estimating VoIP data traffic size from VoIP signaling traffic size ?

Sun Oct 23 18:36:28 UTC 2005

      On Sun, 23 Oct 2005, John Todd wrote:
    > The media stats in SIP BYE signalling Bill Woodcock mentioned in his
    > message (jitter, packets, loss, latency, etc.) are only available in a few
    > end devices at the moment, notably Cisco.

Ah, that's right, I'd forgotten that, sorry.  On INOC-DBA we have a 
preponderance of Cisco phones, so one end or the other (all that's 
necessary) of most calls is a Cisco, and I tend to not worry too much 
about whether the remainder are a statistically similar subset of the 
total.

    > I think the best way to do this would be to graph the signalling volumes
    > and the media volumes over a week or two, and then build assumption charts
    > for future use.

Agreed.

    > If you're really a masochist, or you can't see the
    > media for architecture reasons,  you could write an extension to ethereal
    > or ettercap or a similar network monitoring and packet analysis tool which
    > unfolded each signalling message, extracted the codec descriptors, and
    > calculated flows.  You'd then have to keep state on each call, etc.

It's not quite that bad...  You don't need to keep state, you just need to 
know how much signalling is associated with each call, on average.  If you 
know the average amount of signalling per call for your traffic mix (which 
can be calculated from a baseline analysis of the signalling alone), the 
total amount of signalling, and the ratio of codecs in use (which can be 
a sample rather than a full count), you should be able to get a pretty 
accurate estimate, without ever tracking on a per-call basis.

                                -Bill