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Community Member

CCM 5.1 to Siemens ISDX-S over QSIG


We have a new CCM 5.1 install which is connected to our legacy PBX system, which is a Siemens ISDX-S (actually formerly a Mercury PBX, but Siemens now support it). We're using two QSIG links to connect the two together.

Most things are working, but in some circumstances, calls are getting through, but are silent when they are connected. Basically, if somebody external dials a DDI for example, the call will enter the PBX (via a DASS link), then be routed out over the QSIG to the gateways. Then then gets to the phone on the IP network, which rings. The phone is answered, but neither end can hear or speak to the other. The line is for all intents and purposes, dead. It will stay 'connected' until one or other party hangs up.

This mostly happens with calls from external to DDIs on the VoIP side, and occasionally from internal PBX users to the phones on the IP side. Calls between IP phones however, are faultless, and calls OUT of the IP system are also fine, either to PBX extensions, or external numbers; external calls to the PSTN are routed over an ISDN30/E1 which is directly connected to one of the gateways. This happens randomly to. Sometimes it works, sometimes it doesn't.

Has anybody else any experience of connecting up the two systems? I've been in touch with Siemens, but they're not really turning up much info, as not many people are connecting up ISDX systems to CCM. Most are using Hipath PBXs.

Any advice gratefully received!!


Re: CCM 5.1 to Siemens ISDX-S over QSIG

I know this isn't exactly the same but i had the issue on a Callmanager 4.1 connected via Qsig trunks to a Siemens DX.In between were some westell boxes doing the DPNSS to QSIG conversion.

Occasionally we would get the same issue.

I added the voice rtp send-rcv command and also made sure that the mgcp bind commands were set.

Haven't had any reports of any issues since,



Community Member

Re: CCM 5.1 to Siemens ISDX-S over QSIG

I did see mention of that, but we found something else.

We have done some more testing since, and found that the top end channels (17-30) don't work! We isolated them, and tested them all one by one, and got silent calls. Lower channels work fine. So it seems it's either an oddity at the CCM gateway end, OR, something wrong on the DX, or possibly even a hardware issue one end or the other.

When we find a solution, I'll post back!

Community Member

Re: CCM 5.1 to Siemens ISDX-S over QSIG

A fix!

Well, we think.

It seems that the ISDX likes to use a continuous channel map, rather than the default (Use Number When 1). Changing it to Continuous, suddenly makes the channels above 15 work. It seems the CCM end was going out on one channel, and the ISDX was treating it as another. Hence no working!

And now it does. There's a few other niggles, and we need to test it more, but so far so good.

Hope this helps somebody!

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