Apparent TX speed boundary

James B. Hiller jhiller at
Sun Dec 12 00:49:56 EST 2004

Hi list!

I've got the following setup:

a.  DWL-520, Rev A2 running hostap 0.2.5 (PCI) on a dual Pentium Pro 200
linux 2.6.0 box that acts as my gateway machine - WAP/firewall/router/etc.
I have a Zcomax XI-325 antenna on the card; has a 6 ft lead, and gets the
antenna up about 6 feet off the floor.

b.  DWL-520, Rev A2 running on a dual AMD MP 2200 linux 2.6.9 box and the
applicable kernel driver for the Prism chipset.  Card uses stock whip
antenna on back of case.  Antenna is at desk height above floor, about
2.5 ft below and 3 feet over from AP antenna; LOS partially occluded by 
this box' case.

c.  DWL-520+ running on an AMD K6-III+/500 machine (desktop) running WinXP
SP 2 with latest driver for the card (Sep 03), and D-Link AirPlus configuration
and monitoring utility, ver 3.07 (latest).  Card uses stock whip antenna
on back of case.  Antenna is at desk height above floor, about 2.5 ft below
and 20 ft over from AP antenna; LOS occluded (almost bisected, almost
perpendicularly) by two sheetrock walls forming closet wall and room
separator wall.

Just moved machine (c) to XP from 98, so wanted to make sure all was still
good with the network (note:  never really spent any time checking transfer
speeds on this machine before, even though I've had all the hardware running
over a year).

So I fired up the XP ftp client on box (c) and hauled over a 75 MB file
from box (b) through (a).  Using the D-Link utility, which gives a nifty
little bar graph of TX and RX speed, I consistently get 2.5 Mb RX going
in this direction.  Moreover, if I move the file directly from (a) to (c),
I get about 4.5 Mb RX at (c).  But when I transmit to either (a) or (b)
from (c), using hostap 0.2.5, I'm getting peaks of right around 1 Mb, and
2-3 of 4 bars are staying around 550 Kb.

Also note that, until today, I HAD been using hostap 0.1.2 (!) - because
it was doing great!  And when I first started running this example
earlier in the day, BEFORE I moved to 0.2.5, I was still getting the
1 Mb TX "ceiling", but I was getting much higher averages - the other bars
were usually around 800 Mb.  So then I moved to 0.2.5, hoping it would
do something differently... and it did; slower.

The whole time this is going on, the D-Link configuration/link monitor
tool is showing the DWL-520+ TX speed (non-settable) as being 1 Mb, even
though in the configuration part of the tool I have hard set the card
TX speed to be 11 MB.

So what I'm wondering is, is there any possibility this apparent ceiling
is being set by the AP card, and is such in some way under the control of
hostAP such that I could adjust it?

I can provide info on interference sources, though methinks that doesn't
matter much.

DWL-520 particulars (both in (a) and (b) are identical):

NICID: id=0x8013 v1.0.0 (PRISM II (2.5) Mini-PCI (SST parallel flash))
PRIID: id=0x0015 v1.1.1
STAID: id=0x001f v1.7.4 (station firmware)

And the interface settings:

wlan0     IEEE 802.11b  ESSID:"default"  
          Mode:Master  Frequency:2.437GHz  Access Point: 00:05:5D:FA:5F:75  
          Bit Rate=11Mb/s   Sensitivity=1/3  
          Retry min limit:8   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality:0  Signal level:0  Noise level:0
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:1204  Invalid misc:3113   Missed beacon:0

(At this point, I've done the 75 MB transfer once in each direction).

At minimum, I'd like to get an idea of whether it's some inherent limitation
with the DWL-520+, or at least a process for determining what and where
the issue is.  Any advice, suggestions, ... thx!  (other than "call D-Link
tech support" - not an option :-))


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