perfSONAR User Q&A and Other Discussion

[Peter Gutierrez <>]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On 02/19/2016 12:43 PM, Magorian, Daniel F. wrote:
> Dan and Jason, this discussion on PTP pretty much misses the point
> entirely,


In my opinion, accurate intra-campus latency measurement has value, but I
don't expect it from a cigarette-box server any more than I expect them to
provide 100Gbps interfaces for bandwidth testing. As long as these
low-cost, low-power, small-footprint nodes can be deployed all over
campus, to give us a general sense of network performance, it's a yoooge win
.

Deploying expensive, pizza-box servers with appropriate hardware to do
more advanced latency/bandwidth measurements in the places I need it is a
worthwhile investment as well.

PeterG

> 
> https://www.perfsonar.net/deploy/timekeeping-with-ntp/
> 
> and demonstrates how software guys rarely see the need for/advantages
> of dedicated hardware.  Follow that logic to its conclusion and you can
> do away with small nodes altogether, and just create a centralized VM
> box with virtual measurement node instances cabled to wherever.  Or
> containers these days, which at least are lighter weight.
> 
> Obviously no one thinks that *synchronizing* PTP is cost-effective yet,
> as would be needed for OWAMP.
> 
> The point you're missing is that TWAMP, while it does traverse the path
> twice, goes and comes back to the same PTP initiator.  Therefore it has
> no need to sync to anything else, and is accurate internally to ~1 uS
> so intra-campus paths can be measured.
> 
> Since you're showing no interest in measuring such intra-campus paths,
> you need to stop saying "perfsonar world domination" and change it to
> "perfsonar inter-campus WAN world domination".  And if that's your
> mission and the scope of the project, software NTP-based timing to mS
> works fine.
> 
> Just know that you're making the project unusable for an enormous new
> intra-campus market, due to WAN-oriented bias.
> 
> Dan in his talk today said  something like  "Well, anything below 1 mS
> is basically instantaneous" .  Again, spoken with a strong WAN bias and
> little understanding of intra-campus paths.  If your north-south
> core-to-edge campus traffic is talking 1000 uS, you have serious
> performance issues that really need to be looked into and probably have
> users beating you up daily.  Which normally everyone blames on
> firewalls and repeats that tired litancy without bothering to actually
> measure, because they can't without the right tools.
> 
> In reality good Cisco or Palo Alto campus firewalls introduce ~ 50 -
> 100 uS latency when working properly, as does your IPS.  I know,
> because I measure ours and watch for latency spikes on the cacti
> graphs.
> 
> My overall point is, you could extend Perfsonar's usability to
> intra-campus path measurement relatively easily with some architectural
> changes, but nobody wants to because of WAN bias.
> 
> Sigh.
> 
> Dan Magorian
> 


- -- 
Peter Gutierrez
Network Analyst
Lederle Graduate Research Center Lowrise A147
University of Massachusetts Amherst
740 N Pleasant St
Amherst MA 01003-9306

 PGP: 0xE1668A41
413-545-1606
A: Because it interrupts the logical flow of discourse
Q: Why is top posting bad?
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iEYEARECAAYFAlbHWyAACgkQPTwtHOFmikFsfQCgiWB6uRuJgsDf901izoS+buA3
zz8An0k2tiV717xSmCAC0bbHAg5kGfqa
=YYmd
-----END PGP SIGNATURE-----