The Hacker's Encyclopedia 1998

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I receved the following documment from a friend who was then a TSPS operator, one year ago -- just before LA cut over to the ACTS/SSAS system. In light of some recent discussion over automated coin telephone service, and automatic calling card service as well, I am submitting it to the list. ><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><><>< HANDLING COIN TOLL CALLS --AUTOMATICALLY - - - - - - - - Automated Coin Toll Service handles the routine aspects of coin-paid toll calls, freeing operators to deal with more complex customer interactions. By James O. Hardy, Dattatraya G. Raj-karne, and Kenneth A. Raschke "Sixty cents, please. Please deposit 60 cents for the first three minutes". The message is familiar, the voice is invariably pleasant and cheerful. What you may not know, however, is that the "operator" at the other end is not human-- it's a machine. By taking over the routine tasks associated with handling coin toll calls, this machine frees operators to concentrate on more complex calls, such as collect or third party billing, and to help any customers who may require assistance. Automated Coin Toll Service (ACTS) is the feature that makes it all possible. ACTS automatically computes charges on coin toll calls, announces charges to the customer, counts coin deposits, and sets up coin calls--all without the need for an operator. ACTS was developed for use with the Traffic Service Position System--an "electronic switchboard" that, since 1969, has been helping operators handle toll and other calls requiring assistance. Today, The Traffic Service Position System--known as TSPS--serves about 90 percent of the Bell System's coin-paid toll calls on an average business day. Automated Coin Toll Service works with TSPS to eliminate or reduce operator tasks on many of the coin-paid calls. ACTS can also make announcements for some non-coin operator-assisted calls. For instance, when a customer requests time and charge quotations, the operator indicates this to the TSPS processor; then at the end of the call, TSPS instructs ACTS to make the appropriate announcement--for example, "The charges are three dollars and 30 cents plus tax for seven minutes". Also, if a customer asks to be notified after a specified amount of time, the operator inputs the specified time to the TSPS processor. Then, at the correct time, TSPS instructs ACTS to make an announcement, such as "Six minutes has ended". When a customer makes a station-to-station toll call from a coin telephone, the local central office routes the call to its associated TSPS. In areas served by Automated Coin Toll Service, the TSPS central processor connects the call to the Station Signaling and Announcement Subsystem (SSAS) hardware that provides Automated Coin Toll Service. SSAS is an "intelligent peripheral" subsystem, receiving instructions from and sending data to the TSPS central processor. SSAS TAKES OVER TSPS provides information to SSAS about call charges and the length of the initial period for the call. Using this information, SSAS constructs and sends a series of announcements to the customer. The first gives The initial charge for the call. The customer might hear, for example, "One dollar and 20 cents please [two second pause] please deposit one dollar and 20 cents for the first three minutes". If the customer deposits a coin during the initial request, the announcement is truncated immediately. This announcement allows a customer to deposit the required amount without listening to the entire deposit request. As the customer deposits money, SSAS detects each coin signal, and totals the amount deposited. When the correct amount has been deposited, SSAS returns control to TSPS, which completes the call connection. If the customer deposits too much, SSAS tells the customer that the additional money is credited toward overtime. Should the customer fail to deposit enough money within a reasonable time, SSAS generates a prompting announcement. If no money is deposited after the prompting announcement, TSPS adds an operator to the connection. A customer can also reach an operator by flashing the switchhook. If the customer is still using the phone at the end of the initial period-- usually three minutes--TSPS again connects SSAS to the call, and orders it to tell the customer that the initial period has ended. If the customer talks beyond the initial period and then hangs up, TSPS rings back. When the customer picks up, TSPS instructs SSAS to request overtime charges, and to monitor coin deposits. If the customer talks for a long time after the initial period, TSPS periodically instructs SSAS to request and collect interim deposits as well. In short, with Automated Coin Toll Service, SSAS performs two major functions previously requiring operators: It provides announcements to the customer, and it monitors coin deposits. To provide these functions, SSAS relies on three principal components: a number of Coin Detection and Announcement circuits to connect customers to SSAS; a control unit to coordinate the sending of voice signals over those circuits and to interface with the TSPS processor; and a solid-state announcement store to hold digitized voice signals. Sample dialog Customer ACTS/TSPS Picks up handset Dial-tone (from local office) Dials number "One dollar and 20 cents please. [pause] Please deposit one dollar and 20 cents for the first three minutes". Deposits $1.10. Drops dime "Please deposit 10 cents on floor and searches for more". six seconds. Gives up search and "Thank you. You have 15 deposits quarter. cents credit toward overtime". Talks