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Contact Centre issues in SIP


We  have changed from ISDN to SIP and we are using CUCM 8.6. We are also  running contact centre with uccx. After the switch over the contact  centre are reporting many issues. some of the issues are :

   --> Call comes and no one is there.

   --> Call dropped out whilst on hold.

   --> Unable to transfer. Caller dropped out.

   --> Phone rang tried to answer, but it had engaged signal.

   --> Phone rand engaged signal no sound.

We are also running maximum session of 20 in transcoding on CUBE router.

dspfarm profile 1 transcode 

description --- Transcoding Resources ---

codec g729r8

codec g711ulaw

codec g711alaw

codec g729ar8

codec g729abr8

maximum sessions 20

associate application SCCP

However  when I checked the router for number of active RTP connection it was  going till 27 and 28. Would increasing the maximum sessions to 40 will  resolve some of the issues above?

I am not sure why these issues are coming and what should be done to resolve it. Any help would be much appreciated.


Contact Centre issues in SIP

This is a huge discussion, because it sounds like your design, or perhaps a lack of a design, is what causing your issues.

To address two of the larger items when talking about UCCX and SIP: codec and DTMF relay:


UCCX can only support one codec at a time.  Which codec do you have it configured for right now?

What codecs does your ITSP support and furthermore, what codecs are you willing to support on your SIP Trunk to the PSTN?

Then look at traffic patterns and determine if have the two the same or different makes more sense.  For example, if 80% of your calls into UCCX are from the PSTN, then having UCCX setup for the PSTN preferred codec makes more sense, because you require less transcoders.

DTMF Relay

Next, what DTMF relay is supported by your PSTN SIP Trunk?  Most of the time this is going to be RTP-NTE aka RFC2833 aka Inband aka RTP Payload Type 101 (yes, there's many names for this).

UCCX can only support one kind of DTMF, albeit a broad one, and that's called Out of Band DTMF.  This is because it is a CTI connection to CUCM registering SCCP CTI Ports.

With a missmatch on DTMF relay, you are going to need an MTP.  Do you currently use the CUCM software MTPs?  Do you use IOS Software MTPs?  Do you have them available in the right codec(s)?

There's a bigger thing to consider here and that's understanding your design, and having a good design that was founded in sound decision making.  Once you do that, you may find out that your problems go away on their own, because a well designed solution shouldn't be having these kinds of problems.

I do speak from first hand experience, as I run UCCX in my environment with centralized PSTN SIP trunking and it works.

I hope these two items get you started looking in the right direction.  Don't just through more resources at the problem, try to understand it.  Good luck.

Anthony Holloway

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Anthony Holloway

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