Sporadic Dropping calls and voice cutting of any other word

Dear all,

We have this system setup in one of our customers:

PBX in a Flash Version = Running on HARDWARE
│ FreePBX Version = │
│ Running Asterisk Version = 1.4.42 │
│ Asterisk Source Version = 1.4.42 │
│ Dahdi Source Version = │
│ Libpri Source Version = 1.4.12 │
│ Addons Source Version = 1.4.13

We are using a Rhino R1T1 connected to a VoIP PRI from Verizon, the issue that is happening is that in the middle of the call or when they parked the call the call disconnect, checking the logs i notice that i’m getting a lot of cause 16:

Span 1: Channel 0/8 got hangup request, cause 16

as per this link:


This cause is due to unspecified cause.

Everything else since to be ok, i think that has to be something on the provider end, but i would like to be 100% sure that is in their end, We ran network lines to split the network and the phones and the issue still, also from time to time they are getting chopping/cutting any other word conversation.

I think that it may be something on Verizon end.

Any advise? thank you in advance.


I have/had the same issue on PBXIAF hardware with HP ML110 G6 + Digium PRI T122 and T121 on E1 link. This issue was noticed on at least 4 different installation so it cannot be telco problem.

I was getting very bad dahdi test using PBXIAF and after weeks of troubleshooting I eventually changed to Elastix.

I started getting excellent dahdi_test result and drops seem to be not happening any more. I am after changing second system to Elastix and will know if problem is resolved in next few days.

Don’t get me wrong, I am a big fan of PBXIAF and I use in tens of other places on pure sip infrastructures. However it looks like there is something not right when it comes to E1/T1 links which causes random drops.