Trends in Technology: Voice over IP in Broadcast Studios


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POTS lines are still the most common and present the most performance challenges. A POTS line uses a two-wire loop that carries DC for off/on hook signaling, 90VAC ringing current, tones for caller ID transmission, call set up, and call progress, and of course speech audio. By its nature, it has loop loss and a fairly complex characteristic impedance, making separation of the transmit and receive audio much more complex and difficult.

Beyond copper

In the current competitive environment, telephone companies are largely ignoring the copper outside the facility that carries POTS lines to your door in favor of selling more exotic and profitable cable-TV-like services. You’ve probably noticed more scratchy, hummy, lossy lines and, more importantly, noticed the now-lengthy repair commitment times, sometimes stretching weeks-long.

If we were designing a telephone service for broadcasters from scratch, we would likely specify that it have the following properties:

  • A four-wire path; that is, separate transmit and audio paths
  • Fast signaling on a separate path
  • More control over transmission and routing
  • Provisions for carriage of voice, video and any kind of data we could imagine
  • It would be dirt cheap

    VoIP delivers all of these features today; we just have to do things a little differently than in the past to make use of it.

    It’s completely possible to run VoIP within your own facility and across your own network while still using legacy methods for PSTN connection. You’d be making a mistake by not investigating and taking advantage of some of the new PSTN connection paths and their very aggressive pricing, but you don’t have to make that move yet.

    I suggest you connect using multiple methods until you’re comfortable with a particular strategy. The value of multiple providers and redundant paths in emergency situations also shouldn’t be ignored.

    At the 2011 NAB Show, Comrex introduced the STAC VIP, its IP-based phone system.

    At the 2011 NAB Show, Comrex introduced the STAC VIP, its IP-based phone system.


    In the past, many decisions about phone systems were made because of the phone instruments themselves. People decided on a system because of the look, the feature set or the cost of the phone sets. But now that the system lock in is gone – the requirement to use products from a single vendor – you can choose the end point type based on your facilities’ needs and wants without limitations.

    End points are telephones, soft phones (computer apps) and appliances. They are what you talk into, and what you hang up. Our company, Telos Systems, has created end points that address the unique requirements of on-air use, including an entire multi-line on-air system (The Telos VX). Others will certainly follow.

    The Telos VX emulates VoIP SIP phones, while adding important features that broadcasters need. These needs include phones with advanced screening features, high quality audio inputs and outputs with digital audio processing, a softphone with built-in recorder/editor, multiple program on hold inputs, and routing features that create the ability to move phone lines between studios effortlessly.

    Once you’ve identified what end points you wish to use, a switching platform should be chosen. You need to decide how much control and responsibility you wish to take on or whom you give it to. Delegating is good, but so is control. Traditionally, phone vendors performed installation and moves and changes. More than likely, you’ve taken on some IT duties over the past few years and are pretty familiar with the landscape. I’d say that the question to ask now is, “Do I want more control or less responsibility?”

    -- continued on page 3



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