, and a vastly faster CPU, it seems such a large gap may
likely be a software issue.
I have appended my hostapd.conf file below. I started with the
template and adjusted items as I saw appropriate. I did not try to
change too much. I welcome comments and suggestions!
I would greatly appreciate comments on the best ways to debug /
monitor hostapd. -dd is not enough resolution. It would be preferable
if I could do something less granular than reviewing every wireless
frame, of course; something like broad statistics on frame size, re-
transmits, bitrates, signal to noise levels, etc. would be very nice.
I also am hoping for some clarity on the ht_capab flags as well. I
expected [GF] to ban all legacy clients, but it doesn't. What does it
do? Is there a way to enforce 802.11n only? Does HT40+ versus HT40-
have any impact on client / radio compatibility? Are there any
disadvantages to enabling [LDPC] - I'd expect only benefits, unless
the CPU were overloaded? I believe ath9k still does not support STBC;
is there any harm to having it on, or is STBC somehow handled by
My apologies in advance if I missed documentation on the above items
# Low priority / AC_BK = background
# Normal priority / AC_BE = best effort
# High priority / AC_VI = video
# Highest priority / AC_VO = voice
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