Subject: Catastrophes and Line Load Control (A Forbidden Topic :-) )
Date: 20 Aug 89 22:03:25 EDT (Sun)
From: Larry Lippman <kitty!larry@uunet.uu.net>

In article <telecom-v09i0308m11@vector.dallas.tx.us> casey@well.sf.ca.us 
(Kathleen Creighton) writes:
> I saw "Surviving the Big One" produced by KCET (PBS) in Los Angeles and
> narrated by an LA fireman.  One of the statements he made was that in the
> event of a major earthquake which disrupts local phone service, we would
> still be able to call *out of state* via pay phones.

	Sounds like the fireman may be misinformed.  While coin telephones
would be given preference under conditions of Line Load Control (which
I will shortly discuss in more detail), anyone getting dial tone should
be able to call anywhere the cable plant and central office is intact.
This means that local calls would most assuredly be available.

	Cable plant restoral preference would no doubt be given to coin
telephones and subscribers deemed to be essential to the "public welfare"
(like police, fire, hospitals, etc.).

> (As an aside, he also said that the telco can only tolerate 10% of its
> pay phones being offhook at the same time so when you see a pay phone
> offhook after an earthquake, hang it up.)

	The above is no longer a particular problem with ESS CO's in
which software can simply ignore the scanning of a line in a permanent
signal condition.  In the case of SxS or crossbar CO's this was a
problem in that a linefinder-first selector was tied up in the case of
the former, and that junctors and permanent signal holding trunks would
be tied up in the case of the latter.
 
> [Moderator's Note: I am not sure why the *in-state/out-of-state* distinction
> was made. Did the commentator somehow feel that central offices handling
> long distance calls were somehow more immune to earthquakes or other problems

	It sounds to me like the commentator, who was obviously a fireman
and not a knowledgeable telephone company employee, was simply misinformed.

> And likewise, why did he think payphones were more reliable? A payphone
> inside a building which has collapsed is just as damaged as a private phone
> therein.

	Most BOC's have coin telephone vans available that are given priority
during restoral procedures following a catastrophe.  These telephone vans may
use wirelines for service, or may use IMTS or cellular radio for service.

> All telcos are able to provide simultaneous service to only about ten or
> fifteen percent of their customers at one time; and an even smaller number
> can be offered dial tone at one time. This is not a condition attributable
> just to coin phones. When all circuits/switching equipment/dial tone
> generators are busy, other customers sit with a 'dead' phone waiting.
> 
> Actually, the worst thing anyone can do in a time of national emergency
> is jump on the phone. Stay off if possible.

	The problem in a central office is that when it is overloaded with
call processing requests resulting from "real" callers or permanent signals
from damaged cable plant, NO ONE gets adequate service - not even essential
subscribers like police, fire, etc.

	To assure telephone service to essential subscribers, a special
procedure known as Line Load Control is often implemented in time of
local catastrophe or national emergency.  The existence and implementation
procedures for Line Load Control, believe it or not, is one of the most
closely guarded secrets of any telephone company.  In the case of BOC's,
Load Load Control procedures are covered in a "Plant Emergency Instruction"
binder with the pertinent section containing a large warning: "NOT TO BE
MENTIONED OR DISCUSSED WITH THE GENERAL PUBLIC".

	Line Load Control is implemented as a hardware function in SxS and
crossbar offices, and is implemented as a software function through the
maintenance tty in ESS offices.  Virtually all BOC CO's are equipped for
Line Load Control, except for perhaps small CDO's.

	In a CO equipped for Line Load Control subscriber lines are divided
into three classes: Class A, which comprises 20% of all CO lines, and which
provides service "essential to national defense and public welfare"; Class B,
which consists of 40% of the other CO lines; and Class C which contains the
remaining 40% of the CO lines.  In the case of a BOC, traffic engineering
personnel somewhat arbitrarily assign what lines go into Class A, with
Class B and Class C being randomly assigned to the remaining 80% of the
CO lines.

	When Line Load Control is enabled, only Class A CO lines are able
to obtain dial tone and originate calls, but such originated calls may be
completed to ANY line in the CO, including those in Class B and Class C.
When the Class A calling activity has stabilized, and if traffic capacity
permits, originating service will be ALTERNATED between Class B and Class C,
so that theoretically every working subscriber line has some chance to
originate a call.

	Implementation of Line Load Control requires an upper management
decision, and such implementation is not usually made unless a serious
local or national catastrophe has occurred.

	In a SxS or crossbar CO, Line Load Control is implemented by cutting
off battery to the subscriber line relays so that requests for dial tone
are ignored.  Such an action does not impair calls TO the affected lines.
In ESS offices Line Load Control is purely a software function such that
lines denied service are simply not scanned for off-hook condition.

	Perhaps the ultimate Telephone Status Symbol is having a Class A
line.  Why not call your local telephone business office and ask for one? :-)

<>  Larry Lippman @ Recognition Research Corp. - Uniquex Corp. - Viatran Corp.
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