[Asterisk-Users] far end disconnect supervision

[Rich Adamson]

> > > I'm starting to shop for my first channel bank and one of the features
> > > that eveyone seems to recommend is "far end disconnect supervision".
> > > What other terms do various manufactures use to describe this same
> > > feature ?
> > >
> > > Is "calling party disconnect" the same as "far end disconnect
> > > supervision" ?
> > 
> > Yes, in most readers terms. However, in some cases marketing/sales
> > people may have written stuff with no clue what they are talking
> > about.
> 
> 
> Is "far end disconnect supervision" BOTH a service/feature/line
> signaling provided by the Telco AND a feature of some channel banks ?
> 
> If some channel banks don't support this, how on earth do they know when
> the telco side of the call has hung up ?

If you go way back in history, channel banks were only used by telcos and
at least initially were only required to pass signaling between central 
office switches. It wasn't until fx cards were added that channel banks
had to be concerned with "calling" and "called" party disconnects. In some
states, the regulatory agencies governed what could (or could not) be
deployed and under what conditions. "Called party disconnect" was frequently
used by court order for police verification on certain calls, while
"calling party disconnect" was the norm. At that time, customer lines were
directly connected to the central office switch, and it was functions within
the switch that controlled calling/called party disconnects.

If the telco deployed a channel bank with fx-type customer interfaces, the 
channel bank would need to support "calling and called party disconnect" in 
order to inform the central office switch of call status.

If the telco deployed a channel bank with interfaces to a customer's pbx
where signaling used tones (as an example), the channel bank would not 
need the added electronics to support disconnect supervision.

Disconnect supervision refers to opening/closing the 2-wire circuit (as in
hanging up a telephone), and in some cases, reversing tip/ring (48 volt
polarity change).

(There are a number of other interfaces available for channel banks beside 
those designed for two-wire fx's.)

Since there are lots of old (and new) channel banks being sold on ebay, etc,
that may have been designed for different purposes, some will support
disconnect supervision while others do not, some are two-wire while others
are four-wire, some support E & M signaling (extra wires per channel), some
supply 100vac ringing voltage while others do not, some run on only 48 volt
DC power while others are 110 vac power, etc.

If you're looking for a channel bank to interface phones with asterisk, then
keywords would include "2-wire", "disconnect supervision", "fx lines", etc.
Might also ensure it can supply the needed 100 vac ringing voltage
(historically referred to as a ring generator).