I think this is very implementation specific. Obviously, a 100% packet loss duration will make you unable to hear anything, but dropping the call is quite another story.

I'm at home right now, and I have a Lingo VoIP router. I disconnected a network cable for 30 seconds and the phone call was still going when I reconnected the cable (I tested this calling our local ski report recording).

I'd recommend testing this yourself - just disconnect a network cable and see what happens (of course, you'll need to disconnect a cable that doesn't signal the VoIP hardware/software it needs to reset, and doesn't do any long-running DHCP retraining or anything).

If your packet loss is being caused by a piece of hardware on your own network that is signaling your VoIP system that it needs to "retrain", then I can imagine any length of outage would drop calls (as short as 1/2 second? sure). One example of this might be if you unplug the network cable of your VoIP hardware itself. It's going to want to re initialize the network card, re query the DHCP server, and who-knows-what-else to get things going again. That would probably cause a call to be dropped.

In most conditions, though, 1.5 seconds of dropped packets is *WAY* *WAY* too short to drop a call for.

You'd need to talk to your VoIP hardware / software vendor to get concrete answers about dropping calls vs total packet loss periods.

- Pete