textfiles/phreak/SWITCHES/class.txt

                   Custom Local Area Signalling Services

                        Written by: The Videosmith

                              Version - 1.1

----------------------------(c) Copyright 1994---------------------------

This article will explain the newly developed LASS system (AT&T Bell Labs),
and how it may affect us in the near future. Note that the service as it
appears for customers is called "CLASS", the C standing for Custom. I
assume this is just for looks.

LASS
----

   The telephone was destined to become a well used and powerful tool for
otherwise tedious tasks. Gas meters and other metered services would be
surveyed through the use of automatic data retrieval employing telephone
communications. All in all, some have big plans for the uses one could put
the telephone system up to, and CLASS is one plan that is going to drop an
innovative bombshell on the telecommunicating world.

   At this moment, a local CCIS network feature is being developed by Bell
Laboratories. This feature will change the way people use fones, and will
also change the attitude in which they use them. It will give far more
control of the telephone to the user than ever before. This feature is
called CLASS (Custom Local Area Signalling Services).

   Everyone will find something useful in this newly developed telephone
feature. Pizza parlours will no longer have to worry about fraudulent
italian food mongers, and little old ladies won't have to worry about prank
calls by certain dubious characters.

   What are all these fantastic features?  These features will include call
back of the last caller, regardless of whether you have their telephone
number or not. Another will be distinct call waiting tones, and preselected
call forwarding (only those people whom you wish to speak to will be
forwarded). This is a rudimentary list of CLASS features to come.  It is a
very powerful system, and it all relys on LCCIS (Local Common Channel
Interoffice Signalling), an intra-LATA version of the ever-popular CCIS.

CCIS Background ---------------

   CCIS was originally introduced in 1976 as, basically, the signalling
system to end all signalling systems. Instead of using the voice grade
trunks to carry signalling information on, a data network would be used.
This network is comprised of data links from each TO [involved with CCIS]
to the appropriate STP (signal transfer point). Signalling information is
sent through these links at 4800 bps to the STPs (Note that baud rates may
increase due to the economic availability of faster data communications
hardware), where stored program control routes the signalling information
to the needed offices in order to open and complete the call path. SPC
checks automatically for on-hook/off-hook status before opening the path,
and if the status is off-hook (in this case the customer does not have the
call waiting custom calling feature), returns information to the
originating CO to apply a busy signal to the customer. This is but one of
many features toll CCIS provides the network with.

   Since this text is not centered on the topic of toll CCIS, technical
aspects aren't as important (except for the comparison between the local
and toll networks for observational purposes): yet it is important to
notice how automated and flexible this type of signalling method is, as
well as its speed and efficiency. All the software control involved with
local and toll networks is called, fittingly, the "stored program control
network." or ISDN (Integrated Services Digital Network). LCCIS will be
addressed in a future article.

CLASS/LCCIS Features --------------------

LCCIS would look like this:



                                  /--\
                                  CO-2
                                  ESS#
                    /----I-T-G-----1A-----I-T-G----\
                    |             \--/             |
                    |               |              |
                    |             LCCIS            |
                    |               |              |
                    |          ----------          |
                  /--\--LCCIS--|CCIS/SPC|--LCCIS--/--\
                  CO-1         ----------         CO-3
                  ESS#                            ESS#
                  -1A----interoffice trunk group---1A-
                  \--/                            \--/

SPC = Stored Program Control (Network control and Signal Transfer Point)
ITG = Interoffice Trunk Group

   Using a high-speed data link between local offices creates a much more
flexible and more effecient way for intra-LATA central offices to communi-
cate. Instead of using per-trunk signalling (using the same trunk used for
voice transmission to send routing and billing information), such data
would be sent thru a 2400 bps dedicated data link, which interacts with a
local signal processing and transfer point. From that point, signalling
information is distributed to appropriate central offices or tandem
switches.

At the time during which this article was being initially researched, CLASS
was only being developed for the #1A ESS switch due to the flexibility of
it's memory handling, it's speed and what Bell Labs called 'cost
efficiency'. At the end of the research involved with this article, CLASS
was already implemented in data stage on ESS#5.

