[smokeping-users] How suited is Smokeping for VoIP purposes?

[Chris Wilson]

Hi Nik,

On Mon, 24 Oct 2011, Nik Mitev wrote:

> When I added same probe to two more hosts, jitter and delay appeared 
> (3-4ms) on all hosts for the 20ms probe. Thinking that it is an issue 
> where FPing handles the load badly, I added one more graph to a fourth 
> host and expected an increase in jitter, but it went away completely and 
> returned to the original state for all four hosts. I am able to 
> reproduce that. At the same time I had a parallel probe running which 
> only differed in the offset - it was completely unaffected and flat at 
> all times.

I think this is a bug with FPing. Smokeping relies on fping to do the 
actual pinging in the default configuration, although you can choose a 
different pinger. I remember trying to debug fping to solve a different 
bug and finding it trying, but if you program C or you can reproduce the 
problem on the fping command line, then it's possible to report 
upstream or investigate further.

> 2. Separate scaling issue follows from FPing being limited to sending 
> pings at 1ms interval as its highest speed. For the purposes of VoIP, 
> jitter needs to be measured on packets sent at 20ms intervals, which 
> limits the number of hosts we can monitor to 20 at a particular offset 
> and to 200 if we only monitor 10% of the time and split the hosts in 10 
> groups. Those numbers are the theoretical maximum and are likely to 
> actually be lower.

It's theoretically possible to make fping send any number of pings per 1ms 
interval, although further skewing the time-distribution of pings may 
exaggerate the effects of any network boundaries beyond what you'd 
experience in a real call.

Also beware that if you monitor continuously at this rate, your monitoring 
is going to have a major impact on network bandwidth use and thus 
negatively affect call quality.

Cheers, Chris.
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