for three minutes. "Three minutes has ended. Please signal when through". Talks for two more Ringback of calling phone. minutes and hangs up. Picks up handset. "Twenty-five cents please. [pause] You have 15 cents credit. Please deposit 25 cents more for the past two minutes". Deposits 25 cents. "Thank you". Hangs up. CONNECTIONS Coin Detection and Announcement (CDA) circuits provide the link between the customer at the coin station, and the control unit of the Station Signalling and Announcement Subsystem. Each CDA circuit can convert digitized speech from the announcement store into analog voice announcements. In addition, each CDA circuit contains a data receiver to detect coin-deposit signals generated by the coin station; different signals distinguish nickel, dime and quarter deposits. An individual CDA circuit handles just one call at a time. The number of CDA circuits needed to handle coin toll calls for a TSPS office can therefore vary widely from one location to another. Presently, each SSAS can handle a maximum of 239 announcement circuits. Normally, though, only 30 to 100 CDA circuits are needed to handle coin toll traffic, even in large metropolitan offices. The additional circuit capacity is available for use in the future to provide new automated TSPS services. MICROPROCESSOR CONTROL The SSAS control unit contains its own microprocessor, or programmable controller--the "intelligent" part of SSAS. The programmable controller handles the internal control-unit operations and, together with other circuitry, transfers voice data bits from the announcement store to the CDA circuits, and communicates with the TSPS processor. Because of its central role in the control unit, the programmable controller has several self-checking capabilities. Some functions within the controller are duplicated, so that errors can be detected by comparing the controller outputs. The control unit also checks for errors in the program instructions by examining special binary digits called "parity bits" at the end of each "word" of instruction. Wherever a programmable controller error is detected, TSPS is notified so that the appropriate fault recovery actions can be taken. When a customer starts to make a coin-station call, TSPS instructs the control unit to make an initial announcement to the customer over a specified CDA circuit. TSPS provides the control unit with information about the required deposit and the length of the initial call period. Using this information, the control unit determines the appropriate announcement, and begins to retrieve, sequentially, the required data from the announcement store. The announcement store data are converted into a digital serial bit stream and transmitted to the specified CDA circuit. Here, the serial bit stream is converted into an analog signal, and the resulting announcement routed to the customer. As the customer deposits coins in response to announcements, the control unit interrogates the CDA circuit for coin-deposit information. The control unit totals the coins deposited and, when the amount paid matches the amount required, acknowledges the correct deposit with a "Thank you". When appropriate, the control unit initiates an announcement requesting additional money or acknowledges credit for overdeposits. Finally, the control unit notifies TSPS when the deposit is satisfactory--or, if the customer has not deposited the coins quickly enough, that TSPS should connect the customer to an operator. To ensure that ACTS will serve customers most effectively, and to encourage customers to deposit coins promptly and accurately, a good deal of attention has been directed toward the customer-machine interaction. Announcements must be intelligible, carefully worded, and appropriately timed. So a human factors study was conducted in 1975 with the cooperation of Illinois Bell in Chicago, to aid in determining an efficient set of phrases, sentences, and timing parameters for the machine-generated ACTS announcements. SPEECH SEGMENTS ACTS announcements are constructed from a set of 512-millisecond "speech segments". Each segment is equivalent to about one word of the ACTS vocabulary. Under the direction of the control unit, individual words or word segments are retrieved from the announcement store and strung together to form announcement phrases and sentences. Most words, such as "cents" or "minutes" require a single speech segment; some words, such as "fifteen" and common phrases such as "Please deposit" require two speech segments. A few phrases such as "Please signal when through" require three speech segments. Each phrase involving two or three speech segments could have been formed by stringing together the appropriate individual words, each encoded as a separate 512-millisecond speech segment. More natural sounding speech results, however, if the phrase is treated as a complete unit requiring one or one-and-a-half seconds of encoded speech--that is two or three contiguous speech segments. The vocabulary of about 80 words presently required for ACTS announcements was initially recorded by a professional announcer. The words were then digitally encoded using a process called Adaptive Delta Modulation and organized into eighty 512-millisecond segments. Each segment (word) or group of segments (long word or phrase) was adjusted to a consistent level and pitch with silent periods inserted where needed. This results in natural-sounding speech when the segments are joined together in various combinations to form sentences. To store announcement speech segments, SSAS uses the same type of semiconductors memory that is currently used by the TSPS central processor. Each 