perfSONAR User Q&A and Other Discussion

[Piotr Pikusa <>]

Hi Ralph!

Ralph Niederberger wrote:
> I should respecify my question a little better to be more accurate. 
> Within the CISCO web pages:
>    
> http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a008009496e.shtml 
>
>    "How To Calculate Bandwidth Utilization Using SNMP"
>
> I have to calculate the utilization using several requests via SNMP. 
> In principle it is:
> "number of packets coming in/out per interval" divided by  
> intervall-period
>
> They provide a percentage value, so they multiply by 100 and divide by 
> interface speed.
>
> Since the sql tables within perfSONAR SQL-MA have a field valueUnits 
> "Bps". I assume I have to
> store here the packets (not bits) transfered (in or out) per second. 
> So to compute those values,
> I have to  start two snmp  requests, ie. at start-time and end-time of 
> measurement intervall.
> It would be much more convenient to store the Interface counters (in 
> or out) only.
> A client application could then calculate the utilization itself 
> getting all the counters within the intervall
> interested in. It would also allow calculating utilization for any 
> time intervall, not only the once
> measured, since the snmp interface values are updated by default in 
> the machine to which I send
> my request.

Since you have valueUnits field in SQL-MA base, you can store values in 
any units you want. Bps is only an example.
This approach is free from hardware specifications and scalable. Network 
user choose what unit is the best for him.
Of course you can use counters in constant time and make your own unit.


> > > Further is the direction of traffic defined by the metadataId, e.g. 
> > > by specifying
> > > metaid-interface-in and metaid-interface-out?
> > >     
> I assume that there are different metadata ids for input and output 
> measurements, since file
> ....
> has a field <nmwgt:direction>in</nmwgt:direction>
> is that correct? Or means utilization always  input+output? But then 
> the perfsonarUI tool could
> not differeentiate between input and output.

There are different metadata ids for input and output.

> > > And what do I have to store in the db field "value"? Is it the 
> > > utilization
> > > of the interface, which means before inserting data I have to 
> > > calculate this
> > > dependend on the last time I stored a value (packets in since last 
> > > inserting
> > > devided by time since last inserting?
> > > Or do I have to store the packet count of the interface only and when
> > > requesting infos, the utilization will be calculated dependend on 
> > > the time
> > > interval I specify within the client request?
> > >     
> see same discussion above.
> I assume valueUnits "Bps" in SQL perfsonar_utilization table means 
> "Byte per second", not "bit per second".
> Is this correct?

One more time. You store some values in value filed in units specified 
in valueUnits. You send information to SQL-MA, that on 21 of July at 
14:30, utulisation in "in" direction was 5 Mbps. Or more general data 
per time. So yes, you should calculate it yourself. But if you check it 
every second (what is standard approach) and your unit in unitValue is 
based on seconds, you don't have to calculate anything. This is 
advantage of perfSONAR system - you can store any values in any units, 
it doesn't force anything.
When you want to use perfsonarUI to work with data you store, you should 
use data per second units (not packets per second) because it transforms 
these units to Mb/s. You can also use % unit option in perfsonarUI 
Summary - it is based on capacity of the interface.

> > > many thanks in advance
> > >
> > > Ralp


Thank you for interesting questions.

Regards
Piotr Pikusa