The CLASS Struggle
We have obtained internal documents from Bellcore which go into some detail on CLASS services that are being offered around the country. Because these services are of growing concern to our readers and much of the population, we will share this information here.
Caller ID is referred to here as Calling Number Delivery (CND), "a revenue-producing service intended for residential and business telephone customers."
"When CND is activated on a line, the DNs [directory numbers] of terminating calls are transmitted to the called CPE [customer-premises equipment]. For an interoffice call [calls between two different central offices], the caller's DN is transmitted from the originating Stored Program Controlled System (SPCS) to which the calling party is connected, to the terminating SPCS to which the called party is connected during call setup. It is then transmitted from the terminating SPCS to the CPE during the first long silent interval of the ringing cycle [between the first and second rings]. A long silent interval is defined as an interval of silence lasting 3 or more seconds. For an intra-office call [calls within the same central office], the caller's DN is retrieved from SPCS memory for transmission to the CPE. Then, depending on the options offered by the CPE, the DN is displayed and/or printed out. The CPE might also be arranged to store the DN for later retrieval by the customer. These options are transparent to the SPCS, i.e., the SPCS performs the same actions for each case. For both interoffice and intra-office calls, transmission of CND data from the terminating SPCS to the CPE should never take place while the CND customer is in an off-hook state.
"Finally, CND service allows the called CPE to receive a 4-digit or longer Personal Identification Number (PIN) instead of the calling DN. The PIN would be dialed by the calling party as part of the calling sequence. Receiving a PIN would indicate that the call is from someone that the called party probably wants to talk to, even though the call might be from a line having a DN that would not have been recognized if displayed to the called party (e.g., a coin line).
"In each of these cases, the data transmission is provided via a simplex voiceband digital interface (VDI). Requirements for this interface are defined in TR-TSY-000030, SPCS/Customer Premises Equipment Data Interface.
"... Although not offered initially, it might be desirable in the future to provide an interface to Directory Assistance or another database so that the calling party name instead of the calling DN can be determined and transmitted to the called party's CPE for display.
"If possible, an attempt should be made to retrieve a partial calling line DN (e.g., less than seven digits for intra-NPA calls, less than ten digits for inter-NPA calls) if the complete DN is not available due to a lack of Common-Channel Signaling (CCS) connectivity. If a partial DN is determined, it should be transmitted to the CPE. The NPA portion of a partial DN should always be included in the transmission to the CND customer's CPE, even if the call is intra-NPA. If neither a partial DN nor a complete DN is available, an out-of-area/DN-unavailable (O/U) indicator, signified by the letter '0', should be transmitted to the customer.
"The following describes responses to irregular user action during activation of CND.
"The customer may dial an incomplete, nonexistent, or erroneous feature activation or deactivation code when attempting to enable or disable this service. If the activation or deactivation code dialed for CND is incomplete or nonexistent, the customer should, as a minimum, be given reorder tone. However, it Is desirable in this case to give the customer a voice announcement explaining the situation encountered. If the dialed code exists but is not the correct code for the service, another service may be inadvertently accessed. This would occur if the customer's line is allowed access to the service associated with the dialed code. To lessen this problem, customers attempting to access the CND service should be given a voice announcement verifying that the service has actually been accessed.
"If a CND activation or deactivation code is dialed by a subscription customer, then reorder tone should be given.
"Similarly, when dialing the activation or deactivation codes for CND, the customer may also request activation of the service while the service is already active, or request deactivation when the service was previously disabled. In these cases, it is desirable to provide an announcement explaining to the customer that the service was already activated or deactivated, as the situation requires. If this is not feasible, the customer should be given a confirmation tone.
"The allowable data transmission rates for this service are given in TR-TSY-000030. It is desirable that a rate of 1200 to 1800 bits per second be provided for this service.
"... CND uses CCS [Common-Channel Signaling] to transmit the calling line DN from the originating SPCS to the terminating SPCS. The protocol used by this feature should be Signaling System Number 7 (SS7), as specified in TR-NPL-000246, Bell Communications Research Specification of Signaling System No. 7. This feature should be capable of functioning on an intra-office basis if the office is not served by a CCS network.
"Originating offices equipped with SS7 should include the calling DN in the address information field within the calling party address parameter of the Initial Address Message (IAM) for all BOC [Bell Operating Companies] and intra-LATA interoffice calls placed over trunks served by SS7. In addition, if the calling party address is a private number or is a DN from a line having the calling number privacy feature active, the presentation indicator field in the Calling Party Number Parameter of the IAM should be set to '0 1' (i.e., 'presentation restricted'). A terminating office should expect to find the calling party address in the IAM if the intra-LATA call setup path does not involve an interexchange carrier and is served entirely by SS7. TR-TSY-000317, Switching System Requirements for Call Control Using the Integrated Services Digital Network User Part (ISDNUP) states that the calling DN is a required field in the IAM.
"... CND is not available on operator-handled calls.
"Special customer-initiated testing does not have to be provided; the customer is normally able to determine if this service is operating correctly when an incoming call is received. However, it is a desirable option to allocate a ON within each SPCS equipped for CND (the DN to be specified by the telco) that the customer can dial to receive a sequence of test data messages. This gives the customer a more positive testing mechanism and can prevent some customer trouble reports. If this customer testing capability is to be provided, the customer should be able to dial the special DN, hang up, and receive a series of test data transmissions designed to check the capability of transmitting any digit in each position. The first test message should begin within 10 seconds of the customer disconnect and should contain the pattern '0123456789'. The remaining nine messages should rotate each of the digits (0 through 9) in each of the digit positions. Two additional test messages should transmit the letters 'P' and 'O', respectively."
All of this only scratches the surface. There will be many more details to reveal. You can obtain a free listing of Bellcore documents by calling 800-521-CORE and asking for document SR-TSY-000264.
Caller ID decoders are new available to hackers in kit form International Micropower Corporation (800-992-3511) sells the IMC-CID-1K for $38. It decodes the Caller ID datastream and converts it to the RS-232C serial format MS-DOS software is available for $6.50 that displays and logs all data to disk. The unit (also available assembled for $45.50) is much less expensive and similar to commercial PC-compatible Caller ID decoders costing hundreds of dollars. This device allows you to actually study the actual binary datastream.