[asterisk-users] GEN-GEN and Manual Ring-Down (MRD)?

Jorge Mendoza mendoza at tcc.com.pe
Tue Nov 11 11:07:55 CST 2008

Raj Jain wrote:
> On Mon, Nov 10, 2008 at 6:56 AM, Tony Mountifield
> <tony at softins.clara.co.uk> wrote:
>> Does anyone here know anything about GEN-GEN analogue circuits, also
>> known as Manual Ring-Down (MRD)? Apparently they are widely used in
>> Hoot'n'Holler systems for financial dealer-boards.
>> I have been asked to try and interface to such circuits, and have been
>> having great difficulty locating any specifications for the interface.
>> Apparently, they are always-on 2-wire analogue circuits with no tip
>> voltage or loop current, and on-demand superimposed ringing voltage in
>> either direction for signalling (to do nothing more than get the remote
>> end's attention).
>> I was wondering whether it is possible to adapt an FXS or FXO port to
>> operate in such a mode, but I'm not optimistic.
> Your understanding of MRD is correct (these are nailed-up connections
> with only ring-gen capability). I've personally not tried this w/
> Asterisk FXS/FXO ports but If you can make it work that way pls. let
> us know.
> --
> Raj Jain
The MRD telephones uses local battery, that is the reason why they do
not have loop current (central battery). Any adaptor to a FXS  circuit
is useless because there are not any signalling to indicate on/off hook.
Just the initial manual ringing.
Then working on FXS ports is almost impossible or very expensive.
Another approach is to use E/M signalling. The audio channel could be
open permanently and transmit the ringing over the E/M wires.  You need
a  ringing detector and a ringing generator in both sides. Take care of
isolate the audio channels from the ringing current. I do that many
years ago on PCM muxes with E/M interfaces.
The Multitech gateways have E/M interfaces, but never tested under this
Obviously, the easy way is to use two standard sets working as hotline.

Jorge Mendoza

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