   LCCIS will work with the local switches using stored program con-trol,
keeping track of call data. The 1A switches will use what is called
"scratch pad" memory (also known as call store), in conjuction with LCCIS's
database, to accomplish all the features that LASS provides.  This memory
will hold such data as "line history", and a "screening list".  That
information will make it possible for autoredial, selective call
forwarding, nuisance call rejection, and distinctive call waiting tones.

Selective CF ------------

   Selective call forwarding is defined by the subscriber (the sub-scriber
must have conventional call forwarding to request this service).  Using
call store, or more specifically the screening list, one will be able to
selectively forward a call to another directory number by executing a few
simple commands on the friendly home-bound telephone (unlike migrating
telephones most frequently found in hotel rooms). An access code (a list
will appear at the end of the file) will be entered, and a special tone
will be issued from the subscriber's CO. The cus-tomer will then dial in
the numbers he wants forwarded to the particular number. After each number,
a tone will sound indicating the acceptance of the number. Individual BOC's
(Bell Operating Companies) will be able to define the amount of numbers
which may be screened. Once this is done, the cusomter hangs up and the ESS
takes over. Now, whenever some one calls this particular customer, the
customer's switch will compare the calling line's directory number with
those stored in scratch pad memory. If the CLID matches one of the numbers
in 1A memory associated with the called directory number, the number is
forwarded. If not, the phone will ring at the original destination. This in
particular could make it very difficult on system hackers, as you could
probably imagine. A company can subscribe to this CLASS feature, and enter
only the numbers of authorized users to be forwarded to a computer. Bureaus
inside the various telephone companies and other sensitive operations can
screen calls to particular numbers by using this service.

   This is a security that's hard to beat, but of course there is a way
(simple law of nature: nothing is fail-safe). There will always be the
obvious way of finding numbers which are being forwarded to, like auto-
dialing entire exchanges (one after the other). Unfortunetly, CLASS will be
providing other services which might make "scanning" seem less attractive.

Distinctive Ringing
-------------------

   Distinctive ringing is handled in the same fashion as selective call
forwarding is: the screen list in scratch pad memory. The customer may
enter numbers which the ESS should give special precedence to, and when-
ever a call is placed to this particular customer's number, ESS checks to
see whether the CLID matches a directory number listed in the switch's
memory. If a match is made, the subscriber's CO gives the off-hook line a
special call waiting tone, or the on-hook phone a distinctive ring
(possibly using abnormally timed ringing voltage... some readers may
picture a British Telecom ring as an example, although many foreign audible
rings tend to be different).

Call Rejection
--------------

   Nuisance call rejection, a feature making it possible to block certain
idiots from ringing your fone (a feature we can all benefit from at one
time or another... or all the time), uses the information retrieved from
LCCIS (CLID).  Let's say customer A calls customer B:

                              ----LCCIS----
                    A ---> CO<             >CO ---> B
                              ----trunk----

   Customer B happens to despise customer A, and keys in a special *##
code. ESS again takes over and looks at the CLID information, and stores
the calling line directory number in a special screen list associated with
with customer B. The next time customer A tries calling customer B, the
terminating office will reroute the call to a local (the originating CO)
digitized recording telling customer A that the call he made cannot be
completed due to customer B's request ("I'm sorry, but the customer you
have tried to reach wishes you were eaten by a rabid canibal on drugs").

Dial Back
---------

   To create such a feature as "dial back" (for called or calling party),
the ESS scratch pad memory is used again. The same principles are used as
are employed in the already established custom calling feature, auto-
redial. CLID will be used in this way:

                                    (received from CLID)
                  last-called-mem     last-caller-mem
                     ----------          ----------
                     |###-####|          |###-####|
                     ----------          ----------

   Your ESS switch will keep track of who you called last, and who called
you last, thru the retrieval of calling line information provided by LCCIS
in conjunction with your switch (Your switch will know what number you
called last by directly storing the digits you dialed previously. Local
signalling will provide calling line information via LCCIS call information
forwarding using the data link mentioned). This way, with your access code
(*##), you will have total re-dial service.

