Some incoming calls do a short ring and then cut out.

[Narcio]

I've been using a Cisco SPA112-1.3.2-XU(014) ATA with freephoneline.ca for a few months now.

Most calls both incoming and outgoing work fine. If I use my cell phone I can call my freephoneline number and it rings and works fine. If I place a call from the freephoneline number out to my cell phone or other local numbers it works fine.

However, there seem to be some incoming calls that will not connect properly. This is what happens:
Caller ID lights up and briefly shows the number and then a partial ring comes through, about half of the length of a normal ring, then the call is disconnected / lost.

I have found that my fiance's work phone always does this when she tries to call. From her end, she says she tries to call my home number on freephoneline, she hears complete silence and then it disconnects, giving her rapid beeping of the sort that suggests your call was disconnected. The time it rings is too short to actually pick up the phone so I've never been able to try picking it up before its already disconnected. If she then immediately calls me back from her cell phone, the call will come through to freephoneline, ringing my phone normally and the call works fine.

I also notice that this happens from an 866 Bell Canada phone number (yes, they keep calling trying to spam me since I recently cancelled my Bell home phone.) When this 866 Bell number calls me the same thing seems to happen from my end. I see the Caller ID on my phone light up and show Bell and the number, it then gives about a half of a ring and then the call is disconnected before I can pick up the phone.

There are a few other places that have the same problem when trying to call in to my system including at least one doctor's office, although others can call and connect to me just fine.

Other normal local calls to home numbers seem to all work fine, both incoming and outgoing.

The calls that don't work for me seems to be consistent. Ie, the same particular numbers always have the problem, and the other numbers never have this problem, which leads me to believe it has something to do with those particular numbers trying to call. I am not completely confident, but I suspect this may be an issue related to other incoming phone system being a voip system or a complex business phone system. I know my fiance's work phone is all run through some voip system, and the big Bell call centre calling me is probably also using some sort of complex system.

I don't think this has anything to do with port forwarding, or my internet router, etc, because most calls both in and out work just fine, as long as its to a simple phone and not a big company's phone system, etc.

Can anyone give any advice / trouble shooting suggestions for this issue?

I can make some screen shots of my Cisco ATA's settings etc, if needed. I have put in all of the settings that freephonline.ca provided to me when I bought the SIP unlock key. I also roughly followed the following guide for enabling NAT settings and using a STUN server, sicne I'm behind a NAT router: http://blog.voipdiy.com/2013/07/configu ... -with.html