Re: Transfer vs. Bandwidth

[Stephen Hemminger <shemminger --at-- osdl.org>]

On Tue, 16 Nov 2004 16:02:54 -0500
Jason Hammerschmidt <JHammerschmidt --at-- metroland.com> wrote:

> Greetings,
> 
>   Couldn't find this answer so I'm posting to the mailing list.  Can anyone
> explain how a Transfer of 96.0MBytes over 10.0 seconds equates to
> 80.4Mbits/sec?  My math 96Mbytes * 8 bits per byte / 10 seconds = 76.8Mbps,
> close but not exactly the same as the reported output from iperf (see
> below).  I'm running iperf 1.7.0 pthreads on Mac OS X 10.3.3
> 
> iperf -c 172.16.155.74
> ------------------------------------------------------------
> Client connecting to 172.16.155.74, TCP port 5001
> TCP window size: 65.0 KByte (default)
> ----------------------------------------------------
> [  3] local 10.150.0.89 port 50722 connected with 172.16.155.74 port 5001
> [ ID] Interval       Transfer     Bandwidth
> [  3]  0.0-10.0 sec  96.0 MBytes  80.4 Mbits/sec

The confusion arises because iperf is following the common usage and
converting the definition of "mega" when going from measurement of
storage to communication.

MBytes for space are measured Mega  = 1024*1024
rates are measured with mega = 1000000

8 * 96 * 1024 * 1024 = 805306368 bits

http://en.wikipedia.org/wiki/Megabyte