RES: Maximizing 802.11b throuput

[André Luiz Ribeiro Moutinho]

I am using two linux machines running 802.11b orinoco in Ad-Hoc mode.
Each one is connect to a convencional Ethernet card as follows:

0----------------0<-------------->0-------------------0
Sender          router1  wvlan  router2              receiver

Concerning video compression. I believe that it should be better, 
and cheaper, to use a bttv video grab in order to capture video data.
I believe that I should need to compress the JPEG frame and compress it
again
by software into MPEG4. The main reason of using such a JPEG card is the
lack of 
processing power. But if you know any MPEG4 encoder card !!!

Another question: I am new to 802.11b and the first time I setup a wireless
link using Linux and 802.11b I did it very fast. The second time I spent
some time
trying to figure out why It was not working. Finally I discovery IWCONFIG
tools and 
some parameters (e.g. key, mode,...) that I had to set. Do you know why
these
parameters changes each time I startup the computer ?? I was forced to apply
the iwconfig
each time I startup the computer.

Thanks,

Andre

-----Mensagem original-----
De: Ray [mailto:ray at sonictech.net] 
Enviada em: quinta-feira, 13 de mar?o de 2003 17:11
Para: hostap at shmoo.com
Assunto: Re: Maximizing 802.11b throuput


On Thu, Mar 13, 2003 at 10:24:44AM -0300, Andr? Luiz Ribeiro Moutinho wrote:
> Hi,
> 
> I am implementing a realtime video streamming application using 
> 802.11b in order to transmit video data. Transmitting MJPEG 
> 320x240 at 30fps and 40% quality results a 3Mbit/s total bandwith. When I 
> try to increase the video data bandwith (for instance, rising JPEG 
> quality), the radio channel starts failing to transmit all video 
> information. I would like to know what is the REAL 802.11 data 
> transmittion throuput (4 or 5Mbit/s ??) and what could be done in 
> order to maximize the data throuput. For instance, trying to optimize 
> the transmitted data block size. I need to use the maximum data 
> bandwith available in order to transmit the maximum mount of video 
> sessions possible.

What is your network like, client -> HostAP -> client or something else? 
I'm getting 4 - 4.5 Mbps (as shown by ncftp) going from a computer on my
wired lan to a wireless node via a hostap machine (in AP mode) at the
moment.  My hostap machine is pretty underpowered so there might be a little
room for improvement in my setup.  I was going to suggest setting rts to off
as long as you arn't dealing with any hidden node problems but I just tried
it and it made no difference at all (which suggests something must be wrong
imho).

BTW, I've got a hardware mjpeg capture card and now you've got me curious so
I'll probably try playing live video over my link this weekend if I have
time.  Another option, if you have the cpu for it would be to recompress to
mpeg4 which should be pretty good at half or less the bandwidth of mjpeg.

-- 
Ray
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