[Asterisk-Users] adtran 750 + t100p

[Rich Adamson]

> Thanks, from what I've gathered, remote disconnect supervision (hangup
> detection) requires kewl start signaling.  I currently have loop start
> signaling ...will the telco change the signaling on the line ?
> 
> Or will the L36 firmware in the adtran make this work fine with loop start
> lines ?
> 
> There seems to be conflicting opinions on this.
> 
> I'm assuming FXO cards in the adtran 750 pushing incoming calls to a t100p
> will take care of my echo issues.

There seems to be a fair amount of misunderstanding, etc, about the disconnect
supervision issue. Let's see if we can put some facts around at least some
of it. 

Calling vs Called party supervision: some telcos have central office equipment
that supports both, however some (at least in the US) are "calling" party
supervision only. If asterisk is the calling party (via the pstn to some
called party), the Called party can hang up without any notification 
being sent back to the Calling party. (Eg, telco equipment dependent, but
generally configurable if you can find someone that knows the equipment.)

Some telco equipment will signal when the remote phone/system has hung up.
On loop start lines (including kewl), that signal is typically a change in
tip/ring loop currect, going from roughly 20-30 milliamps to zero for some
short period of time (less then a second). If the telco equipment supports 
that, you can see it by simply attaching a cheap voltmeter across the tip/ring 
pair and watching when the remote party hangs up their phone. You don't need
asterisk or anything else but a phone and voltmeter to test it.

E&M trunks were invented a million years ago as one mechanism to get around
the less reliable loop signaling. E&M trunks are typically four or six wires.
The four wire consists of a single tip/ring full-duplex transmission pair,
plus an E-lead (supervision in one direction) and an M-lead (supervision
in the opposite direction). Six wire E&M trunks have the transmit and receive
transmission paths separated into a two-wire transmit plus another two-wire
receive pair (not much of a need for echo suppression in it). E&M trunks are 
not very popular in the small pbx environment primarily because the telco 
has to provide another layer of equipment (typically a T1 mux plus a T1 line) 
at your location in order to derive the four or six wires needed within the
limited-distance interface specs.

Channel banks (including the Adtran products) can be engineered to support
each of the above with different cards, or none of the above (no remote
disconnect supervision). There have been a significant number of list postings
over the last six months relative to which channel banks to avoid for this
very reason. I don't have an Adtran 750, so I'd have to go dig through their
spec's to see what they do support. Since it seems to be a rather popular
mux, I'd have to guess that it does support remote disconnect supervision.
Sensing the drop in loop current would require at least some electronic
components for detection on the card, therefore its _not_ just software. 
The specs for the mux cards should tell you.

You will find a fair number of carrier class (older) channel banks offered
on eBay, etc, that do not support remote supervision. They were primarily
engineered to pass multi-frequency tones through the transmission channel
for supervision and control as opposed to using loop start or E&M signaling.
Those are the ones to avoid.

Rich