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(>-------------------------------------
--------------------------------------<
)
The LOD/H Technical Journal: File #2
of 13
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/S
PC--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 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
(>-------------------------------------
--------------------------------------<