Path: utzoo!attcan!uunet!tut.cis.ohio-state.edu!ucsd!ames!ncar!mephisto!ncsuvx!news
From: heath@shumv1.uucp (Heath Roberts)
Newsgroups: sci.electronics
Subject: Re: How to block incoming phone calls?
Message-ID: <1990Feb21.195852.23593@ncsuvx.ncsu.edu>
Date: 21 Feb 90 19:58:52 GMT
References: <8402@shlump.nac.dec.com> <1304@otc.otca.oz>
Reply-To: heath@shumv1.ncsu.edu (Heath Roberts)
Organization: NCSU Computing Center
Lines: 23

>> My understanding is that the ringing signal the called party gets and the
>> ringback (calling party hearing the ringing) are unsynchronized. Now, I 
>> _believe_ this might happen : your ring generator starts out in the quiet
>> portion of its ringing cycle, but the caller hears a full ring before your
>> circuit gets its ring, picks up the phone and puts a busy tone on it. 
>
>This is correct.  Unless the caller and person called are terminals on the 
>same exchange, the ring tone generated by the two exchanges (the exchange of
>the calling party and the exchange of the called party) are indeed 
>unsynchonised and hence the above scenario can happen.
>
Doesn't matter if you're on the same exchange or not. I've been working
on a switch , called a phone from another phone on the next _line card_
(they're about an inch apart) and they're not synchronized. There are
enough sync problems in a switch without worrying if you get ring and
ringback at the same time. It's not necessary and they're totally
different signals--why bother? 



Heath Roberts
NCSU Computer and Technologies Theme Program
heath@shumv1.ncsu.edu