Date: Wed, 29 Jul 92 03:43:17 CDT
From: varney@ihlpf.att.com (Alan L Varney)
Newsgroups: comp.dcom.telecom
Subject: Re: Is Not 100% SS7 Needed For 1-800 and the Like?
Organization: AT&T Network Systems, Lisle, IL
X-Submissions-To: telecom@eecs.nwu.edu
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X-Telecom-Digest: Volume 12, Issue 593, Message 3 of 8

In article <telecom12.589.2@eecs.nwu.edu> shri@iucaa.ernet.in (H.
Shrikumar) writes:

> Please correct me, if I am wrong ... no scratch that, reading the
> above, it *does* seem that I *am* wrong ...

> I was under the impression that 1-800 like services could not be
> implemented really well without the something like SS7.

   Jee, I don't know; I thought 1-800 worked "really well" before SS7
existed ... :) In the beginning, 800 was implemented by setting up
lots of switch translators -- the final destination was usually a
number like NPA-015-2345, for Band 5 calls.  Then CCIS 6 made possible
the 800 database, and AT&T started using it to both screen for Band
violations and to derive the destination number.  This worked well
until divestiture, when everyone (LEC and IXC) wanted 800 numbers and
their own databases.  The current scheme pre-allots 800 NXXs to
carriers, and sends the calls to them with FG-D signaling (ANI, etc.).
Each carrier has their own database(s) and scheme for accessing
it/them.

   As a long-term objective of divestiture, the "industry" was to
develop a means for assigning 800 numbers to carriers on a 10-digit
basis, and provide a means to change that association.  Bellcore's
scheme for this is described in TR-TSY-000024, called "800 Number
Services".  In general, this uses SS7 from an End Office (EO) to query
a database that will return an associated carrier and (possibly) a
destination number.  Where the EO does not have the feature, either
FG-D MF or SS7 or ... can be used to reach a Tandem switch that can
then query the database.  If a non-LEC carrier is associated with the
number, the carrier can be reached using FG-D or SS7 signaling.

   Much of the push for SS7 interconnection now is to reduce the
"post-dial delay" associated with the FG-D signaling scheme combined
with the use of a Tandem to do the query.  For example, today's 800
call could go direct to an IXC from an end office, using about 22 MF
digits.  With TR-24 and a Tandem, there's 28 digits to the Tandem (in
two stages), a query/response delay, then 22 digits to the IXC.
That's roughly 3.5 seconds added delay in delivery.  SS7 can cut that
delay by querying directly from the EO, or using SS7 to the Tandem, or
using SS7 to the IXC from either the EO or the Tandem.  The current
version of the FCC 86-10 ruling is designed to reduce the delay in two
stages, while speeding up the availability of "portable" 800 numbers.

> ... Are we reading in the above that there is not yet 100% SS7
> interconnects in the US?

   Yes and no.  Calls in general will not use SS7 between the LEC and
IXC TODAY.  But most are interconnected with SS7 in some fashion in
order to verify Calling Card numbers, line restrictions, etc.  This
was needed in order to comply with an earlier timetable for removing
LEC access to AT&T's old line databases (CCIS 6 access).

> IS it that 1-800, ANI and caller-ID are being done by some other
> means (I'd have to do some learning here then.) or is it that the LD
> carrier do use SS7, and only that some local links are not yet ?

   Caller-ID today is primarily restricted to intra-LATA SS7
connections (but CCIS 6 was used for some early trials).  The current
NXX-based 800 access scheme and ANI are available with MF signaling,
but are also supported with SS7.  Where did you get your information??


Al Varney - just MY opinion.
This information IS available from the FCC and other sources.