STATE CONTROL FOR A REAL-TIME SYSTEM UTILIZING A NONPROCEDURAL LANGUAGE

Abstract: A software system written in a nonprocedural language for controlling a telecommunication system in which an internal software signal is generated when a state is exited and another internal signal is generated when a state is entered to control common operations for the state transitions. For each state, a group of instructions written in the nonprocedural language is autonomously executed in response to the exit signal to perform common exit operations for that particular state. A second group of instruction is autonomously executed in response to the entrance signal to perform common entrance operations for that particular state. Various services performed by the telecommunication system are written in scripts of groups of instructions called triples. Each triple has an event definition defining the signal that the triple will respond to and a state definition defining the state in which the system must be in before the triple can respond. Programmer productivity is increased because when new features are added, the common operations previously performed on exiting and entering a state will continue to be performed plus the programmer can add new functions to be performed upon the entrance or exiting from a state without detailed knowledge of the program implementing the previous services.

Description: This invention relates to a method according to preamble of claim 1. According to the preamble of claim 8, the invention relates further to an apparatus for carrying out the method of claim 1. State diagrams are commonly used to define the operations of real-time processes. When a computer system that is executing a language, such as C or Pascal, is being used to control the operations of the real-time process, the program has one set of instructions for each of the possible states and the signals that can be received in those states. While in a given state, the instructions are sequentially executed upon the receipt of individual signals to perform the required control functions. The computer's response to process signals is implicit from the sequence of instructions. There are languages wherein the states and process signals are explicitly defined, and in which the occurrence of these states and signals causes the execution of specific action instructions. One such language is described in the article by J. M. Ginsparg and R. D. Gorden, "Automatic Programming of Communication Software Via Non-Procedural Descriptions", IEEE Transations on Communications, Vol. COM-30, No. 6, June 1982. This article discloses a programming language for writing programs to control a telephone switching system. Such programs are written in terms of the possible states of the system, occurrences of events within the system, and actions to be taken when defined events and states occur. After program statements are written in that language, they are then translated to the C programming language and compiled and stored within the computer controlling the telephone switching system. Whereas, this language does allow the statements to explicitly designate the actions to be taken in response to a given event, no provision is made for performing common actions that are required upon entering or leaving a state, regardless of individual state transitions. Without provision for performance of such common actions, the resulting programs become complex and difficult to modify. Another approach is the Specification and Description Language, SDL, that is presently being defined by a CCITT committee. The SDL language is described in the article, "SDL-CCITT Specification and Description Language," IEEE Transactions on Communications ," Vol. Com-30, No. 6, June, l982, by A. Rockstrom and R. Saracco, and the CCITT specifications are set forth in Recommendations Zl0l-l04, CCITT Yellow Book , International Telecommunication Union, Geneva, Switzerland, l98l. The SDL language allows a formal description of services and features in terms of state and telecommunication signal information. Manufacturers of telecommunication systems then implement that formal description in the language of their choice, such as CHILL or C. The SDL description itself is not directly compiled. In addition, SDL does not provide for the execution of common actions upon entering or leaving a state. As previously noted, a problem common to both of the prevously mentioned prior art methods of utilizing state diagrams in real-time process control is the performance of actions that must commonly be done upon leaving a state and entering a new state, regardless of the particular transition involved, (i.e., the event that motivated the transition). An example of such an action occurs in a telephone system where a customer's telephone is being rung, e.g., it is in the ringing state, and the customer goes off-hook, e.g., an off-hook signal is received. The required actions are to remove the audible ringing indication from the customer's telephone, and upon entering the next state, e.g., talk state, to establish a voice connection to the calling telephone. In simple telephone service, often referred to as plain old telephone service (POTS), the problem is reasonably easy to solve since the possible ways of going from the ringing state to the talking state are well known at the time of programming POTS service. Problems arise at a future time when it is desired to add new telephone features that will interact with POTS in unforeseen ways. In the prior art programming techniques, the programmer writing such new features needs to fully understand the original code and the interaction of his or her new code with the original code in order to determine all of the ways under which a state could be entered or left. This requirement not only delays the introduction of new features, but makes maintenance of existing programs more difficult. From the foregoing, it can be seen that there exists a need for a software mechanism that will assure that certain specfied actions are taken each time a new state is entered and each time a state is left regardless of the circumstances under which those events occur. Such a mechanism would perform the required operations upon entering the state and the required operations upon leaving the state. In addition, the execution of these required operations should require no additional program statements in any new features being added or even the programmer's knowledge of how these operations are performed. Yet, the programmer should have the ability to modify