[VoiceOps] AT&T Cellular - DTMF

Adam Vocks Adam.Vocks at cticomputers.com
Wed Jul 15 11:24:51 EDT 2015

Finally Solved!


I want to thank everyone who help with advice and/or contacts on this


Here is an e-mail from AT&T about this problem.


Raghu and I have been working on this today - and we found that there
almost certainly exists a 'bug' in the EVC/Nortel MSC (VSE MSC) causing
this problem. This issue is being caused by any far end switch that
responds to an incoming call with the optional ISUP_CPG (Call Progress)
message that does not have the optional BCI parm included (Backwards
Call Indicators). If the EVC MSC routes a call to a PSTN trunk group and
sends an ISUP IAM to far end, far end sends ACM (Address Complete) and
if they also send an ISUP_CPG that does not contain the BCI parm - this
causes the MSC to reject any DTMF tone requests from the originating
callers. This exact same issue was found in our MSC during a FFA (First
Field Application) trial of the previous version of MSC software
(uCore5) back in late 2013. We believe that our newest MSC software
version (uCore15A) might be missing this bug fix and causing this
problem - AGAIN. I have a HIGH PRIORITY case opened up with the MSC
vendor that I will pursue with great diligence.


SO - for now - the only way to fix this is to change the routing to not
use this TYVLILXC50T02A1B trunk group. I will have more info on when we
can expect a fix from the vendor - but best case scenario for that would
be several WEEKS. 


I know this is NOT good news - BUT it is all I can offer up at this
time. Thanks -


We had them route around the problem switch and our problem went away.
We're using a Sangoma NSG SS7 gateway.


Thanks again everyone!




From: VoiceOps [mailto:voiceops-bounces at voiceops.org] On Behalf Of Adam
Sent: Wednesday, June 24, 2015 11:58 AM
To: voiceops at voiceops.org
Subject: [VoiceOps] AT&T Cellular - DTMF


I've got an odd problem that someone might be able to point me in the
right direction to get some help.


AT&T cellular customer calls a number destined to our LRN.  Customer
presses a digit on the phone, no DTMF audio ever comes across the trunk.
If that same customer calls a number with the same npa/nxx not destined
for our LRN, DTMF audio comes across the trunk.  These calls are coming
to us via SS7 trunks and the ILEC that these calls transit through has
verified that both calls come in on the same trunks, one has DTMF audio,
one does not.


This problem started on Thursday morning.  Prior to Thursday morning,
AT&T cellular calls were arriving to us via our FGD Tandem connection,
now they are arriving via the local rate center switch.


I've talked to AT&T and attempted to put in a ticket on the DS3 that
enters the ILEC, but they refused to do that because they said the DTMF
would be audio and they would just pass it through.


Anyone have advice?


AT&T (low level tech) states that the DTMF tones are generated at the
phone and are in the audio stream the entire way.  Does anyone know if
AT&T uses some sort out of band dtmf signaling?




Adam Vocks

CTI Fiber 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://puck.nether.net/pipermail/voiceops/attachments/20150715/f3ce51b9/attachment.html>

More information about the VoiceOps mailing list