512 millisecond speech segment requires that 16,000 bits of information be stored, grouped into 400 individual "data words". A data word contains 47 binary digits or bits; 40 of these are for announcement data, and seven for error checks. The announcement store must serve a maximum of 239 CDA circuits simultaneously- even releasing the same speech segment to all circuits at the same time if necessary. But the store is equal to the task: It can release the data at the rate of eight million bits per second--equivalent to 40 bits of data every five microseconds. This rate ie 256 times the speed at which digitized speech segments are decoded by each CDA circuit and converted to analog speech. Consequently, designers devised a "time multiplexed" arrangement whereby the announcement store retrieves one 40-bit data word every five microseconds, and distributes that data word to any one of 256 circuits. Of these, 239 are for CDA service to customers, and 17 are for diagnostic and fault testing. It takes 1.28 milliseconds to distribute a data word to each of the 256 circuits in sequence. Four hundred repetitions of the distribution sequence release 400 40 bit data words to each circuit every 512 milliseconds. This is precisely the rate required to produce simultaneous, uninterrupted announcements, each consisting of several 512-millisecond segments joined together. Although the vocabulary required for coin traffic might appear to be constant, it can in fact change. This is because call-handling practices sometimes change, and because any future developments for Automated Coin Toll Service may require vocabulary changes or additions. Also a significant number of words will be needed as new automated features are added to TSPS. The capabilities of the SSAS random access memory permit vocabulary changes to be incorporated readily, and permit expansion of the vocabulary to include up to 480 speech segments. RELIABILITY Because Automated Coin Toll Service must be highly reliable, parts of the SSAS hardware are duplicated. Several sophisticated techniques detect faulty operation, evaluate its seriousness, and then bypass or remove the faulty part from service at the most appropriate time. For backup in case of failure, SSAS has two identical control units and announcement stores. One control unit and its dedicated announcement store constitute the "active" side and handle all calls; the other control unit and announcement store are called the "standby" side. The standby side is made active when the other side fails. Extensive self-checking and fault-detecting capabilities within each side allow many operations to occur independently, minimizing interaction and common circuitry between the two sides. Consequently, there are very few single hardware faults that can cause both sides of SSAS to fail simultaneously. If such a fault does occur, only those calls currently being handled by ACTS are lost or interrupted; subsequent coin calls are routed to operators until ACTS is restored. Although only the active side of SSAS handles calls, the standby side must keep an up-to-date copy of data associated with each Coin Detection and Announcement circuit. Should a problem develop on the active side, the standby side will need this information to take over call processing. The active side, therefore, continuously sends updated call-related information to the standby side. TSPS's basic fault-recovery mechanism is a switch to the standby side when a fault is detected. There are three ways to do this: with a smooth switch, an immediate switch, and a rough switch. A smooth switch is used when the active side has a fault that does not seriously affect call processing. For example, a single bit failure in the announcement store can be tolerated until the switch to standby is convenient, since its impact on announcement quality is insignificant. Before switching, TSPS first brings the two sides into approximate synchronization, with the standby side running just behind the active side. The switch is then imperceptible to customers. An immediate switch is made whenever the active side develops a serious fault, such as control-unit failure, while the other side is on standby. Since the standby memory is up-to-date, only minor disruptions in call handling can result. For example, an announcement might be interrupted and, after approximately half a second, repeated in full. A rough switch is necessary whenever the active side develops a fault while the other side, normally on standby, is running diagnostics. When TSPS detects a serious fault with the active side, it immediately takes that side out of service, halts the diagnostics, and forces the standby side to become active. Since the memory of the newly active side is not up-to-date, any calls being handled when switching occurred are lost or interrupted. The chance that this might happen, though is very small. BENEFITS Automated Coin Toll Service is helping to reduce the Operating Company cost of handling routine toll calls. It also monitors coin deposits with greater accuracy than before, and helps Operating Companies detect trouble at coin stations. Automated Coin Toll Service was first installed in Phoenix Arizona, in 1977. Since then, a rapidly growing number of the Bell System's 146 TSPS sites have introduced ACTS. By the mid-1980s, Automated Coin Toll Service is expected to be available for more than 95 percent of all Bell System coin statios. At that time, freed from handling more than two million routine coin toll calls a day, operators will be better able to help those customers with more demanding and complex problems--problems that truly require human skills..