I am a computer scientist and I'm working as sysadmin of a small firm where I've been managing also the telephone system that my predecessor put in place.

Albeit I don't really have the skill set for doing this, until now it was enough.

Since the last few months however we are experiencing a strange phenomenon on one of our lines: after a couple of minutes of use (but not every time) the audio quality suddenly deteriorates and the outside party cannot hear us unless we talk very loudly. This usually happens on inbound calls.

A brief description of our setup: we have two dual-channel isdn land lines with two different operators over which we also have an adsl internet line each.

The first operator gives us two POTS numbers on its line and these work perfectly both inbound and outbound.

The second operator instead gives us an ip telephone number on its line and this is the one we are having problems with.

Now, I know what you are thinking, the ip setup is obviously rubbish. Well, I'm quite expert in network administration and I'm relatively sure that it isn't. The line works as it should and the operator confirms it.

Still, while answering calls from the ip lines my users laments poor quality of audio every other day. I admit that I didn't believe them at first (I've been unable to reproduce the fact myself) but the accounts were too many and they came from independent sources, some of which are highly trusted and unlikely to prank the poor, overworked sysadmin.

So, here's the question for you engineering types: give me a way for me to automatically test a phone line audio quality without having to subject myself to listening in to all the calls of some of my users for a couple of days or two (which would badly impact my already too full todo list).

What I'm hoping for is a way for me to use my android phone to call the ip line and without having to wait for it get a warning the moment the audio quality drops, so that I can draw some reliable statistics on how often this happens and I can demonstrated to the operator technicians that I'm not wasting their time (like they more or less explicitly told me last time I called for help on this).

I hope I'm asking this in the right community. If not, have my apologies and please point me to the right one.

  • \$\begingroup\$ Can you clarify your setup here: ISDN2 lines are not POTS and you cannot run ADSL over ISDN2 or the other way round. It sounds like your issue is with a VoIP service over an ISDN2 data link over copper, yes? \$\endgroup\$
    – John U
    Commented Jan 15, 2015 at 15:45
  • \$\begingroup\$ Also a few basics of fault finding: Does it happen in both directions? Does the IP link drop or record errors? Does the ISDN/ADSL link drop or record errors? Do other services on the same link drop/slow/error? \$\endgroup\$
    – John U
    Commented Jan 15, 2015 at 15:54
  • \$\begingroup\$ Last I looked, proper ISDN testers are quite expensive while ADSL testers give almost no additional info over what you can read in the logs of your router. \$\endgroup\$
    – John U
    Commented Jan 15, 2015 at 16:19
  • \$\begingroup\$ Additional question: Are your phones analogue (POTS) or ISDN/PABX style ones, and is there a PABX or other converter/server in the system? \$\endgroup\$
    – John U
    Commented Jan 15, 2015 at 16:33
  • \$\begingroup\$ What type of phone system did your predecessor put in place? Is it something like a Mitel, Avaya or Cisco? In my experience with Mitel systems upgrading firmware and confirming phone set compatibility with the ICP switch has resolved phantom issues. Beyond that I would ask for a certified system provider for support. \$\endgroup\$
    – Tinkerer
    Commented Jan 15, 2015 at 16:37

1 Answer 1


Pretty much every major (and minor) vendor of network testing hardware has products for something called VOIP (quality) (passive) monitoring/analytics or thereabout. These compute aggregate statistics on the quality of the conversations, among other things. These usually don't run from your cell phone, but from a specialized routing/testing device. There's an ITU standard for VOIP passive monitoring called P.563 (this is the recommendation number) and also called 3SQM (the name of the algorithm), but it is not (yet) widely used by testing equipment manufacturers, and has been the subject of some criticism, e.g. [1][2]. So it's a bit of a wild west out there with respect to product features etc. for passive monitoring of VOIP quality.

I'm not endorsing any of these products, but here some examples:

You might be able to find some free software that does something similar, although you'd still need trunk-router-grade hardware to run it on. I was only able to turn up some 3SQM non-free software, which requires conversations to have been recorded by other means. There is a free piece of software called http://sourceforge.net/projects/voipmonitor/ but this does not do conversation-level quality analysis, but only testing for bulk suitability of the IP link to carry VOIP (ITU G.107). But you can probably at least use it to record conversations.

ITU has also put out a VOIP active conversation quality testing standard called PESQ and this is widely used by (active) testing products, but these inject a reference signal at one end and you don't seem to want that.

So the above generally covers "give me a way for me to automatically test a phone line audio quality". However, for your specific problem "the audio quality suddenly deteriorates and the outside party cannot hear us unless we talk very loudly", the issue may not even be (automatically) testable only from your side... If the packets leave your site unmolested but get messed up (volume-wise) by your provider/carrier or by some of their peers (probably not all), there would no way to establish that by just looking at packets on your end. You'd have to record/monitor the conversation from the other end to apply 3SQM to it.

My experience with cheap VOIP providers is that when they have (intermittent) quality problems the contracts/SLAs are harder to enforce than they are to terminate.


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