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From: die@frog.UUCP (Dave Emery)
Newsgroups: sci.electronics,sci.astro,comp.dcom.modems,comp.misc,rec.ham-radio
Subject: Re: N.B.S. Time Service
Summary: Some calls are specially routed
Keywords: Time Ticks
Message-ID: <1120@X.UUCP>
Date: 8 Jun 88 09:00:00 GMT
References: <455@trane.UUCP> <4691@watcgl.waterloo.edu> <585@otto.COM> <317@ncar.ucar.edu> <587@otto.COM>
Reply-To: die@frog.UUCP (David I. Emery)
Organization: Charles River Data Systems, Framingham MA
Lines: 43

In article <587@otto.COM> glenn@otto.UUCP (Glenn Scott) writes:
>
>  Nevertheless, my point was that the receiver does not direct the routing.
>If I make a call, it is routed via the most viable route. Satellite delays
>notwithstanding.
>
>Glenn

	It is my understanding that the modern 4ESS/CCIS/SS7 AT&T long
distance switches (and probably other carriers as well) can and do
under at least some conditions selectively route calls to particular
destinations over particular types of media (such as fiber rather
than satellite).

	This capability was incorperated in the telephone network some years
back in an effort to reduce the number of sensitive conversations that 
are routed via certain microwave and satellite links that the Russians and
other foreign intelligence services routinely monitor.  As I understand it
the network is capable of refusing to route calls to particular specific
destinations via less secure paths if all the more secure ones are busy.
Further the detailed billing tapes available from your telephone carrier
contain information about how a specific call was routed and perhaps
whether it was specially routed or not.

	I do not know whether the software involved can specially 
process certain blocks of numbers within an office code differently than the 
rest of the office code but I suppose this is quite possible.
	
	Whether the knowlage of what numbers to process specially is
contained in a database at the originating toll center or whether the
destination serving toll office can pass back a CCIS message identifying
a number as requiring special handling I do not know.

	It is therefore quite reasonable to suppose that when the NBS time
number is called it is specially recognized and the call routed via
terrestrial rather than celestial paths at least over AT&T.       -- 
----
David I. Emery
Charles River Data Systems
983 Concord St.
Framingham, MA 01701
Tel: (617) 626-1102
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