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:
/--X
CO-2
ESS#
/----I-T-G-----1A-----I-T-G----X
| X--/ |
| | |
| LCCIS |
| | |
| ---------- |
/--X--LCCIS--|CCIS/SPC|--LCCIS--/--X
CO-1 ---------- CO-3
ESS# ESS#
-1A----interoffice trunk group---1A-
NPA - Dial 1223 213 NPA (GTE) - Dial 114
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 n