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From: watson@im4u.UUCP (William J. Watson)
Newsgroups: comp.dcom.telecom
Subject: Submission for comp-dcom-telecom
Message-ID: <8705131734.AA25020@im4u.UTEXAS.EDU>
Date: Wed, 13-May-87 13:34:31 EDT
Article-I.D.: im4u.8705131734.AA25020
Posted: Wed May 13 13:34:31 1987
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Path: im4u!watson
From: watson@im4u.UUCP (William J. Watson)
Newsgroups: comp.dcom.telecom
Subject: Private PBX numbering, was Re: where has everyone gone and other stuff
Summary: Exists today on many PBXs
Keywords: PBX phone numbers
Message-ID: <1827@im4u.UUCP>
Date: 13 May 87 17:34:29 GMT
References: <8705121546.AA13873@ssc-vax>
Reply-To: watson@im4u.UUCP (William J. Watson)
Distribution: us
Organization: U. Texas CS Dept., Austin, Texas
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In many PBX systems, only some extensions have numbers directly accessible from
the public phone network.  Sometimes this is done to create "internal use only"
extensions, and sometimes due to the expense of buying a block of numbers from
the local phone company.  Usually, numbers are sold in blocks of 1000, but in
some congested ares (Downtown Houston, for example) they are sold in blocks
of 100.

In either case, some PBX systems have the option of a direct number for
"internal" access from outside.  In ROLM CBXs, this is called Direct Inward
System Access (DISA).  When you dial the DISA number from somewhere in the
outside world, you get a tone of some sort, at which point you can either simply
dial the number of the extension you want, or dial a special autorization code
that allows you to do anything you could from your office.  This can be useful
for making business long distance calls from home.

This setup would clearly only work for people with tone dial phones.  I think
that the possibility of rotary dial phones is ignored.

In any case, the numbers for all of the internal extensions are not used up
and, in some cases, a sophisticated network of internal extensions of internal
use only numbers can be set up, possibly spanning several sites.

William J. Watson
Member Technical Staff
ROLM, an IBM (cough, gag) company

All opinions expressed herein are my own.  My employer may not even know of them

-- 
William J. Watson
UUCP:  {gatech, harvard, ihnp4, pyramid, seismo}!ut-sally!im4u!watson
ARPA Internet & CSNET:  watson@im4u.UTEXAS.EDU