337 lines
17 KiB
Plaintext
337 lines
17 KiB
Plaintext
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Custom Local Area Signalling Services
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Written by: The Videosmith
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Version - 1.1
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----------------------------(c) Copyright 1994---------------------------
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This article will explain the newly developed LASS system (AT&T Bell Labs),
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and how it may affect us in the near future. Note that the service as it
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appears for customers is called "CLASS", the C standing for Custom. I
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assume this is just for looks.
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LASS
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----
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The telephone was destined to become a well used and powerful tool for
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otherwise tedious tasks. Gas meters and other metered services would be
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surveyed through the use of automatic data retrieval employing telephone
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communications. All in all, some have big plans for the uses one could put
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the telephone system up to, and CLASS is one plan that is going to drop an
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innovative bombshell on the telecommunicating world.
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At this moment, a local CCIS network feature is being developed by Bell
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Laboratories. This feature will change the way people use fones, and will
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also change the attitude in which they use them. It will give far more
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control of the telephone to the user than ever before. This feature is
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called CLASS (Custom Local Area Signalling Services).
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Everyone will find something useful in this newly developed telephone
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feature. Pizza parlours will no longer have to worry about fraudulent
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italian food mongers, and little old ladies won't have to worry about prank
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calls by certain dubious characters.
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What are all these fantastic features? These features will include call
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back of the last caller, regardless of whether you have their telephone
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number or not. Another will be distinct call waiting tones, and preselected
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call forwarding (only those people whom you wish to speak to will be
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forwarded). This is a rudimentary list of CLASS features to come. It is a
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very powerful system, and it all relys on LCCIS (Local Common Channel
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Interoffice Signalling), an intra-LATA version of the ever-popular CCIS.
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CCIS Background ---------------
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CCIS was originally introduced in 1976 as, basically, the signalling
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system to end all signalling systems. Instead of using the voice grade
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trunks to carry signalling information on, a data network would be used.
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This network is comprised of data links from each TO [involved with CCIS]
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to the appropriate STP (signal transfer point). Signalling information is
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sent through these links at 4800 bps to the STPs (Note that baud rates may
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increase due to the economic availability of faster data communications
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hardware), where stored program control routes the signalling information
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to the needed offices in order to open and complete the call path. SPC
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checks automatically for on-hook/off-hook status before opening the path,
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and if the status is off-hook (in this case the customer does not have the
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call waiting custom calling feature), returns information to the
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originating CO to apply a busy signal to the customer. This is but one of
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many features toll CCIS provides the network with.
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Since this text is not centered on the topic of toll CCIS, technical
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aspects aren't as important (except for the comparison between the local
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and toll networks for observational purposes): yet it is important to
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notice how automated and flexible this type of signalling method is, as
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well as its speed and efficiency. All the software control involved with
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local and toll networks is called, fittingly, the "stored program control
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network." or ISDN (Integrated Services Digital Network). LCCIS will be
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addressed in a future article.
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CLASS/LCCIS Features --------------------
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LCCIS would look like this:
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/--\
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CO-2
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ESS#
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/----I-T-G-----1A-----I-T-G----\
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| \--/ |
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| LCCIS |
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| | |
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| ---------- |
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/--\--LCCIS--|CCIS/SPC|--LCCIS--/--\
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CO-1 ---------- CO-3
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ESS# ESS#
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-1A----interoffice trunk group---1A-
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\--/ \--/
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SPC = Stored Program Control (Network control and Signal Transfer Point)
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ITG = Interoffice Trunk Group
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Using a high-speed data link between local offices creates a much more
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flexible and more effecient way for intra-LATA central offices to communi-
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cate. Instead of using per-trunk signalling (using the same trunk used for
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voice transmission to send routing and billing information), such data
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would be sent thru a 2400 bps dedicated data link, which interacts with a
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local signal processing and transfer point. From that point, signalling
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information is distributed to appropriate central offices or tandem
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switches.
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At the time during which this article was being initially researched, CLASS
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was only being developed for the #1A ESS switch due to the flexibility of
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it's memory handling, it's speed and what Bell Labs called 'cost
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efficiency'. At the end of the research involved with this article, CLASS
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was already implemented in data stage on ESS#5.
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LCCIS will work with the local switches using stored program con-trol,
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keeping track of call data. The 1A switches will use what is called
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"scratch pad" memory (also known as call store), in conjuction with LCCIS's
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database, to accomplish all the features that LASS provides. This memory
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will hold such data as "line history", and a "screening list". That
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information will make it possible for autoredial, selective call
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forwarding, nuisance call rejection, and distinctive call waiting tones.