and add to these operations. The foregoing problems are solved by the characterizing features of the independent claims. Preferred embodiments of the invention are claimed by the subclaims. Advantageously, the voice and data telecommunication system has a plurality of states and a plurality of signals that cause state transistions, and a computer controls the system by executing a program comprising a finite state machine routine and sets of groups of instructions with each set providing a feature on said system and each group responsive to a predetermined system state and signal for actuation. The execution of an instruction in a first group of instructions initiates a change from the present state to the next state. The finite state machine routine is responsive to this state transition to generate a leave signal indicating an exit from the present state and an enter signal indicating an entry into the next state. A second group of instructions is responsive to the leave signal and the present state to perform common exit operations to condition the telecommunication system for the termination of the present state. A third group of instructions is responsive to the enter signal and the new state to perform common entrance operations that initialize the telecommunication system for the new state. Advantageously, in order to promote the latter addition of new features to the system, the second group of instructions controls whether another group of instructions is allowed to respond to the leave signal by executing an instruction which either allows the finite state machine routine to continue the processing of the leave signal or terminates this processing. If the processing is continued, a fourth group of instructions is responsive to the leave signal for performing additional common exit operations. If the processing of the leave signal is terminated, the finite state machine routine then begins to process the enter signal. Similarly, each group of instructions responsive to the enter signal can control whether other groups of instructions responsive to the enter signal and the next state are allowed to respond to these conditions. The foregoing and other objects, features and advantages of the invention will become more apparent from the following and more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings, in which: Fig. 1 illustrates, in block diagram form, the telecommunication system that is the subject of this invention; Fig. 2 illustrates, in state diagram form, the states of a customer unit of the telecommunication system of Fig. 1; Figs. 3 and 4 illustrate a program script, in source code form, for providing basic telephone service for the telecommunication system of Fig. 1; Fig. 5 illustrates program scripts for providing call forwarding and calling party identification services with call forwarding activation/deactivation service for the telecommunication system of Fig. 1; Fig. 6 illustrates logical signal tables with the implementation of call forwarding, calling party identification, and basic telephone services for the telecommunication system of Fig. 1; Fig. 7 illustrates the logical signal tables of Fig. 6 upon the call forwarding service having been deactivated; Figs. 8 and 9 illustrate a program script for providing data service for the telecommunication system of Fig. 1; Fig. 10 illustrates, in block diagram form, software processes and interprocess communication that is utilized in the control of a customer unit's computer of Fig. 1; Figs. 11, 12 and 13 illustrate software structures that are utilized to implement the logical signal tables of Figs. 6 and 7; Fig. 14 illustrates block 1206 of Fig. 12 in greater detail; Fig. 15 illustrates the format of a compiled triple that results from compilation of the source code for a triple such as illustrated in Fig. 3; Figs. 16 through 21 illustrate the various instruction formats used in Fig. 15; Fig. 22 illustrates, in greater detail, the accessing of variable and literal values from their associated tables on the basis of information contained in a compiled triple such as the one illustrated in Fig. 15; Figs. 23 and 24 illustrate, in flowchart form, FSM 1005 process of Fig. 10; Fig. 25 illustrates, in flowchart form, block 2314 of Fig. 24; Figs. 26, 27 and 28 illustrate, in greater detail, block 2505 of Fig. 25; Figs. 29, 30 and 31 illustrate, in greater detail, the activation of a program script by giving additional details of block 2315 of Fig. 23; Figs. 32 and 33 illustrate, in greater detail, block 2920 of Fig. 31; Figs. 34 through 37 illustrate, in flowchart form, interpreter 1006 of Fig. 10; Fig. 38 illustrates, in flowchart form, the NEXTSTATE primitive and, in particular, illustrates the processing of the leave and enter signals; and Fig. 39 illustrates how Figs. 11, 12 and 13 may advantageously be combined. The software system which is the subject of this invention is advantageously implemented by the hardware system illustrated in Fig. 1. However, it would be obvious to one skilled in the art that other hardware systems are controllable by the illustrative software system. The hardware of Fig. 1 comprises a plurality of customer units 102 through 103. Each customer unit comprises a computer, a telephone handset and a data terminal. Voice and data information is communicated in the form of packets via bus 100. Bus 100 may be advantageously be of the Ethernet ™ type, or it may be a packet switching system as described in US-A-4,494,230. Customer unit 102 comprises computer 104 and a terminal 106. Computer 104 contains units not shown for interfacing to bus 100, telephone handset 105 and terminal 106, and for performing the analog-digital conversions utilized for transmitting voice information from and to handset 105 via bus 100. During the initialization of the system and as required to implement changes in the operation of the customer units, scripts that are written in the nonprocedural language are entered via a terminal to computer 101. Computer 101 compiles these scripts and then downloads interpretable representations of them via bus 110 to the designated customer unit's memory via that unit's processor. Each script comprises a plurality of triples with each triple comprising a state definition, an event definition and an action definition. The event definition defines which signal actuates the triple and the action definition defines the action to be taken upon the triple actuation. The action definition is made up of a group of instructions. The states and signals that actuate triples for Plain Old