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Is VoIP Jitter, Delay and Packet Loss the Best Measure of Voice Quality?

By Yossi Zadah, VP One Voice Operation Center Business Line, AudioCodes

"One of the values that I think men in particular have to pass on is the value of empathy. Not sympathy, empathy. And what that means is standing in somebody else’s shoes, being able to look through their eyes.” Barack Obama

Empathy – being able to feel sorry for someone else’s troubles – is a basic ingredient for good mental health. However, sometimes, when irony is involved, empathy might turn to ambivalence.  For example, you will naturally feel empathy when you see or hear about a house going up in flames, but you might even crack a smile if the house in question is the fire department. (Of course that would happen only if no one was injured, right?)

We recently had voice quality issues in our corporate telephony system. Now that might happen in any organization, but when it happens in AudioCodes, the company which has become the hallmark of HD VoIP, that’s ironic.

Our IT guys brought their usual armour to battle and started taking on the packet loss with Wireshark (network protocol analyser), upgrading this and downgrading that.  Then they started looking at the AudioCodes products on the VoIP network; scrutinizing the latest IP phone firmware, restarting the SBCs, disconnecting the MGW.  And still, they couldn’t find anything to help pinpoint the problem.

After a week or so, one of my colleagues placed a call and couldn’t stand the noise on the line.  Naturally, he cut short the call as cellular SP has “trained” us to do over the past two decades. And since he is the Product Manager for AudioCodes Management Solutions, he decided to try troubleshooting the problem on his own (15 years in R&D can come handy sometimes), using the AudioCodes Session Experience Manager.

Now I have to apologize up front since at this stage the story gets a little corny.  He found that a substantial amount of the off-net calls originated by the UC system were faulty with a poor quality score.  After conducting a short analysis with our IT department, he found a misconfiguration of the VMware machine running one of the IPPBX servers.  He wondered why our own IT guys weren’t using the AudioCodes Session Experience Manager. Could it be as a famous man once said, “familiarity breeds contempt”?

I am not relating this story to point shortcomings on the part of our IT department (God forbid!) or alternatively to glorify an AudioCodes product.  A vendor who speaks about his own products is almost as bad as a mother who talks about her own children.  My point, rather, is to elaborate on the concept of VoIP quality monitoring.

It is human nature to reach a conclusion by reviewing the consequences of actions. The human brain is constantly on an endless quest to solve riddles and reach conclusions (Gestalt psychology or Gestaltism).  Therefore, it’s perfectly normal for an IT engineer to analyse the VoIP network, search for the causes of poor quality such as packet loss, jitter and delay and based on the analysis, evaluate the call quality.

From my perspective, this analysis method is problematic.  It’s like commenting on the taste of a casserole by evaluating its ingredients – before even cooking the dish. Voice quality can’t be accurately evaluated by reviewing only the relevant network impairments (jitter, delay and packet loss). An accurate measure of voice quality needs to be taken at the VoIP edges (MGWs, SBCs, IP phones, soft clients) while taking into account the vocoder, jitter buffer type and depth (static, adaptive), packet loss metric (Network Packet Loss Rate, Jitter Buffer Discard Rate) and more. This information can’t be obtained by only analysing the traffic.

Epilogue

There is a mistaken belief in the industry that VoIP Quality Monitoring applications are like insurance policies -you buy them hoping not to use them. This belief is due to decades of trusted legacy telephony and basic trust in the organizational network, devices and solutions. In Reality, VoIP Quality Monitoring should be considered for ongoing use for the following:

  • Day-to-day, end-to-end quality monitoring and assurance operations with the ability to perform proactive actions to prevent quality issues
  • Root cause analysis for diagnostics when VQ issues arise

So if you are having VoIP quality issues, I empathize, even though after reading this, you might smile at the irony.



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