perfSONAR User Q&A and Other Discussion

[Alan Whinery <>]

Dan,

You can't have both:
>> 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.

and

> Sorry, without the ability to see below 1 mS, there is no such thing
>> as "a general sense of campus network performance".

Sorry, but I get value value from analyzing packet loss exclusively,
which probably points out the same queuing-related problems that I
assume you're looking for with latency.

And assailing the perfSONAR project's foci is a little like writing your
congressman, it has ceremonial flair, little value otherwise.

What I would be very interested in are:

        "An Exposition Of The Joys Of Short Path Latency Analysis"
        and
        "How To Implement PTP Timing In An Academic Enterprise Network  
        For OWAMP Discipline"

or existing links.

Because I think that pretty much nobody is on the same page as you are,
but coming from you, it intrigues us, because you say smart stuff, and
there's much implicit "exercise for the reader" in your in-band comments
that I've seen.

-Alan


On 2/19/2016 8:40 AM, Magorian, Daniel F. wrote:
> Actually, surprise!  Smart SFP TWAMP reflectors (that also can sniff
> packets for remote pcap and other useful things) are $300/ea, only
> about 2x what the small nodes cost, and the central initiator that
> times the TWAMP reflectors is also cheap.  As an SFP it's also super
> easy to replace ordinary SFPs with.  I bought the two dozen and the
> traffic initiator for < $5k, chump change.
> 
>> small-footprint nodes can be deployed all over campus, to give us a
>> general sense of network performance
> 
> Sorry, without the ability to see below 1 mS, there is no such thing
> as "a general sense of campus network performance".  Either you can
> resolve your campus path latency, or you just have lines along the
> bottom of your graphs at 1 mS, pretty worthless.
> 
> Why settle for low resolution when you can have high for close to the
> same cost?
> 
> Dan
> -----Original Message-----
> From: Peter Gutierrez 
> [mailto:]
>  
> Sent: Friday, February 19, 2016 1:13 PM
> To: Magorian, Daniel F.; 
> ;
>  
> 
> Cc: Andrew Gallo; 
> ;
>  Jason Zurawski
> Subject: Re: [perfsonar-user] feedback on PTP
> 
> 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
> 
> 
> 
>