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<TITLE>RE: Maximizing 802.11b throuput</TITLE>
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<P><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> You also need to factor in the card's io performance. For the pccard </FONT>
<BR><FONT SIZE=2>> based prism2 devices this can be as long as 200uS to write a </FONT>
<BR><FONT SIZE=2>> frame into </FONT>
<BR><FONT SIZE=2>> the device. I'm not sure if it's an issue with the PCI based </FONT>
<BR><FONT SIZE=2>> devices but </FONT>
<BR><FONT SIZE=2>> be aware, the pccard (16bit) interface is painfully slow!</FONT>
</P>
<P><FONT SIZE=2>To be exact it should add delay but should not reduce the throughput (16bits PCMCIA = 20 Mbytes/s). </FONT>
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<P><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> This can be a problem if you are implementing a polling protocol with </FONT>
<BR><FONT SIZE=2>> the radios.</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> Also, some versions of the Prism 2 firmware will only send multicast </FONT>
<BR><FONT SIZE=2>> frames after a beacon. The AP firmware will allow multicast </FONT>
<BR><FONT SIZE=2>> frames to be </FONT>
<BR><FONT SIZE=2>> sent at other times, but it's difficult getting a legal copy of it!</FONT>
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<P><FONT SIZE=2>That is true. This implies big limitatino as I have constated with my card.</FONT>
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<P><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> Bichot Guillaume (Princeton) wrote:</FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> > In theory the overal bit rate would be not so far from 11 Mbits. If</FONT>
<BR><FONT SIZE=2>> > I'm not wrong, based on payload size of 1500 bytes, a total </FONT>
<BR><FONT SIZE=2>> overhead </FONT>
<BR><FONT SIZE=2>> > of 1148 bytes max (including PHY (guard interval + 1Mbit/s </FONT>
<BR><FONT SIZE=2>> overhead) , </FONT>
<BR><FONT SIZE=2>> > MAC (DFIS + data frame header), LLC header, SNAP header , </FONT>
<BR><FONT SIZE=2>> IP header, </FONT>
<BR><FONT SIZE=2>> > UDP header) would give you a total throughput of 7.8 Mbit/s.</FONT>
<BR><FONT SIZE=2>> > This is for one way streaming in multicast/broadcast without any </FONT>
<BR><FONT SIZE=2>> > IEEE802.11 association attempt (no uplink traffic at all) and good </FONT>
<BR><FONT SIZE=2>> > channel quality.</FONT>
<BR><FONT SIZE=2>> > </FONT>
<BR><FONT SIZE=2>> > In multicast however I've constated that the bit rate is sometime</FONT>
<BR><FONT SIZE=2>> > limited by the firmware of my card (PCI prism2 Linksys). I cannot </FONT>
<BR><FONT SIZE=2>> > stream more than 1Mbit/s. </FONT>
<BR><FONT SIZE=2>> > </FONT>
<BR><FONT SIZE=2>> > If you stream in unicast this is another story. MAC </FONT>
<BR><FONT SIZE=2>> acknowledgment may</FONT>
<BR><FONT SIZE=2>> > reduce considerably the bandwidth depending on the quality of your </FONT>
<BR><FONT SIZE=2>> > channel. Practically the 3Mbit/s number seems often raised.</FONT>
<BR><FONT SIZE=2>> > </FONT>
<BR><FONT SIZE=2>> > In theory transmitting in multicast with the maximum packet size is</FONT>
