Re: [Madwifi-users] Fw:Re: [Madwifi-users] WG311 - reporting succes

[Yvan G. <yva...@la...>]

Hi Michael,

I understand why my calculation was a bit too direct !
Just forgot that TCP/IP is over radio signal ....
Tks for answering
Yvan

> On Fri, Oct 24, 2003 at 06:18:13PM +0200, Yvan Garnier wrote:
> > Hi Michael,
> > I connect the WG311 to an AP WG602 ( both can do 11b and 11g )
> > 11g mode is force on both, so tell me if I'm wrong but 54Mbps => 6,4Mo/s
> > ( theoric of course )
>
> No, not even in theory - you forgot about the MAC protocol which dictates
> "some" overhead for preamble, header, inter frame spacing, acknowledge
> packets, and (when using 11g) additional packets that ensure 11b
> compatibility.
>
> Have a look at
> www.atheros.com/pt/atheros_range_whitepaper.pdf
>
> When looking at TCP with 1500 byte packets, you get:
>
> For 11g with 11b compatibility enabled: 14.4Mbit/s = 1.8MByte/s
>
> For "11g only mode" or 11a: 24.4Mbit/s = 3MByte/s
>
> Note that you should only turn off 11b-compatibility if you can be sure
that
> there are no other 11b devices within your receive range, because
otherwise,
> your throughput will degrade even more due to collisions caused by 11b
> stations transmitting because they don't know that a 11g transfer is in
> progress.
>
> www4.ncsu.edu/~jjun/index_files/full_tmt.pdf
> has a bit more detailt about the protocol and the calculation of
theoretical
> throughput - note that when bridging frames to a wired ethernet, you are
> limited to about 1500 bytes frame size.
>
> cu
> Michael
>