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New Cisco quality scores



Just when you were getting a handle on knowing what MOS (mean opinion score) or it’s cousin MLQK (MOS Listening Quality K-factor – the last 8 seconds MOS) means and how they’re useful, Cisco is phasing them out.

Why are they being dropped?

Well, there are many reasons, but the two primary ones are that

  • MOS is codec dependent so is hard or impossible to compare across codecs
  • it also doesn’t scale properly between calls of different durations so can’t be used to reliably compare those either.

What good is a metric that you can’t use in comparisons?

What are the replacements?

All Cisco IP phones now support a few new metrics around “call concealment time”.

IP based conversations (via IP phones of a variety of sorts) are subject to lost packets, out of order data, and indeed all sorts of generally minor and unavoidable problems. When this happens the devices “fill in” the missing voice information with made up audio. These losses that are “filled in” are called “concealed” time, and the new statistics measure those losses and its effect on voice quality.

“Made-up audio” sounds like it should always be a problem, but the fact is that small amounts of missing data can be filled in very effectively and without any real degradation of the conversation. It’s the longer periods that are the problem.

So without further ado, here’s the new metrics

Concealed Seconds (CS)

A measurement of how many seconds showed some concealment during a call. “Some” in this case being at a level where it probably wasn’t hard to understand the speaker. These are useful to know are happening, but aren’t generally a problem.

Severely Concealed Seconds (SCS)

Similar to Concealed Seconds only measuring seconds where the speech was probably very hard to understand. Cisco defines this as seconds where the concealment that second was greater than 50 milliseconds or approximately 5 percent. SCS are seconds that are probably problems.

Severely Concealed Seconds Ratio (SCSR) and Concealed Seconds Ratio (CSR)

If you take the number of Concealed Seconds (CS) or Severely Concealed Seconds (SCS) and divide it by the duration of the call, you get a ratio or percentage.  This gives us a way to compare any codec, any call duration, any sort of devices – the scale is always the same, it’s simple to calculate, and it is a good proxy for “I couldn’t hear what you said there”.

What is generally considered a bad call?

As with most answers, it depends.

First, know these are just the defaults Cisco uses – they are adjustable.

Second, it really does sort of depend on the length of the call.  If you have a really short call – say leaving a short voicemail with a name and telephone number – it doesn’t take a lot of SCS to make a high SCSR, and that makes sense because it only takes a second or two and suddenly the call was useless. “This is ~~~ch at ~158~~7420, call me back!”. Maybe you’ll guess from context or from the part of the number you heard, but who knows?

If you have a longer call, well, a small amount of concealment can be dealt with easily enough. “Sorry, you were garbled there for a second, what was your number again?”

So the guidelines Cisco uses are:

  • For call durations under 20 seconds
    • Good is under 3% SCSR
    • Acceptable is between 3% and 7% SCSR
    • Poor is anything over 7%
  • For call durations over 20 seconds
    • Good is under 20% SCSR
    • Acceptable is between 20% and 30% SCSR
    • Poor is anything over 30%.

How do we see our SCS/SCSR

Easy!

Grab your field picker and search for any of the above fields.  Add them in by clicking the green “->” arrow, then drag them around on the right side to put them where you want in the column list.

Once you have it there, it’ll follow you from Browse Calls to General report and back again. It’ll also be searchable like anything else using the “search filters” field in Browse Calls.




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