Hello All,

Over the summer we've installed brand-new network wiring throughout the school, complete with new HP switches and a new VoIP phone system. We're using an Asterisk-based iQ PBX 2000 device - basically an Asterisk setup in-a-box, with the idea being that we just plug it in and away it goes. The PBX comes with various interface cards, one of which is a BRI card to allow us to connect our two ISDN 2e lines, giving us a total of 4 external phone lines.

This should all be standard, easy-to-use stuff - this setup is probably the same as dozens of others installed every month with no problems. However, we're getting intermittent poor quality on incoming and outgoing calls. Sometimes you phone someone, or they'll phone in, and you'll hardly be able to hear what they are saying. The effect is best described as "buzzing" or "crackling" - as you or the other party speaks their words are pretty much obscured by fuzzy noise. It sounds rather like you might expect audio to sound if it was really badly encoded, or encoded at a really low bit rate.

Anyone any ideas as to what might be causing this? The problem seems to only happen with external calls, internal calls are fine, so we doubt it's the network setup. The network is brand-new, complete with a 10GbE fibre backbone and HP 2920 PoE-capable switches. There doesn't seem to be any pattern in the poor quality calls by way of type of number called (sometimes a mobile number, sometimes not), time of day or number of active calls at the time. We've tried two entirely new controllers and interface cards with the same effect. Most external calls are fine, it's maybe 1 in 20 that's poor.