Re: RTL 8187b - naughty behaviour

[seno <senada@t-online.de>]

Larry Finger <Larry.Finger@...> writes:

> I do not understand the poor performance. I have a device with the
> rtl8187b chip - USB IDs 0bda:8187. That is an ID for an rtl8187, but it
> does have the B chip. I use tcpperf to measure the transmit speed. At 2
> m from the AP with an indicated signal of -17 dBm, my throughput is 13
> Mb/s. At 10 m with a signal of -49 dBm, the transmit speed is 3.5 Mb/s.
> On the download using speedtest.net, I got 11.3 Mb/s at 2 m, and 2.64 at
> 10 m. I got 0.49 Mb/s upload at both distances as that is the speed of
> my line.
> 
> What happens if you use iwconfig to force a particular rate? At what
> setting is your throughput maximized. I don't think there is a problem
> with the rate setting mechanism, but that would test it.
> 
> Larry


Hello,
it turns out that terms 'poor' or 'slow' performance on 8187b chipsets need to 
be discussed more in detail.
If I would have never had a faster network, I would possibly not notice those 
performance downturns.
I did some test on my notebook, once with mandriva 2010.0 and once with win 7.

The results:

windows:
 @ 2  meters distance
  rate : 54M
  dBm  : -46
  speedtest: 9.9/0.98 Mbit/s (down/up)
  DL file*: ~2.5 MByte/s

 @ 10  meters distance
  rate : 54M
  dBm  : -64
  speedtest: 9.9/0.97 Mbit/s (down/up)
  DL file*: ~1.25 MByte/s


linux:
 @ 2  meters distance
  rate : 36M
  dBm  : -30
  speedtest: 9.9/1.00 Mbit/s (down/up)
  DL file*: ~1.5 MByte/s
  tcpperf output: 11769623 b/s (11769.62 kb/s 11.77 Mbit/s)

 @ 10  meters distance
  rate : 18M
  dBm  : -45
  speedtest: 1.2/0.85 Mbit/s (down/up)
  Dl file*: ~130 KByte/s (<---!!)
  tcpperf output: 3663403 b/s (3663.40 kb/s 3.66 Mbit/s)

Dl file* = copy large file from a machine which is connected via 100mbit 
ethernet to the router.

I did all tests several times to make sure to not report some random results.

Before I used pid algorithm as someone described above, but could not notice 
any difference in network behavior.

If rate is set to auto, it _sometimes_ (~ twice a day) happens that connection 
is up and iwconfig shows a rate of 24M, but I can not even ping the router.
Same happens if I set a fixed rate of 36 or 18, but it happens more often 
(every 15 min) that the connection is up but no traffic is possible at all.
A fixed rate of 5.5M gives the most stable connection although the wireless 
speed is as slow @ 10 meters with auto rate (130 KByte/s is FAR from 5.5M)
The rate settings apply to 10 meters distance, which is my typical situation 
here at home.

On another PC with zw1211 wireless I set rate to 54M some time ago and there 
the trick did it, connection is perfect and very fast.