“Voice Terminals”

Updated August 17th, 2015 at 9:00am to reflect changes and clarity and another update at 9:02am to fix grammar issues.

The definition in Harry Newton’s Telecom Dictionary   describes “voice terminal” as “a pretentious term by AT&T for a Telephone”. Sometimes that Aussie confuses me. One breath his book does not allow proprietary words but on the other page he’ll use an open standard definition but it’s still a proprietary protocol. Some other sites go so far to describe it as “pompous and confusing.”

Where I am going at is the phrase is actually not that far fetched. In most PBX systems (not limited to Avaya) most sets are basically just a device that talks to PBX, in which it resides. In actuality, the PBX is really where the call is placed and goes through and the same location where it receives calls. Comparing it to key systems, the PBX acts as the “brain” and the sets are similarly like dumb terminals. This is another reason why these sets cannot work on a landline, other than possibly short circuiting the network. In fact many digital sets use far less electricity than the analog counterparts, with many lines peaking at 100 volts.

In a terminal enviornment, when you push the Touch-Tone or DTMF buttons, what it does is it sends commands to the PBX to dial “5-5-5-1-2-1-2” then routes the calls to the appropriate trunk whether its local or long distance. Technically your call is actually being placed and located at the PBX and not at your desk. Modern PBX systems will also convert mediums to digital if say the trunk is digital. So I talk to a gal named Melanie on her Verizon iPhone from my Definity PBX, the conversation and the call I place goes to the switchroom. The Avaya DCP set at my desk is just extending it electronically so I do not have to be in a switchroom to talk.

Whatever vendor defines it (some call it a “telephone”, an “endpoint”, a “terminal” or what, the “voice terminal” is essentially the device facilitates  between the user and the PBX (the big iron or gateway sized.)

As defined in the glossary, traditionally the terminals would retrieve the line, and personal settings defined in the PBX at each port. In this example you’ll see a set properly set up as a particularly  extension and the other you will not.


This Avaya 6416 set is set up as a 6416 (or possibly a 6408.) The features that are designed to function as a 6400 series will work the way it should because this jack has it hard wired as an extension to serve as a 6408 series set.


This plugged into a jack that is set up to be an 8410 “Voice Terminal”, so this Avaya 6424 will literally take itself as an 8410. How? Because its built in clock doesn’t come on at all. If you press the date and time key it will, but for a few seconds. However the 6424 will refuse some softkey features like Inspect, because it has its own feature called Button View.

Early VOIP phones also ran as terminals, but as Session Initiation Protocol became standard, basically every SIP phone acted like its own PBX (and creating its own headaches.) Cisco’s Skinny Call Control Protocol or SCCP or Skinny, Nortels Unistim and Avaya’s DCP (allegedly) or a proprietary H323 protocol would mimic this terminal>PBX function.


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