Maximizing 802.11b throuput

Bichot Guillaume (Princeton) guillaume.bichot at
Thu Mar 13 10:18:16 EST 2003

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
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

-----Original Message-----
From: André Luiz Ribeiro Moutinho [mailto:andre.moutinho at] 
Sent: Thursday, March 13, 2003 8:25 AM
To: hostap at
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 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. 

Thanks a lot, 

Andre Moutinho 

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