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Selective CF ------------
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Selective call forwarding is defined by the subscriber (the sub-scriber
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must have conventional call forwarding to request this service). Using
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call store, or more specifically the screening list, one will be able to
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selectively forward a call to another directory number by executing a few
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simple commands on the friendly home-bound telephone (unlike migrating
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telephones most frequently found in hotel rooms). An access code (a list
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will appear at the end of the file) will be entered, and a special tone
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will be issued from the subscriber's CO. The cus-tomer will then dial in
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the numbers he wants forwarded to the particular number. After each number,
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a tone will sound indicating the acceptance of the number. Individual BOC's
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(Bell Operating Companies) will be able to define the amount of numbers
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which may be screened. Once this is done, the cusomter hangs up and the ESS
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takes over. Now, whenever some one calls this particular customer, the
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customer's switch will compare the calling line's directory number with
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those stored in scratch pad memory. If the CLID matches one of the numbers
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in 1A memory associated with the called directory number, the number is
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forwarded. If not, the phone will ring at the original destination. This in
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particular could make it very difficult on system hackers, as you could
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probably imagine. A company can subscribe to this CLASS feature, and enter
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only the numbers of authorized users to be forwarded to a computer. Bureaus
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inside the various telephone companies and other sensitive operations can
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screen calls to particular numbers by using this service.
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This is a security that's hard to beat, but of course there is a way
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(simple law of nature: nothing is fail-safe). There will always be the
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obvious way of finding numbers which are being forwarded to, like auto-
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dialing entire exchanges (one after the other). Unfortunetly, CLASS will be
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providing other services which might make "scanning" seem less attractive.
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Distinctive Ringing
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-------------------
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Distinctive ringing is handled in the same fashion as selective call
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forwarding is: the screen list in scratch pad memory. The customer may
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enter numbers which the ESS should give special precedence to, and when-
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ever a call is placed to this particular customer's number, ESS checks to
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see whether the CLID matches a directory number listed in the switch's
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memory. If a match is made, the subscriber's CO gives the off-hook line a
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special call waiting tone, or the on-hook phone a distinctive ring
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(possibly using abnormally timed ringing voltage... some readers may
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picture a British Telecom ring as an example, although many foreign audible
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rings tend to be different).
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Call Rejection
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--------------
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Nuisance call rejection, a feature making it possible to block certain
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idiots from ringing your fone (a feature we can all benefit from at one
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time or another... or all the time), uses the information retrieved from
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LCCIS (CLID). Let's say customer A calls customer B:
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----LCCIS----
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A ---> CO< >CO ---> B
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----trunk----
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Customer B happens to despise customer A, and keys in a special *##
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code. ESS again takes over and looks at the CLID information, and stores
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the calling line directory number in a special screen list associated with
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with customer B. The next time customer A tries calling customer B, the
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terminating office will reroute the call to a local (the originating CO)
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digitized recording telling customer A that the call he made cannot be
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completed due to customer B's request ("I'm sorry, but the customer you
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have tried to reach wishes you were eaten by a rabid canibal on drugs").
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Dial Back
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---------
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To create such a feature as "dial back" (for called or calling party),
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the ESS scratch pad memory is used again. The same principles are used as
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are employed in the already established custom calling feature, auto-
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redial. CLID will be used in this way:
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(received from CLID)
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last-called-mem last-caller-mem
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---------- ----------
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|###-####| |###-####|
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---------- ----------
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Your ESS switch will keep track of who you called last, and who called
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you last, thru the retrieval of calling line information provided by LCCIS
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in conjunction with your switch (Your switch will know what number you
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called last by directly storing the digits you dialed previously. Local
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signalling will provide calling line information via LCCIS call information
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forwarding using the data link mentioned). This way, with your access code
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(*##), you will have total re-dial service.
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Customer Trace
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--------------
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This type of memory handling and signalling method will also allow the
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feature that everyone was afraid would abolish "phreaking". Subscriber
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initiated tracing, using the last caller directory number stored at your
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CO, will be available as far as Bell Laboratories is concerned. There seems
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to be two types of "customer originated trace". One will forward the number
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to local authorities, at which it will be handled through the police. The
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other feature AT&T/Bell Labs is working on will be a display module that
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will sit by your fone, and will display calling directory numbers. All
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other CLASS features that use the calling line information are used at the
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descretion of the caller. The customer originated trace, however, using the
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individual or bulk calling line identification features ("trace") allow the
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customer to view the calling number. The world is not ending... yet, in any
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case. Individual customers will be able to employ a special "privacy code",
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which when dialed, tells the far-end switch not to forward the calling
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number to a desk display. Whether there will be a way to override this or
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not is obvious: of course. The police, the military and government
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agencies are all likely to have a higher priority level than your privacy.
