sundance-communications.com/forum Forums TDM Business Telephone Systems NEC Telephones & Systems DS1000 Dropped Calls

I work for a cable tv, internet, and phone provider in the New England region that just started offering business phone products to our commercial customers.

I've ran into a bit of a road block with dropped calls on a business customer of mine that just migrated over to us from Fairpoint (formally Verizon in these parts). Here's the skinny:

- 3 lines going into a NEC DS1000 phone system (sorry I don't have much more else other than the make/model)
- Arris TM504G cable modem
- Caller ID
- Call Forward on Busy is setup, with line 1 being the pilot number and 2, 3 being the overflow numbers.

Symptoms:

Intermittently a call coming into the pilot number will ring once, and then drop. To the customer it appears that the calling party had disconnected before they could answer the call but the calling party hears it ring once, dead air for a few seconds, and then drop.

What the modem sees when this happens is line one going off hook for one second, and then back to on hook.. Like a device is answering then hanging up right after that.

This also occurs if the inbound call is call forwarded to line 2.

We've narrowed it down to some sort of interaction happening between the phone system and our modem, but we have no idea what. Problem does not occur when phone system is bypassed.

This problem did not occur with previous provider so of course I get laughed at when I try to get any help from the customer's phone system vendor.

Any ideas?

Have you checked the Loop current of the "lines" coming out of the arris? I have seen them not being within the specs of real phone lines.

Caller ID might be a issue with the modem. If the phone system is setup for caller ID it has to collect the data from the in-coming call, this might be the time your equipment is disconnecting the call.

It's also come to my attention from a colleague at another clec that our MTAs only do loop start, whereas this phone system is only setup to do ground start.

Would loop start vs. ground start cause this sort of issue to occur?

The DS1000 is loop start

Well in speaking with the vendor that supplied the customer with the phone system he mentioned that the DS1000 can do loop start, but required an addon card to do so? If that makes any sense.

Nevermind, I got my terms mixed up here. Yea both the MTA and DS1000 are doing loop start.

I agree with DANS post above regarding loop current. Also, what is the ring voltage being provided? I've often seen ring voltage on these kind of lines not being within spec.

Most of the problems with ringing and cable modems are related to the ring voltage waveform. Many of the cable telephony modems use a "trapezoidal" ring voltage, as opposed to a traditional "sinusoidal" ring voltage. As far as I know, the DS1000 was designed to accept a sinusoidal ring voltage. I looked briefly at the specifications for the Arris TM504G , and there is mention of trapezoidal vs. sinusoidal ring voltage waveform types. "Configuration options for loop current, loop voltage management, and ringing waveform are available for each line interface." I would check the configuration of the TM504G, and try changing the ringing waveform type to "sinusoidal" and see if this clears the problem.

MTA is putting out ~45v during ring.