[asterisk-dev] wctdm 4/8/24 VMWI generation capabilities

[Alec Davis]

I've been looking over the code for the wctdm and the wctdm24xxp looking for
clues on how to turn on the message waiting lights of various connected
analog phones.

I see there has been some work regarding neonmwi monitoring for an FXO port,
but couldn't find anything to generate the VMWI for an FXS port.

There are various forms of VMWI that seem to be around;
	FSK sending to an On-Hook phone, Here in NZ Telecom do that when you are
subscribed for message waiting service, hence many phones available here
support it. There is no 'wake up' event though, like a ring burst, no line
reversal, no zero voltage, just the FSK data.
	Other phones available have line reversal, MWI. This works by reversing the
idle line voltage while messages are waiting, the same phone DORO AFTI 22
also supports Neon High voltage MWI.
	Neon High voltage (90V) set on the line while messages exist, either
permanantly or flashing.
	Stutter Dialtone, only informs the user they have messages when going
off-hook, is a very manual process to be alerted if messages exist.

The wctdm code has 'reversepolarity' variable throughout the code whereas
the wctdm24xxp which I guess started from the wctdm base code hasn't.
What was the intention of the 'reversepolarity', as it feels like the right
variable to manipulate if there are messages waiting for this extension?

The bigger project is to support MWI FSK data periodically sent to each FXS
port.

Alec Davis