Connecting to Other Systems

We know that you’re creative and we couldn’t hope to address every possible situation that you face, but armed with a little knowledge about how the Hx works internally, you should be successful with most applications.

In short, the Hx will operate on anything that electrically “looks" like a POTS telephone line, and you can connect it to anything that is designed to run a standard Analog telephone set.

It needs loop current of 15-120 ma at 12-50 volts to run its line interface chip. The chip provides telephone line audio and line signaling status (such as on-hook/off-hook/ringing/loop drop, etc.) to the processor to control the unit. If loop current isn’t present, you’ll have no audio and the Hx will simply hang up, which is the correct behavior.

Connecting to PBX's and VoIP Analog Terminal Adapters

When connecting to PBX station ports, VoIP Analog Terminal Adapters (ATA's), and even telephone company-provided “pair gain” systems and channel banks, sometimes things can be a little different.

Odd voltages, strange feature implementations, and other issues can cause problems with audio performance and produce weird behavior. Fortunately, these kinds of interfaces keep getting better, meaning that the Hx will probably “just work” - with a few possible exceptions.

The most common issue is likely to be what we call "disconnect supervision": That is, “What the line does when the caller on the line hangs up”. Disconnect supervision is especially important if you intend to use the auto-answer feature. When an “on-air” connected call drops, a wide range of things may happen:

• Most PBX’s will simply drop the audio from the outside line and perhaps send a fast busy (or reorder) tone; the Hx will stay off-hook until you manually drop it unless you’ve set the Call Progress Tone Disconnect to disconnect after hearing reorder tone with the internal dip switches.

• Some PBX’s will send a momentary loop current interruption that will cause the Hx to release from the line, which is the desired behavior (Congratulations! You’re a winner!); we’ve had good luck with PBX’s from Avaya (Larger systems).

• EON/Cortelco, NEC, and station disconnect supervision can be enabled in Mitel digital PBX’s, though it is not set this way by default; most telephone company central office lines do support Calling Party Control (CPC) or loop current interruption-based disconnect.

• Most ATA’s used by VoIP providers will simply play a reorder (fast busy) tone; most are capable of sending the CPC loop current interruption signal, though many have this feature disabled by default; it can usually be turned on through the web interface on the unit; the best ones we’ve seen are units made by Cisco/Linksys and Sipura.

• Some Foreign Exchange or ‘choke’ lines will not pass the CPC signal and the line will go silent, to dial tone, a reorder, or even a recorded message; this is mainly a function of circuit design and the selection of central office equipment by the telephone company.

Connecting to a Telos Direct Interface Module

Using the Hx - or any hybrid supporting disconnect supervision with the Direct Interface Module (DIM) - requires an external source of loop current. The DIM provides only a “dry” transformer audio feed which worked well with the simpler hybrids of the time. Visit the Telos website or contact support for several options that will allow you to use the Hx with the DIM.

Connecting to....?

Telos Alliance collects and shares what we learn about “real world” telephony with our customers, who come up with creative ways to use our products and often create elegant solutions for unusual problems. If you need help connecting to a system not covered here, please reach out to our support team.

Likewise, we’d appreciate hearing about your successes and challenges to share with other colleagues and friends. We’re also interested in your experiences with service providers and telecom systems and equipment vendors.