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

G.W. Haywood ged at jubileegroup.co.uk
Wed Oct 26 09:35:31 CEST 2011

Hi there,

On Mon, 24 Oct 2011, Nik Mitev wrote:

> I did a fair amount of experimenting and research ... what I found
> in relation to Smokeping created a couple of questions.
> 1. Some of the results produced seem to be inconsistent with the
> state of the network and parallel probes disagree with each other.
> ... iptables ...  When I added same probe to two more hosts, jitter
> and delay appeared ... I added one more graph to a fourth host and
> expected an increase in jitter, but it went away completely ...
> returned to the original state for all four hosts. ... 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.

It's really great to see someone doing some careful work.  I'm afraid
I can't offer much more than encouragement.  It would be great too if
I could attempt to repeat what you've done, but other than our small
office LAN I've never had a network which would be capable of doing
such things.  I've used VoIP quite a bit but it's been more a matter
of getting something which would permit some sort of communication
than providing what you might consider an acceptable service to more
than a handful of users.

I can at least say that I'm not a bit surprised by the things you're
describing.  When you start to make careful measurements you'll find
all sorts of things crawl out of the woodwork.  There's a tremendous
amount of software in e.g. the network stacks, iptables is perhaps a
crude tool for this sort of work and you haven't given us much else to
go on.  Which operating systems do you use?  On what hardware are they
running?  Apart from running Smokeping, what else are they doing?  Can
you describe the network for us?  Is it entirely under your control?
What continuous data throughput rate(s) can it sustain?  How many hops
are there between endpoints?  What are the switches and routers?  Are
they doing any kind of traffic shaping?  What are the typical round
trip times?  Have you reduced the network to a bare minimum set of
harware and repeated the tests?  Some time ago I had buggy hardware
issues which limited the round trip times given by 'ping' to integer
multiples of 4ms - have you checked that the interval timers in the
smokeping machines are reliable?  Have you attempted to use something
like Wireshark to monitor all the traffic on the network?  Have you
tried inserting a router in the packet path which does nothing other
than time the packets?  Are you running ntp on all machines involved
so that you can make (more or less:) absolute time measurements?

> 2. Separate scaling issue follows from FPing being limited to sending
> pings at 1ms interval

There will always be some limit, what's the question? :)

> I am new to the list and not sure if I can attach the config files and
> images to the email - I will of course email them to anyone who might be
> interested.

Perhaps you can put them on one of the file sharing sites and post a link
so that those who are interested can grab them at will.



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