Date: Mon, 7 Sep 92 12:10:15 CDT
From: varney@ihlpf.att.com (Alan L Varney)
Newsgroups: comp.dcom.telecom
Subject: Re: Bad Connection to MCI
Organization: AT&T Network Systems, Lisle, IL
X-Submissions-To: telecom@eecs.nwu.edu
X-Administrivia-To: telecom-request@eecs.nwu.edu
X-Telecom-Digest: Volume 12, Issue 692, Message 1 of 8

In article <telecom12.680.3@eecs.nwu.edu> sullivan@riemann.geom.
umn.edu (John M. Sullivan) writes:

> A friend of mine just moved to a new apartment yesterday, here in
> Minneapolis.  Her phone was connected by US West on schedule.  She
> requested MCI Dial-1 service ...

{Summary: 1 + ten-digit dialing lead to regular Vacant Code
announcement with "2EB" appended.  So did 1+ 700-555-4141.  10222 + 00
worked, but 10222 + 1 + ten-digit didn't.  10XXX to AT&T/Sprint with
ten digits worked.}

   I have an explanation at the end, but you'll need the material
below to understand it.

> This, and the "2EB" code in the message, led me to believe that the
> problem was MCI's.  ....  {Placed 3-way call between MCI and USWest.}
> ....  They were both agreeing that my problems were due to
> USWest not having put in the Dial-1 choice properly, and I couldn't
> convince them otherwise.

    I'll side with MCI here (and that's not frequent) -- Vacant Code
is USUALLY from three possible points on an inter-LATA call:

  - the originating CO when it finds a routing error on the call,
    and the error isn't due to 10XXX, 1+, 0+, or international 
    prefix digits; (Classic case is the NPA-NXX does not exist.)

  - the first switch reached in the terminating LATA determines that
    it's not the proper IC delivery point for that NPA-NXX; or

  - an IC switch believes the NPA-NXX doesn't exist -- in other
    words, there is no LATA that owns the NPA-NXX.

   Some ICs alter the wording somewhat from the Bellcore suggested
Vacant Code announcement, allowing this case to be distinguished from
the LEC cases.  The second one (terminating LATA) can be detected
(until SS7) by the time delay in getting to the LATA.  90% of the
time, it's a customer dialing error and/or CO routing error detected
at the originating CO.

> At one point the conversation went:

> USW: Is your pick code two-twenty-two?
> me:  Yes.
> USW: Is she [MCI] still on the line?
> me:  I don't know.
> MCI: Oh.  What?
> USW: Is your pick code two-twenty-two?
> MCI: What's a pick code?
> me:  You know, like one-oh-two-two-two.
> MCI: Oh, I've never heard it called a pick code. [Neither had I]

> Does anyone out there know what's going on here?

   Correct non-lingo version of conversation:

USW: (to the IC) Is your Carrier Identification Code two-two-two?
MCI: Yes it is.

   Carrier Identification Code (CIC): The XXX (or XXXX, soon) digits
that select a particular Carrier.  CIC can also mean Circuit
Identification Code (labels a particular trunk in SS7); those
documents that refer to both have started using TCIC for the latter.

   Carrier Access Code: The code dialed by a customer to select a
particular Carrier (10XXX or 950-WXXX today).

   PIC (pronounced "pick"): Pre-subscribed InterLATA Carrier -- the
value of the CIC you have selected (if any) to carry Inter-LATA calls
dialed without a Carrier Access Code.

   ICs are not familiar with the term PIC because it is typically used
only by people who deal with IC pre-subscription in the CO.

> What message should I hear when dialing 1-700-555-4141 if no carrier
> is selected for Dial-1?

   The announcement for "10XXX Omitted when Required" is:

   "We're sorry, a long-distance company access code is required for
the number you have dialed.  Please dial your call with the access
code."

   But an (option) allows regular Vacant Code to be used, and many COs
pick that option.

> (If I dial 10-xxx-1-700-555-4141 for a random choice of "xxx", I hear
> a very long pause with some touchtones in the background, and finally
> "doo-wee-dee Your call failed.  Please try again".)

   This is not consistent with your claim that 10288 and 10333 would
complete ten-digit calls.  Nor is the announcement consistent with the
selection of an invalid XXX value.  Maybe you picked XXX values for
ICs that don't support "700-555-1212" identification.

                            ------

   So here's my analysis (with the help of a couple of Interconnect
experts):

   10XXX + ten digits works for other carriers, so your line has not
   been denied all InterLATA calls.

   10222 + 00 works, so you are not totally denied FG-D access.

   You implied 10222 +0 + ten digits didn't work.
   Answer -- there is a "feature" called Selective Carrier Denial
   (SCD) that prevents all access to an IC (or list of ICs) except
   for 10XXX + 00 and 1 + 800 calls.  (Actually, I believe 00 also
   works if your PIC is one of the denied Carriers).

   I'd give this a 75% chance of being the root cause.  How much more
do you want for free?


Al Varney -- remember, just MY opinion.