Re: [Iperf-users] Reported Bandwidth

[Metod K. <met...@lu...>]

Howdy!

When there are two limiting factors when sending data:

    * bandwidth of first leg
    * bandwidth of slowest leg

Sender application (iperf) can sense bandwidth of first leg as sending 
IP stack will buffer certain amount of data (Tx buffer) and then 
throttle back the application. In your case it seems that sending 
computer's WiFi can transmit at roughly 3Mbps. If that was the overall 
bottleneck, receiver wouldn't see any dropped datagrams (or nearly any 
of them).

Overall bottleneck (it could be the last leg as well) will impose 
dropped datagrams when testing UDP and that will be seen only by 
receiving IP stack / application.

Peace!
  Mkx

-- perl -e 'print $i=pack(c5,(41*2),sqrt(7056),(unpack(c,H)-2),oct(115),10);'
-- echo 16i[q]sa[ln0=aln100%Pln100/snlbx]sbA0D4D465452snlb xq | dc

------------------------------------------------------------------------

BOFH excuse #9:

doppler effect



Randy Buck je dne 23/03/10 21:46 napisal-a:
> Hi all,
>
> I am using Iperf to find the optimal sending rate of my wireless mesh 
> network.  I am running into an issue when I run the following command:
>
> iperf -u -fk -c 5.0.0.1 *-b 5000K* -p 4000 -t 10
>
> I get the following report (or something very similar).  I've bolded 
> parts in question:
>
> ------------------------------
> ------------------------------
> Client connecting to 5.0.0.1, UDP port 4000
> Sending 1470 byte datagrams
> UDP buffer size:   109 KByte (default)
> ------------------------------------------------------------
> [  3] local 5.0.0.24 port 58708 connected with 5.0.0.1 port 4000
> [  3]  0.0-10.2 sec  *3623 KBytes*  2916 Kbits/sec
> [  3] Sent 2524 datagrams
> [  3] Server Report:
> [  3]  0.0-10.4 sec  *2703 KBytes*  2128 Kbits/sec  26.951 ms  640/ 
> 2523 (25%)
> [  3]  0.0-10.4 sec  1 datagrams received out-of-order
>
> Why is it that when I start the client and specify -b 5000K that I am 
> sending at a rate much less (3623 KBytes)?  Shouldn't Iperf send out 
> UDP packets as fast as it can?  I can understand that the acutal 
> bandwidth is much less (2703 KBytes) considering I lost 25% of the 
> packets.  Please explain to me why Iperf is not trying to send out at 
> 5000 KBytes.  How is the number 3263 KBytes calculated?
>
> Thanks,
>
> Randy Buck