[cisco-voip] FXO port to Viking C-1000B door entry controller

[Norton, Mike]

Hi Ryan,

I'm happy to continue discussing this topic but it might be a bit generous to call me a "master" at it. I welcome corrections from anyone if I say something incorrect. :-)


> As I understand supervisory disconnect (as it applies to this context), for the local-end to be hanging up, it would take the far-end generating a tone (or battery reversal/loss of battery) to "influence" the local-end to cause itself to hang-up its own equipment.... Is that a correct understanding of supervisory disconnect?

That's how it's supposed to work on analog POTS, yes. I'm not a big fan of the term, because I think of it as more "advisory" than "supervisory." I think of real disconnect supervision as a definitive two-way agreement that the call is torn down, e.g. via an out-of-band signal. But analog POTS does not have that.


> If the local-end generated too much far-end echo, couldn't that potentially cause the Viking to hang itself up (if the Viking is providing supervisory disconnect)?

By "hang itself up" I will assume you mean "want the call to end" rather than literally signal on-hook. Only the FXO side can signal hook status and actually tear down the call. To me, "hang up" normally refers to signaling hook status. The telco side does not have a handset to hang up nor a hookswitch to hang it on! ;-)

If there is lots of signal reflecting back off of the Viking, then that signal is not getting in to the Viking - it's bouncing off it. So no, I don't think that too much echo there would cause the Viking to notice anything or to alter its behaviour.

Even if the Viking did want the call to end for some reason, I would be very suprised if it provides any disconnect signaling. It appears to be a pretty simple box intended to be installed "in line" between a telco phone line and one or more POTS phones. The manual suggests that the way it "disconnects" after a door call is by connecting its phone output to its telco input. Signaling the phone(s) to hang up would run counter to the intended use case of putting PSTN callers on hold while answering the door.

-mn