Maximizing 802.11b throuput
Dave.Edwards at abicom-international.com
Thu Mar 13 10:30:16 EST 2003
You also need to factor in the card's io performance. For the pccard
based prism2 devices this can be as long as 200uS to write a frame into
the device. I'm not sure if it's an issue with the PCI based devices but
be aware, the pccard (16bit) interface is painfully slow!
This can be a problem if you are implementing a polling protocol with
Also, some versions of the Prism 2 firmware will only send multicast
frames after a beacon. The AP firmware will allow multicast frames to be
sent at other times, but it's difficult getting a legal copy of it!
Bichot Guillaume (Princeton) wrote:
> In theory the overal bit rate would be not so far from 11 Mbits. If
> I'm not wrong, based on payload size of 1500 bytes, a total overhead
> of 1148 bytes max (including PHY (guard interval + 1Mbit/s overhead) ,
> MAC (DFIS + data frame header), LLC header, SNAP header , IP header,
> UDP header) would give you a total throughput of 7.8 Mbit/s.
> This is for one way streaming in multicast/broadcast without any
> IEEE802.11 association attempt (no uplink traffic at all) and good
> channel quality.
> In multicast however I've constated that the bit rate is sometime
> limited by the firmware of my card (PCI prism2 Linksys). I cannot
> stream more than 1Mbit/s.
> If you stream in unicast this is another story. MAC acknowledgment may
> reduce considerably the bandwidth depending on the quality of your
> channel. Practically the 3Mbit/s number seems often raised.
> In theory transmitting in multicast with the maximum packet size is
> the way to maximize the bandwidth usage. However you have to cope in
> some way with error correction.
> Guillaume Bichot
> As of February 12th, 2003 Thomson unified its email addresses on a
> worldwide basis. Please note my new email address:
> guillaume.bichot at thomson.net http://www.thomson.net/
> -----Original Message-----
> From: André Luiz Ribeiro Moutinho
> [mailto:andre.moutinho at compsisnet.com.br]
> Sent: Thursday, March 13, 2003 8:25 AM
> To: hostap at shmoo.com
> Cc: Mauricio Micoski; Marcelo Ferreira Vinhas; Marco Antônio Fernandes
> Subject: Maximizing 802.11b throuput
> 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
> 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
> trying to optimize the transmitted data block size.
> I need to use the maximum data bandwith available in order to
> the maximum mount of video sessions possible.
> Thanks a lot,
> Andre Moutinho
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