Customer Trace
--------------

   This type of memory handling and signalling method will also allow the
feature that everyone was afraid would abolish "phreaking". Subscriber
initiated tracing, using the last caller directory number stored at your
CO, will be available as far as Bell Laboratories is concerned. There seems
to be two types of "customer originated trace". One will forward the number
to local authorities, at  which it will be handled through the police. The
other feature AT&T/Bell Labs is working on will be a display module that
will sit by your fone, and will display calling directory numbers. All
other CLASS features that use the calling line information are used at the
descretion of the caller. The customer originated trace, however, using the
individual or bulk calling line identification features ("trace") allow the
customer to view the calling number. The world is not ending... yet, in any
case. Individual customers will be able to employ a special "privacy code",
which when dialed, tells the far-end switch not to forward the calling
number to a desk display.  Whether there will be a way to override this or
not is obvious: of course.  The police, the military and government
agencies are all likely to have a higher priority level than your privacy.
It seems that long distance carriers could benefit greatly from CLASS. Why
Bell/AT&T should give any type of special services to OCCs not given to
other non-telephone companies, especially after equal access is fully
implemented, I don't know (but then again, it is EQUAL access). It's always
possible. It is also possible that there will be no desk display. There are
those phone phreaks who feel that BOC's will never give the end party the
priviledge of retrieving the calling party's number directly, if not due to
plain old Bell policy on the issue of privacy. We'll have to wait and see
about that point: the desk display is, in fact, operational and is being
used in test stage. Whether Bell Labs feels that this feature can and will
be used in a full scale non-beta stage BOC situation is a different story.
The economic feasability is questionable.

End Notes
---------

   CLASS, using local CCIS, will not function on inter-LATA calls. The
local CCIS network is exactly that: local, and does not extend into the
realm of "toll network". This will eventually be corrected (allowing toll
CCIS to interact with LCCIS as far as CLID information is concerned). How
the various long distance networks will exchange information with the local
BOC network has not been determined [by the writer of this article]. It
would seem like a monumental task to try to integrate the emerging long
distance companies into the AT&T/BOC ISDN, be it because of equipment
inconsistancies or lack of cooperation on the part of the OCC, etc. This
will be discussed in an upcoming article dealing with toll CCIS.  Although
CLASS has been built around the ESS #1A switch, it has, as has been
mentioned, been co-developed for use with the ESS #5 switching machine.

   CLASS is going to cause problems, as well as create a new environment
for telephone users. Of course, those problems are only problems to people
who will generally be reading this article, but the more you know about
CLASS the more comfortable you'll feel about the service. It can be used to
one's advantage, even as a telecommunications hobbyist. Just as a
corporation will be able to set up a complete history of who is calling
their system, and eventually keep people off the system using the screen
list in memory, the same features can be applied to bulletin board systems
and the like. Imagine being able to keep all the local bozos off your
board, or being able to screen all but your private local users (making
your system completely inaccessible through the PSTN network from any
telephone but that of one of your users). It would seem to be a useful
feature, if nothing else but an easy feature, to implement.

   It is a little difficult, if not plain awkward, to write an article
about a topic which is subject to change at the researcher's ignorance. I
think that CLASS is enough of a momentous issue that at least some text by
a hobbyist should be released for public knowledge purposes.  Yet my
awareness of the fact that some of this text may be outdated, or
inaccurate, by the time CLASS is released as a BOC service, is in itself
the explanation of why there is a version number at the head of this
article. Most likely, when CLASS becomes public, the second version will be
released with update notes (if need be...most probably so). I hope you
enjoyed it,

                                               The Videosmith.  LOD/LOH!

---------------------------------------
Test stage defaults for some features:

DTMF ! Pulse ! Description of Service
---------------------------------------
 *66 !  1166 ! Reconnect last caller
---------------------------------------
 *63 !  1163 ! Selective Call Forward
---------------------------------------
 *60 !  1160 ! Nuisance Call Blocking
---------------------------------------
 *57 !  1157 ! Customer "Trace"
---------------------------------------

Note: These command codes may vary from BOC to BOC. The codes listed above
were found in a general description of CLASS and did not specify a particular
implementation of these services.


Acknowledgements:

Mark Tabas for his views on various included topics... for example, subscriber
tracing ("FUCK NO").
Doctor <413> Who
Mr. DNA

 
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