[Asterisk-Users] Problem with ADIT 600 and FXO configuration

[Rich Adamson]

> > What does the TE406 leds indicate?
> 
> Both the ADIT 600 led and the TE406 led are green, the ADIT
> has zeros in the error counters.  Syslog has this as a final
> message after running ztcfg:
> 
> Nov 28 02:31:08 xxx kernel: Registered tone zone 0 (United States /
> North America)
> Nov 28 02:36:21 xxx kernel: wct4xxp: Clearing yellow alarm on span 1
> 
> I've seen documentation that says that telco-pots lines use
> loop start and I've seen mailing list entries that says you
> should use ground start for reliability.  Can anyone clarify
> this?

Back in the olden analog days, loop start trunks had an issue when
calls were simultanously started at each end of the trunk. There was
nothing built into the loopstart mechanism to resolve which end got
the trunk. As a result, two unknown callers would be tied together,
both complaining of wrong numbers.

Ground start trunks was a solution to that analog problem, thus making 
them more "reliable".

Other ways to make loopstart trunks more reliable included have one
end of the trunks always start using trunks from the low numbered end
(eg, 1, 2, 3), and the opposite end start with high numbered trunks
(eg, 24, 23, 22). The asterisk implementation of that is "g1" and "G1"
for zap channel order selection.

In lightly loaded systems the above is generally not a problem. On heavily
loaded systems with a reasonable mix of incoming and outgoing trunk
calls, loopstart trunks can be a slight problem that is most often
addressed through the trunk selection mechanism (eg, g1 vs G1).

Pure guess is the ground start functionality was implemented in asterisk
due to interface requirements to some legacy systems, and not as a
workaround for loopstart issues.

If your ADIT 600 has fxo cards in it, the selection of analog loop start
vs ground start will likely be dictated by whatever box or central office
switch your connecting the analog wires to. Loop start is by far more
common in todays telephony environment. Pots lines are always loop start
in the US.

Keep in mind that in the analog days, trunks were implemented with a 
series of relays (and other electromechanical devices), and there was
little that one could do in terms of controlling signal timing. That
timing could range from 100 milliseconds to as much as a second or so
depending upon exactly what equipment was used. With T1/E1's, signaling
happens in a few milliseconds and does not represent the same problem
magnitude.

Rich