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It seems that long distance carriers could benefit greatly from CLASS. Why
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Bell/AT&T should give any type of special services to OCCs not given to
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other non-telephone companies, especially after equal access is fully
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implemented, I don't know (but then again, it is EQUAL access). It's always
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possible. It is also possible that there will be no desk display. There are
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those phone phreaks who feel that BOC's will never give the end party the
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priviledge of retrieving the calling party's number directly, if not due to
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plain old Bell policy on the issue of privacy. We'll have to wait and see
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about that point: the desk display is, in fact, operational and is being
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used in test stage. Whether Bell Labs feels that this feature can and will
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be used in a full scale non-beta stage BOC situation is a different story.
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The economic feasability is questionable.
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End Notes
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---------
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CLASS, using local CCIS, will not function on inter-LATA calls. The
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local CCIS network is exactly that: local, and does not extend into the
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realm of "toll network". This will eventually be corrected (allowing toll
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CCIS to interact with LCCIS as far as CLID information is concerned). How
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the various long distance networks will exchange information with the local
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BOC network has not been determined [by the writer of this article]. It
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would seem like a monumental task to try to integrate the emerging long
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distance companies into the AT&T/BOC ISDN, be it because of equipment
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inconsistancies or lack of cooperation on the part of the OCC, etc. This
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will be discussed in an upcoming article dealing with toll CCIS. Although
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CLASS has been built around the ESS #1A switch, it has, as has been
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mentioned, been co-developed for use with the ESS #5 switching machine.
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CLASS is going to cause problems, as well as create a new environment
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for telephone users. Of course, those problems are only problems to people
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who will generally be reading this article, but the more you know about
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CLASS the more comfortable you'll feel about the service. It can be used to
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one's advantage, even as a telecommunications hobbyist. Just as a
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corporation will be able to set up a complete history of who is calling
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their system, and eventually keep people off the system using the screen
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list in memory, the same features can be applied to bulletin board systems
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and the like. Imagine being able to keep all the local bozos off your
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board, or being able to screen all but your private local users (making
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your system completely inaccessible through the PSTN network from any
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telephone but that of one of your users). It would seem to be a useful
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feature, if nothing else but an easy feature, to implement.
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It is a little difficult, if not plain awkward, to write an article
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about a topic which is subject to change at the researcher's ignorance. I
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think that CLASS is enough of a momentous issue that at least some text by
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a hobbyist should be released for public knowledge purposes. Yet my
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awareness of the fact that some of this text may be outdated, or
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inaccurate, by the time CLASS is released as a BOC service, is in itself
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the explanation of why there is a version number at the head of this
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article. Most likely, when CLASS becomes public, the second version will be
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released with update notes (if need be...most probably so). I hope you
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enjoyed it,
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The Videosmith. LOD/LOH!
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---------------------------------------
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Test stage defaults for some features:
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DTMF ! Pulse ! Description of Service
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---------------------------------------
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*66 ! 1166 ! Reconnect last caller
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---------------------------------------
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*63 ! 1163 ! Selective Call Forward
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---------------------------------------
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*60 ! 1160 ! Nuisance Call Blocking
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---------------------------------------
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*57 ! 1157 ! Customer "Trace"
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---------------------------------------
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Note: These command codes may vary from BOC to BOC. The codes listed above
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were found in a general description of CLASS and did not specify a particular
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implementation of these services.
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Acknowledgements:
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Mark Tabas for his views on various included topics... for example, subscriber
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tracing ("FUCK NO").
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Doctor <413> Who
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Mr. DNA
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Downloaded from Just Say Yes. 2 lines, More than 500 files online!
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Full access on first call. 415-922-2008 CASFA
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Another file downloaded from:
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!
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-$- & the Temple of the Screaming Electron
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! * Walnut Creek, CA
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+ /^ |
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! | |//^ _^_ 2400/1200/300 baud (415) 935-5845
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/^ / @ | /_-_ Jeff Hunter, Sysop
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|@ _| @ @|- - -|
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| | | /^ | _ | - - - - - - - - - *
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|___/____|_|_|_(_)_| Aaaaaeeeeeeeeeeeeeeeeee! /
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Distributed in Europe by:
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