VL-88                    June 2013

Who's that Knocking at My Door? (over IP)

By William Flanagan, Publisher

Almost 20 years ago we chose a digital phone system, in part, because it offered "door boxes" that acted as door bells and speaker phones.  When visitors ring, we can speak with them from any phone on the system. But we can't see them.  The ability to see a visitor is a major incentive to update a door phone.

Even back then it wasn't completely simple:  the door box was analog and needed a converter to appear as a trunk on the digital key set.  As proprietary devices, and analog, they integrated easily; voice and power shared the same wire pair.  Sitting outside, somewhat protected from the weather, the door phones have worked solidly to this day.  So has the digital PBX/KSU.

So here's almost a confession from a writer on VoIP--I don't have a VoIP system (though I have used VoIP previously).  One reason to stick with the digital PBX was the lack, for many years, of affordable "VoIP" door boxes.  A few voice-only models existed, but were bulky, pricy, and needed individual a.c. power. Keeping the original analog boxes in a new VoIP system would require a media gateway for each:  another expense, more hardware to manage, and probably a software integration task.  Not exactly KISS.

In Living Color

Looking around the market recently, a very different landscape appeared.  There are dozens of VoIP door boxes and similar wall-mounted products.  They range from the simple (one button, voice only) to very complex (dozens of buttons, multiple video cameras, and door release relays as well as audio). Some mount easily on the wall surface, others embed securely. One vendor alone has 50 configurations.

Video is a major benefit of the move to IP.  While you can still get audio-only boxes, most models include at least one video camera. Video over IP is easier than analog over coax cable.  Some video boxes stream H.264 to provide constant monitoring and can multicast the signal to any number of receivers.  LEDs on the box ensure adequate illumination in any weather and at all times of day.

Analog boxes draw their power over the single pair that carry the voice path.  VoIP needs two pair for Ethernet, but Power over Enet is available for most designs.  So you may need a 'newer' switch with PoE injection, or a separate mid-span injector, to avoid the wall transformer.  At least any existing structured wiring installation will continue to support the door-box function.

Optional Features

Voice codecs: G.711/PCM voice integrates easily with most VoIP systems and SIP (version 2 typically) phones.  H.323 is also offered.  You can get echo cancellation on full-duplex voice connections.

Buttons:  Multi-tenant buildings can share one box with multi-button models and modular extension boxes for additional buttons.  A button should be for ringing only;  voice activated transmission or full-duplex connections eliminate the need for the visitor to "push to talk."  For easier reading of labels, buttons may be back-lit.

Door control:  Dry contact relay (or two) operates a lock (via DTMF input).  Might be used for a light.

Power:  PoE (802.11af), or d.c. from a wall brick.

Answer point:  You answer the ring at a trunk or extension appearance on a hardware phone or a dedicated softphone app on a PC or smartphone.  Several vendors offer apps for smartphones and tablets so you can answer the door from anywhere.

Ethernet:  Most are standard 10 and 100 Mbit/s on up to 100 m of cable.  A few offer extended range with PoE to 300 m.

Displays:  The door box can include an LCD window to offer information, tenant lists, menus, and images.

Weather resistance:  Most models are designed for exterior locations, made of aluminum and plastic, but they may not be designed for full exposure to storms.  One vendor offers an optional weather-tight enclosure.

Management:  An IP device is a computer, so you need to manage it.  Web interface is common; other systems are available.

Prices:  Basic one-button boxes without video start at $88 to $150.  Top of the line could be armored (vandal resistant), made of corrosion proof stainless steel, with lots of buttons, or sophisticated in-wall mounted at $1500 to over $3000 each.

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