ndt-users list created

[Richard Carlson <>]

Scott;

The current link detection algorithm uses packet pair timings of the TCP 
and ACK streams.  It forks a small libpcap routine off to handle this 
task.  The idea is that TCP will normally send bursts of packets out rather 
than try to pace them out at a nominal rate.  The timings are then 
quantized into a small number of bins, and I assume that fractional links 
or bonded links don't exist so 300 Mbps would be reported as an OC-12 link 
(100 < 300 < 622).

One of the things I found while creating this algorithm is that the libpcap 
routine mis-reports the Server Data Link speed.  The timestamps that 
libpcap uses are placed on the packet as they are processed by the 
CPU.  When the server is sending data (the Server Data case) the timestamps 
actually record the time the packet is handed off to the NIC, not the time 
the NIC puts the packet on the link.  So the routine is really measuring 
the memory or I/O bus speed, not the network speed.  To get a 10 Gig report 
the bus must be running over OC-48 speeds. What kind of server is 
this?  Did previous versions of the NDT report other values?

I'm not sure if this is a bug or a feature in the libpcap routines, but 
there isn't much I can do without another time source.

The interesting question to me is why the Client Data link says 
FastEthernet.  Did this really negotiate to GigE speeds?  What was the 
reported throughput?  Is the connection send/receive buffer limited?

One last thing, the /usr/local/ndt/web100srv.log file contains 4 lines like 
this
spds[0] = '  0 4 120 1 74 349 39 0 0 1 0 4 59.72' max=349 [59.35%]
spds[1] = '  0 1 125 1 24 175 8 0 0 0 1 1 59.57' max=175 [52.40%]
spds[2] = '  0 4 164 127 424 33 90 98 989 35 0 4 6.17' max=989 [50.36%]
spds[3] = '  0 3 161 28 308 224 61 12 35 4 21 122 17.58' max=308 [36.84%]

These are the counters for the 4 cases listed below.  Could you post this 
data to this list, I would like to see what the distribution is.

Regards;
Rich Carlson

At 10:11 AM 10/29/2004 -0400, Scott Fringer wrote:
> Hello,
>   I've just upgraded our local NDT server to version 3.0.22.  It is
> connected to a 1 Gbps Ethernet port (10/100/1000 copper connect on a
> Cisco 6509.  Both ends set to auto-negotiate). When tests are run
> against the box it reports the link is 10 GigE:
>
> Client Data reports link is 'FastE', Client Acks report link is 'FastE'
> Server Data reports link is '10 Gig', Server Acks report link is 'FastE'
>
>   Any ideas what might be causing this, or if there is anything I can do
> to correct this?
>
> Thanks,
>   Scott
>
> --
> Scott Fringer                              Shands Healthcare @ U.F.
> Technical Analyst II                       Gainesville, FL