Unknown number ringback issue appears to be related to transfers

Rhino Ceros (3U box)
3 pots lines plugged into 1,2,3
Hunt group from carrier is set to ring 1,2,3 BNF carrier VM

This is a persistent issue, sometimes happening upto 70 times a day. I have been onsite twice and when I am there it doesn’t do it - much. I’ve seen it a couple of times.

This is what I gather is going on, it may not be completely accurate. This is the best I have ATM.

The receptionist gets a call coming in CID is “unknown” - she answers and there’s dialtone, sometimes there maybe a ringing and the PBX will play a message like - the call can not be completed press 0 for the operator (I’ve not heard the message so I cant confirm.) Whether she answers or not, about 10-15secs later the process repeats, this may happen several times. I am not told this happens when she transfers the call.

Call flow-
Time condition - business hours
Business hours yes - announcement
Business hrs no - IVR

Announcement plays -> Ringgroup A
Ringgroup A -> Ringgroup B
Ringgroup B -> IVR

any ideas?

I think I may open a ticket with Rhino - maybe it’s a hangup detect issue with the TDM

I may also create a VPN to the PBX and add a phone to the ring group and see if I can see it myself (though that’s a lot of work, if there is a simple solution)

I contact Rhino

They said sounds like a D-Bounce issue (not sure what that is), but possibly inaccurate flash-hook was being setup off by carrier services on the POTS (making them not so P) e.g. 3Way calling, Call waiting.

I called the carrier, and disconnected those services.

We’ll see tomorrow

Once I started disconnecting services from the analog lines, the customer remembered that “oh yea, our old voicemail would ringback notifying us of the voicemail.” The old voicemail service on the analog line was calling back into the PBX, whenever it got a voicemail, and kept calling back until they were checked.

Disconnected the VM service - no more unknown callers.