Date: Wed, 29 Jul 1992 13:20:21 GMT
From: deej@cbnewsf.cb.att.com (david.g.lewis)
Newsgroups: comp.dcom.telecom
Subject: Re: Is Not 100% SS7 Needed For 1-800 and the Like?
Organization: AT&T
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 12, Issue 593, Message 4 of 8

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

> In article <telecom12.576.1@eecs.nwu.edu>, john@zygot.ati.com (John
> Higdon) writes:

>>> Regarding SS7 links, he said GTE was working on them between their own
>>> switches.  Links to PacBell would come, but he didn't know when.

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

"Really well" being a loaded phrase, I'm going to avoid using it ...
800 services can be and are implemented without SS7 network
interconnect between LECs and IXCs (and between BOCs and other LECs);
in fact, 1992 being the 25th anniversary of 800 service, it is obvious
that 800 service worked fine before the world even heard of SS7.

What I suspect you're thinking of is twofold:

1. Current 800 service implements carrier selection by the "NXX"
method, a.k.a. six digit translation in the originating LEC network.
Each 800 NXX prefix is assigned to a single 800 service provider.  The
originating LEC end office or access tandem performs a six digit
translation on the dialed 800-NXX number and uses that to route to the
appropriate carrier (IXC if an IXC NXX, performs a database dip if the
LEC's own NXX, reorder or announcement if some other LEC's NXX).

FCC docket something-or-other orders what's commonly known as "800
number portability", wherein the 800 numbering space will be
partitioned amond service providers on a seven digit basis instead of
a three digit basis.  This requires that the originating LEC network
route on ten digits instead of six.  Because this amount of
information can't be stored in a switch, the originating LEC switch
will (in most cases) route the 800 call to its access tandem, which
will query a database (800 Service Control Point) to determine the
carrier to which to route the 800 call.

2. Because an additional database query is being used in the
originating LEC network, call setup delay will increase by a
non-trivial amount.  The FCC, in the same docket, therefore imposed
fairly strict performance requirements (which are, I believe, a median
time for calls to be delivered to the terminating LEC of less than 2.5
seconds by sometime in 1993, and a 95%ile time for calls to be
delivered to the terminating LEC of less than five seconds by sometime in
1995).

To meet these performance requirements calls for a fairly high level
of SS7 implementation, both in the LEC networks and LEC/IXC network
interconnections.  (The IXCs internally are almost, if not completely,
100% SS7.)  Therefore, to implement "800 number portability" requires
high (although not 100%) SS7 implementation.

> 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 ?

Both.  800 calls are sent from originating LEC to IXC to terminating
LEC via whatever signaling method happens to be in place.  Wherever
the 800 database query occurs, some kind of out-of-band signaling has
to be available (SS7 in almost all cases today; historically, AT&T
used CCIS - SS6 - for queries before SS7 was around).  ANI delivers
the Billing Number from the originating LEC to the IXC via equal acces
MF signaling; this can then be carried through the IXC network if the
network supports it, such as in the SS7 Charge Number parameter.  It
can then be delivered to customers which are directly connected to the
IXC network (via T1 carrying either ISDN Q.931 signaling, or MF/DTMF
which has been modified to deliver the billing number in a way similar
to equal access MF).  There is currently, short of SS7 network
interconnect, no way to deliver calling party number or billing number
from the IXC to the terminating LEC.

Hope that answered your questions.


David G Lewis                              AT&T Bell Laboratories
david.g.lewis@att.com or !att!houxa!deej     Switching & ISDN Implementation