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TUCoPS :: Phreaking Technical System Info :: acprefix.txt

Area Code Prefix Routing




From: goldstein@delni.enet.dec.com
Subject: Re: Calls With Area Code Prefixes
Organization: Digital Equipment Corporation, Littleton MA USA


In article <telecom-v09i0530m04@vector.dallas.tx.us>, dgc@math.ucla.edu
writes...

>Can anyone tell me exactly how calls with area code prefixes are
>handled?  Previous messages on the handling of 700 calls left me with
>some questions unanswered.  I think that there are basically 4 cases:

>1.  1-800 prefix

Two answers on 800 service.  Today, they use the "NXX" method.  Each
of the NXX codes (i.e., 800-221, 800-222, etc.) belongs to one or
another LD carrier.  The local telco simply hands it off.  Each RBOC
owns a few of its own, too, for intra-LATA use.  "Tomorrow" (R.S.N.),
there may be a huge telco-owned collective data base indicating which
carrier carries each 800 number.  So you will be able to switch
carriers without changing 800 numbers.  The problem is delay: There's
a finite time it takes the telco to send the lookup request through
the SS7 network to the data base engine (SCP).  It delays call
processing by a few seconds.  Other than that, the technique works
well.

>2.  1-900 prefix

Like 800 service today, each 900 prefix is handed off to an LD
carrier.  I don't think there are plans to change it.

Note that the caller's default carrier is not meaningful for these
SACs, since they're destination-selected.  The list of who owns which
was posted in this Digest a couple years back.  Note that these are
not area codes but service access codes.

>3.  1-700 prefix

This means "carrier specific number", so it's handed off to the
default or selected carrier.  Each carrier has its own 700 number
space to do with as they see fit.

>4.  All other prefixes

If it's intra-LATA, the telco just routes it.  If it's inter-LATA, it
goes to the default or (10xxx) selected carrier, who figures out what
to do with it.

>Why couldn't US Telecom just have you dial 11+local number if 1+ calls
>(other than 10+ calls) all go to it?  Is there some requirement that
>exactly 10 digits follow the initial 1? and couldn't that be handled by
>having the customer dial dummy 1's either at the beginning (say 1111) or
>at the end of the number (111) at the end?

The RBOCs are under no obligation to provide "equal access" for
intra-LATA calls; that's their own bailiwick.  If they did provide it,
they'd have to do it equally, like for inter-LATA calls.  The
numbering plan only has room for so many hacks.  It does involve digit
counting, etc.

     fred

------------------------------
From: David Lewis <nvuxr!deej@bellcore.bellcore.com>
Subject: Re: Calls With Area Code Prefixes (800 in particular)
Organization: Bellcore, Livingston, NJ


In article <telecom-v09i0533m06@chinacat.lonestar.org>, goldstein@delni.
enet.dec.com writes:

> In article <telecom-v09i0530m04@vector.dallas.tx.us>, dgc@math.ucla.edu
> writes...

> >Can anyone tell me exactly how calls with area code prefixes are
> >handled?  Previous messages on the handling of 700 calls left me with
> >some questions unanswered.  I think that there are basically 4 cases:

> >1.  1-800 prefix

> Two answers on 800 service.  Today, they use the "NXX" method.  Each
> of the NXX codes (i.e., 800-221, 800-222, etc.) belongs to one or
> another LD carrier.  The local telco simply hands it off.  Each RBOC
> owns a few of its own, too, for intra-LATA use.  "Tomorrow" (R.S.N.),

As soon as 80% of BOC end offices are connected to the Signaling
System 7 (common channel signaling) network.  At least, that's the
latest FCC ruling.

> there may be a huge telco-owned collective data base indicating which

Oh, please don't say "collective" in the same breath as "telco".  That
always makes people think of the other word that starts with "coll" --
"collusion".

A more accurate description of 800 Database Service (800 DBS) is that
there will me 800 databases owned by each telco, with the appropriate
information duplicated.

> carrier carries each 800 number.  So you will be able to switch
> carriers without changing 800 numbers.  The problem is delay: There's
> a finite time it takes the telco to send the lookup request through
> the SS7 network to the data base engine (SCP).  It delays call
> processing by a few seconds.  Other than that, the technique works
> well.

If your phone subtends an end office which is SS7-connected, the delay
is actually less than a second.  Delays only really pile up if the end
office can't send a query directly to the database, but has to hand
off the call to a tandem via MF (Multi-Frequency -- inband) signaling.
Then, it gets really bad.  That's one large reason why the FCC
mandated that the BOCs can't switch from the NXX method to 800 DBS
until 80% of end offices (actually, it may be 80% of end office lines,
but the economics fall the same way) are SS7-connected.


David G Lewis                                   ...!bellcore!nvuxr!deej
        (@ Bellcore Navesink Research & Engineering Center)
                        "If this is paradise, I wish I had a lawnmower."

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