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From: kitty!larry@uunet.uu.net (Larry Lippman)
Newsgroups: comp.dcom.telecom
Subject: Re: What Kind of Switch is This?
Message-ID: <11926@accuvax.nwu.edu>
Date: 9 Sep 90 16:23:17 GMT
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In article <11794@accuvax.nwu.edu> dave%westmark@uunet.uu.net (Dave
Levenson) writes:

> A customer has a loop-start CO line (it happens to be the first in a
> small hunt-group) where outgoing service is normal.  On incoming
> calls, the caller hears the ringback tone, but no ringing voltage at
> all is delivered to the line.  Listening with a butt set (in monitor
> mode) when an incoming call is attempted, one hears absolutely nothing
>  ... no clicks, no tones, and no ring power.  But switch to talk mode,
> and you answer the incoming call and can converse with the caller.
> The CO is probably a digital time-division switch of some kind, as
> there are no audible clicks or loop current interruptions when calling

> Has anybody ever heard of this failure mode?

	Assuming that it is a digital CO, the ringing control is
provided directly by the subscriber loop interface circuit.  Since
ring control circuitry is unique to each line, a failure mode can
exist which affects only a single line.  Failure of the ring control
switching element (could be either solid-state or a relay, depending
upon the type of CO apparatus) that switches the ring conductor
battery feed between -48 volts and -48 volts superimposed upon 20 Hz
ringing could cause the *exact* problem you are describing.

> I wonder if the CO is administered
> with none of the possible ringing options selected?  (No, it's not tip
> party, it's not ring party, it's not bridged ringing, etc.  None of
> the above?  Don't ring at all!)

	My intuition is that it is a simple hardware failure as
described above, and not an administration error.  Besides, in most if
not all digital CO apparatus, party line control requires a subscriber
line interface card which is *different* from than that used for
regular single-party service.  Since it is not likely that such a card
would be furnishing service to the above single-party subscriber, such
an administration error is most likely physically precluded.


Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
     {boulder||decvax||rutgers||watmath}!acsu.buffalo.edu!kitty!larry
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