David,

Thanks for the information. You've highlighted all the network attributes that have an effect on network quality insofar as VoIP is concerned.

I think it isn't enough to simply measure bandwidth, latency, jitter and loss, however. You'll end up with a bunch of numbers that may seem meaningless unless put into some sort of context. The proper context is, I believe, whether or not degradation in these attributes will adversely affect a typical voice conversation. For example, mobile phones often suffer from some degree of loss, but fortunately, the human brain is pretty good at filling in the gaps and often will not notice the degradation. It is therefore difficult to say that, for instance, a one percent loss of packets is unacceptable. Another example is whether or not compression is performed on the voice channel. In this case, a compressed packet contains a lot more information, so while a single dropped packet of uncompressed voice may be acceptable, a similar drop of a compressed packet may not.

To address this fairly subjective environment, a number of tests have been developed that can quantify the subjective quality of a VoIP connection. Generally, these tests reveal the level of frustration a human will experience during periods of degradation. The MOS scale (Mean Opinion Score) is one such vehicle for making that measurement. The letter "O" in MOS stands for "Opinion", which can be quantified based on the actual opinions of people when subjected to the adverse effects of a network.

The bottom line is that while network degradation can be measured based on jitter, loss, bandwidth and latency, it is not always easy to say to what degree it will effect a VoIP conversation. And even if they do effect a conversation, it's not easy to determine the degree of devastation. Further, you cannot rely on your provider to make this assessment for you, as he may only be looking at loss, jitter, etc. and not at how the combination of degradations affect your VoIP experience.

You can get more information at http://www.ixiacom.com/library/white_papers/display?skey=voip_quality. This white paper explains how VoIP call quality can be assessed using methods that quantify human subjective scoring to ascertain network VoIP readiness.

Thanks again!

Dan

Thanks for this great post. I recently discovered Solicall which offers call monitoring and voice quality improvement for VoIP systems. Worth checking