[Asterisk-Dev] Raising loop current limit on the Proslic (reg.71)

[Rich Adamson]

> > After I hit send I realized I was "out of context" with the original
> > topic. For the central office based loops, the 12 to 30+ still holds
> > true for many CO switches. There are still a large number of CO switches
> > that are not current regulated loops; those are still I=E/R with E fixed
> > at -48 and R varing depending on the distance. Try some 10 mile loops. ;)
> 
> Yikes.  I was not aware of this.  Thanks for the note though, along with 
> Matteo's fixes for "heavier" loads for the TDM400P I think the archives are 
> much better off for it all.  :-)

Not that this has any real value, for grins I just checked one of our pstn
lines. Stats: 51.8 vdc and 31 ma actual using a very old ITT desk phone.
The short-circuit current (placing a ammeter directly across the tip/ring 
pair) was 37 ma, indicating the copper plant plus CO hardware was the 
equivalent of 1400 ohms.  I don't have a clue what gauge of copper plant 
the telco is using, but I do know we're on an electronic CO and within 
dsl distance. (26 gauge telco cable runs about 80 ohms per 1,000 feet.)

So from that, its fairly easy to determine whether the central office has 
any form of current-regulated loop, and obviously in this case it does not
(31 ma verses 37 ma). Pure educated guess is we're about 10,000 feet from
the central office. I've not heard of any case where a central office 
provides current-regulated loops, but then I'm not in a position where I 
would have any need to hear about them any more. (They may exist, just 
don't have a real clue.)

For someone that is located right next door to the central office, I'd
expect to see about 70 ma while someone five miles from the office is
likely to see about 15 ma (give or take a little depending upon how the
copper was engineered, etc). There is no such thing as a 20 ma standard
or telco objective in the US other then as a order of magnitude value.

As a side note, I also checked the "remote-disconnect-supervision". It
consisted of approximately a one-second open loop (no current whatsoever)
about five-to-seven seconds after the remote party hung up. (I'd suspect
this is also central office equipment dependent and probably varies some
between different types of offices.)

Isn't trivia fun. ;)