The Hacker's Encyclopedia 1998

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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/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 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