atcomsystems.ca/forum Forums TDM Business Telephone Systems NEC Telephones & Systems Tandem calls don't always work

I have an SV8500 in my "Central office" and an IPS 2000 in one of my remote offices. The two are connected over CCIS via a point-to-point T1 provided by telco. All trunking is done by the 8500 otherwise.

Outgoing calls from the 2000 supposed to go to the 8500 via the ccis and then to telco via a PRI.

The 8500 have no problems whatsoever. All its stations can call out local, long-dist and international. They can also call the ips and all its stations no problems.

However, calls from the ips have some problems. You can call all sta in the 8500, you can make local and you can make long-dist calls, but international calls always fail with fast busy.

LCR access code on the 8500 is "1". It gets stripped every time a call is sent to local or long distance carriers.

On the ips, the lcr access code is also "1", and its not stripped when the call is sent to the 8500, so in theory the 8500 should just handle it as a call from any of its stations. But somehow it does not. It always rejects international calls.

Monitoring trunks and routes shows that international calls from the ips do grab a trunk in the ccis to reach the 8500, but not sure what happens then. An ISMC trace on the 8500 of such call coming from the ips does show all digits arriving to the 8500, including the "1" access code. But then again, ISMC has no detailed documentation. I can barely make out from the Hex garble the calling station number of the ips, and the called number.

I'm not even sure if the problem is with the 8500 or the ips...

Anybody has a clue?

In the 2000 does 200>1>a129? Try making 8a5xxx>157>00.

Yes, 200>1 is a129. I tried the 8a5xxx>157 but didn't make any difference.

I played around with trunk class conversion (CM4220...) and it does affect calls, but still couldn't enable international calls. Unfortunately the two sites are about 6 miles apart, and so I can only play with one at a time. I was on the IPS site yesterday, and I'm more and more convinced that it's actually the 8500 that needs attention.

Well, today, I'll play with that. But still need help if anybody has any ideas.

Problem solved. I needed to change a setting:
CMA710>0>15 to CMA710>0>14. It's a timer on the CCIS channel and gives more time for the IPS2000 to wait for an ACM signal (whatever that is) to come back from the SV8500 once the dialed digits were sent. Basically, on international calls, you can't specify the exact amount of maximum digits dialed by CM85, since the number of digits vary country-by-country.

So when you finished dialing, the IPS waits a certain amount of time before it thinks dialing is complete and starts processing the call. When it sends the digits to the 8500, it does the same thing: waits for a certain amount before it starts processing the call. I assume, that's the point when it sends back an ACM signal to the IPS (it must be some sort of acknowledge signal). It appears the problem was that the IPS didn't wait long enough for the ACM signal coming back from the 8500 before it said "well, looks like nobody cares on the other end that I'm trying to send out a call, so I give up" and gave fast busy for the caller even before the 8500 had a chance to look at the digits sent to it by the IPS.

So when I increased the wait time from 15 sec to 28 sec, that was enough, and calls started to go through.

All this, I decoded from the ISMC command of the 8500 monitoring messages for successful domestic calls and unsuccessful international calls, and doing a search for "ACM" on the IPS Command Manual.

Thanks for all your helps.