<BR><FONT SIZE=2>> > the way to maximize the bandwidth usage. However you have </FONT>
<BR><FONT SIZE=2>> to cope in </FONT>
<BR><FONT SIZE=2>> > some way with error correction.</FONT>
<BR><FONT SIZE=2>> > </FONT>
<BR><FONT SIZE=2>> > Guillaume Bichot</FONT>
<BR><FONT SIZE=2>> > </FONT>
<BR><FONT SIZE=2>> ----------------------------------------------------------------------</FONT>
<BR><FONT SIZE=2>> > ----------</FONT>
<BR><FONT SIZE=2>> > As of February 12th, 2003 Thomson unified its email addresses on a </FONT>
<BR><FONT SIZE=2>> > worldwide basis. Please note my new email address: </FONT>
<BR><FONT SIZE=2>> > guillaume.bichot@thomson.net <A HREF="http://www.thomson.net/" TARGET="_blank">http://www.thomson.net/</A></FONT>
<BR><FONT SIZE=2>> ></FONT>
<BR><FONT SIZE=2>> > </FONT>
<BR><FONT SIZE=2>-------------------------------------------------------------------------------- </FONT>
<BR><FONT SIZE=2>As of February 12th, 2003 Thomson unified its email addresses on a worldwide basis. </FONT>
<BR><FONT SIZE=2>Please note my new email address: guillaume.bichot@thomson.net </FONT>
</P>
<P><FONT SIZE=2><A HREF="http://www.thomson.net/" TARGET="_blank">http://www.thomson.net/</A> </FONT>
</P>
<P><FONT SIZE=2>----Original Message-----</FONT>
<BR><FONT SIZE=2>> > From: André Luiz Ribeiro Moutinho</FONT>
<BR><FONT SIZE=2>> > [<A HREF="mailto:andre.moutinho@compsisnet.com.br">mailto:andre.moutinho@compsisnet.com.br</A>]</FONT>
<BR><FONT SIZE=2>> > Sent: Thursday, March 13, 2003 8:25 AM</FONT>
<BR><FONT SIZE=2>> > To: hostap@shmoo.com</FONT>
<BR><FONT SIZE=2>> > Cc: Mauricio Micoski; Marcelo Ferreira Vinhas; Marco </FONT>
<BR><FONT SIZE=2>> Antônio Fernandes</FONT>
<BR><FONT SIZE=2>> > Subject: Maximizing 802.11b throuput</FONT>
<BR><FONT SIZE=2>> ></FONT>
<BR><FONT SIZE=2>> > Hi,</FONT>
<BR><FONT SIZE=2>> ></FONT>
<BR><FONT SIZE=2>> > I am implementing a realtime video streamming application using</FONT>
<BR><FONT SIZE=2>> > 802.11b in order to transmit video data.</FONT>
<BR><FONT SIZE=2>> > Transmitting MJPEG 320x240@30fps and 40% quality results a</FONT>
<BR><FONT SIZE=2>> > 3Mbit/s total bandwith. When I try to increase the video data</FONT>
<BR><FONT SIZE=2>> > bandwith (for instance, rising JPEG quality), the radio channel</FONT>
<BR><FONT SIZE=2>> > starts</FONT>
<BR><FONT SIZE=2>> > failing to transmit all video information. I would like </FONT>
<BR><FONT SIZE=2>> to know what</FONT>
<BR><FONT SIZE=2>> > is the REAL 802.11 data transmittion throuput (4 or </FONT>
<BR><FONT SIZE=2>> 5Mbit/s ??) and</FONT>
<BR><FONT SIZE=2>> > what could be done in order to maximize the data throuput. For</FONT>
<BR><FONT SIZE=2>> > instance,</FONT>
<BR><FONT SIZE=2>> > trying to optimize the transmitted data block size.</FONT>
<BR><FONT SIZE=2>> > I need to use the maximum data bandwith available in order to</FONT>
<BR><FONT SIZE=2>> > transmit</FONT>
<BR><FONT SIZE=2>> > the maximum mount of video sessions possible.</FONT>
<BR><FONT SIZE=2>> ></FONT>
<BR><FONT SIZE=2>> > Thanks a lot,</FONT>
<BR><FONT SIZE=2>> ></FONT>
<BR><FONT SIZE=2>> > Andre Moutinho</FONT>
<BR><FONT SIZE=2>> ></FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> </FONT>
<BR><FONT SIZE=2>> </FONT>
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