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<BODY bgColor=#ffffff>>The dial tone for the phone line still comes from the
CO. The phone companies >loop there copper cable in and out of the remote
cabinets. <BR>
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<DIV><FONT face=Arial size=2>Remote terminals are served by T1 or higher density
carrier circuits, which can be either copper or fiber, often employing
statistical multiplexing. While the DT may originate in the CO, it does so
only in a data sense, not an analog POTS sense. The remote terminal
actually generates the POTS analog signal, and is dependent on the life of the
batteries in the box. They are good for several hours, maybe even a day,
but definitely not weeks.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Some RTs also have a DSLAM associated with them for
DSL, but that is a separate topic and involves more batteries.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2><FONT face="Times New Roman" size=3>>This is
true, that is why most fire panels have to have 2 phone
lines.</FONT><BR></FONT></DIV>
<DIV><FONT face=Arial size=2>Which only catches about half of the problems,
assuming both come through the same cable from the same CO or RT (and, in the
latter case, the same carrier circuit). If a card fails or the I & R
guy opens or shorts the loop, the other line can take over. If the CO or
RT crashes, or batteries die or cable gets dug through by a backhoe, guess what
goes down! For serious mission critical circuits the engineer specifies
two different operating companies and requires each to provide complete circuit
details so he can insure that one isn't leasing lines from the other, or other
scenarios that would be vulnerable to a single incident.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV>>Time was a copper pair was supervised with a DC current from end to
end,</DIV>
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<DIV><FONT face=Arial size=2>Another variation on this theme used by central
alarm monitoring companies of years ago was to have the telco provide a copper
loop that included a number of customer sites. Basically each site was in
series. At the monitoring station was the DC power and a relay. If
all was well the loop was complete and the relay operated. Each site had a
mechanical interrupter--a spring wound gear mechanism that pulsed out digits by
breaking the loop momentarily. When an alarm condition occurred (such as
water movement in a sprinkler riser) the spring would wind down, turning the
gears and pulsing opens on the loop. In some cases, this caused ink mark
square waves that could be counted on paper. The pulses were similar to
rotary dial pulses in groups for digits, but slower speed. They
represented the ID number of the sender reporting, which identified the customer
and location.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Of course, if anything in the loop, any sender, any
telco drop, failed, the whole set of customers was unmonitored until it was
fixed--which could be a day or two in extreme cases. I was called out once
to service a site that had these. The one good thing about them was the
only electrical requirement was at the monitoring station.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Wilton</FONT></DIV>
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