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From: m21198@mwvm.mitre.org (John McHarry)
Newsgroups: comp.dcom.telecom
Subject: Re: Who's Using Whom?
Message-ID: <2910@accuvax.nwu.edu>
Date: 16 Jan 90 23:40:07 GMT
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X-Telecom-Digest: Volume 10, Issue 30, message 5 of 12


John Higdon wrote in V10 #29 that US Sprint was unaccessable during
the AT&T outage yesterday due to their leasing facilities from AT&T.

I don't know the specific access arrangements in his area, but I
believe the following to be generally true.  Carriers do lease trunks
to one another; however, these are non-switched services.  I don't
think AT&T has a tariff for switched access carriage for other IECs.
(Not too sure on that one) If that is the case, unless there was
indeed a cable cut, the common mode failure lies elsewhere.  Of
course, this leasing of trunks doesn't obviate US Sprint's claim
regarding an ALL fiber optic network if they lease only fiber optic
trunks.  There doesn't seem to be any claim that other networks don't
have some, or even lots, of fiber trunks.

What may be interesting here is the possibility of a shared BOC-AT&T
switch being in the common path, eg. the access tandem.  Unless I
misread an old copy of Notes on the BOC Intra LATA Networks, or things
have changed in the meantime, there are some switches that are either
BOC owned and used by AT&T or (the interesting case) AT&T owned and
used by the BOC.  These are an artifact of the pre-1984 state of
affairs, and represent cases where the split could not be neatly made
on one side or the other of the switch.  If Mr.  Higdon's LATA is such
a case, then US Sprint could be receiving service from the LEC, but
with an AT&T owned and operated switch in the middle.  In this case it
is the LEC that is providing service by leasing switch capacity from
AT&T.  US Sprint might well be using all their own trunks to the point
of presence.  Beyond that, they have no choice or control.

Of course, to the end user, this is cold comfort.  If there is only
one access tandem, you have no protection from a failure affecting it.
I suppose large users could use direct trunks to two or more IECs,
but, in most cases, that sounds like overkill, especially given the
probablility of the failure being guarded against vs the probablility
of backhoe fade knocking down both trunk groups.

These are only my own speculations, of course, and don't necessarily
reflect the views of anyone else.  If I have erred, I am sure I'll be
corrected.  On second thought, omit the if clause.
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* John McHarry    (703)883-6100             McHarry@MITRE.ORG *
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