VoIP Compatibility Issues with Phone Systems

Last updated Dec 7, 2011

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here are known problems with using automated phone systems on phone lines that are connected via the Internet. These are known as VoIP lines (Voice over Internet) and they deliver your phone conversations as digital data over broadband. If you are using a phone line via cable or DSL then you have a VoIP line.

In order to use standard telephones the data needs to be converted from digital to analog with a modem adapter. These adapters are usually supplied by your cable or phone company.

What Is a VoIP Modem Adapter?

This is the device that gives you the connectivity from your phone or phone system to the Internet. It converts the analog phone signals to digital so that the data can be sent over the Internet.

Some carriers, such as Vonage®, supply a VoIP adapter that connects to your Internet modem. While others supply a single unit that IS your modem with a telephony VoIP adapter built in.

If you have VoIP service direct from your cable company, you most likely will get a single unit... a modem with the telephone adapter built in. These are known as telephony modems. They have the usual Ethernet Jack to connect to your computer. And they also have one or two phone jacks.

VoIP Related Problems

Automated phone systems may encounter problems when connected to VoIP adapters that are not compatible. Common VoIP problems are... VoIP related problems are not the fault of your automated equipment. Your VoIP adapter may not be using standard BelCore signaling, or it may be interfering in some way.

The following equipment may encounter VoIP problems...  

Known Compatible VoIP Modem Adapters

You need to have a compatible adapter or telephony modem to avoid VoIP issues. We have had success with several modem adapters that are known to be compatible. These ring with the normal 20 Hz signal at 60 VAC, so inbound calls will be detected. They also provide the standard 48 Volts DC on idle lines, so an available outside line will be properly detected.

The following is a list of modem adapters that we tested and passed... Note: The Motorola Model ONT100DGJ4 causes a chirp sound at the start of a call. But this can be avoided with special programming.

Incompatible VoIP Modem Adapters

We have discovered problems when the VoicePro is connected to the following devices and therefore they are not supported... We cannot support the VoicePro when used with any of the devices proven to cause problems. Ask your cable provider to give you one of the compatible modem adapters that we tested (shown in the first list above).

If you wish to try the VoicePro with an untested modem that is not listed above, we will be glad to give you a 100% refund if the unit is returned within 30 days.

Incompatible VoIP Services

The following VoIP Telephone services are not compatible with the VoicePro and cannot be supported...

Solution for users of Cablevision Optonline®

Make sure you have the Cisco Model DPC2203C broadband modem, which Cablevision is using now. This has been personally tested by us and found to be compatible with the VoicePro.

Software Programming Solutions

  1. If you have trouble detecting incoming calls, ask your VoIP provider if they can program their adapter to provide a normal 20 Hz ring signal.
  2. If you have trouble seizing an outside line to make calls, ask if they can set it to provide 48 Volts DC.

BelCore Standards

At the least, check that your VoIP adapter is following these standards...

Standard Loop current

The line loop current is -48 Volts DC.

Standard Ring Signal

The standard ring signal is 75 Volts AC.

The AC waveform in the U.S. is 20 HZ and in Europe it's 25 Hz.

The VoicePro is a Class B device as per FCC Part 15 rules and therefore will respond to ringing frequencies between 17 and 68 Hz with the proper cadence.

The timing of ringing and pauses between rings, called cadence, is typically two seconds on and four seconds off in the US.