Telephone, POT, service are illustrated in FIG. 2. FIG. 2 illustrates in state graphic form, the various states 20l through 208 that one of the customer units l02 through l03 may be in at any particular point in time during a line-to-line call. It would be obvious to one skilled in the art to expand the number of illustrated states to meet new system requirements. In addition, to the signals illustrated in FIG. 2, leave and enter signals are generated each time a state transition occurs. Triples actuated by those signals perform common transitional operations regardless of which signal shown on FIG. 2 caused the state transition. Each script can have any number of triples actuated by either those signals. Signals 2l0 through 224 represent the events whose individual occurrences causes a transition from one state to another state. Again, it would be obvious to one sklled in the art to expand the number of signals to meet new system requirements. For example, in order to place a call, the customer unit must be initially in idle state 20l and go off-hook. The event of going off-hook places the customer unit in dialing state 202 via off-hook signal 2l0. After the digits have been collected from the terminal, the state is changed from dialing state 202 to outpulsing state 203 via digits signal 2ll. In outpulsing state 203, the customer unit being called is sent a request for a call termination. If the called customer unit is busy, then busy state 207 is entered via busy signal 2l7. If the calling customer unit goes on-hook while in outpulsing state 203, or dialing state 202 or busy state 207, then the calling customer unit is returned to idle state 20l via either on-hook signal 2l6, 2l5, or 2l8. If the called customer unit is not busy, then the calling customer unit enters audible state 204 via ringing signal 2l2. While in the audible state, the calling customer unit hears the ringback tone. If the calling customer unit goes on-hook during audible state 204, it is transferred back to idle state 20l via on-hook signal 224. Once the called customer unit answers the call, the calling customer unit is transferred to talking state 205 via answer signal 2l3. Upon entering talking state 205, the calling and called parties exchange voice packets via bus l00. If the called party hangs up first, the calling party is transferred from talking state 205 to disconnect state 206 via disconnect signal 2l9. If the calling party hangs up frst, the calling party is transferred from talking state 205 to idle state 20l via on-hook signal 2l4. Consider the previous example from the point of view of the called station. Upon receipt of a message 223 via bus l00 indicating that another customer unit wants to set up a voice connection, the called customer unit is transferred from idle state 20l to ringing state 208 via origin signal 223. While in ringing state 208, the called customer receives an audible ringing indication. If the called customer unit goes off-hook, it is transferred to talking state 205 via off-hook signal 22l. If, instead, the calling unit goes on-hook while the called unit is in the ringing state 208, it transmits a disconnect signal contained in a message communicated via bus l00. In response to the disconnect signal, the called customer unit is transferred from the ringing state 208 to idle state 20l via disconnect signal 222. Turning now to the invention, a script for implementing the transitions from the various states illustrated in FIG. 2 is illustrated in FIGS. 3 and 4. The script implements plain old telephone (POT) service or basic telephone service in terms of triples. The latter, once compiled, is stored in memory l08 and executed by processor l07. More details of the language utilized in FIGS. 3 and 4 is given in Appendix A. One skilled in the art can observe from FIGS. 3 and 4 that there is no requirement for ordering the triples. The order of execution is explicitly designated by state and event information and an interscript control mechanism that is implemented during the downloading and activation of the scripts and during execution of the triples. Consider the example where customer unit l03 is calling customer unit l02. Customer unit l02 is in idle state 20l of FIG. 2. Upon receipt of a message from customer unit l03 containing an origin signal 223 which designates that a call is to be set up, the origin event of triple 303 matches and thus the triple is actuated. The $SOURCE variable is set equal to the telephone number of customer unit l03 by the compiled code for the event definition. The operations to be executed are specified by the action definition of triple 303. First, the information in the $SOURCE variable is transferred to the $ORIGINATOR variable for later use, and a message containing ringing signal 2l2 is transmitted to customer unit l03 via bus l00 by execution of the SEND primitive to inform customer unit l03 that customer l02 is entering the ringing state. The information in $SOURCE variable is then transferred to $OTHERPARTY variable for later use. The last operation performed is the execution of the NEXTSTATE primitive designating that ringing is to be the next state of customer unit l02. When the state is changed to ringing, the enter signal is generated for ringing state 208. Since the enter signal is generated internal to latter state, it is not illustrated in FIG. 2; but it is explained in detail with respect to FIG. 38. The generation of the enter signal causes triple 305 to be executed. The action definition of triple 305 applies the audible ringing "tone" or "indication" to handset l05. As illustrated in FIG. 2, customer unit l02 leaves ringing state 208 by either going off-hook causing an off-hook signal 22l to be generated or by receiving a disconnect signal 222 from customer unit l03 via bus l00. The disconnect signal 222 from customer unit l03 indicates that unit l03 has gone on-hook. If customer unit l02 goes off-hook, the off-hook signal 22l is generated, and triple 308 is executed. Triple 308 informs customer unit l03 with a message containing answer signal 2l3 that customer unit l02 has answered. In addition, the state is changed to talking state 205 by the NEXTSTATE primitive. When the state is changed, the leave signal is generated, and triple 306 is executed whose action definition causes the audible ringing "tone" or "indication" to be removed from handset l05. Since the leave signal is generated internal to ringing state 208, it is not illustrated in FIG. 2; but it is explained in detail with respect to FIG. 38. If customer unit l02 is in ringing state 208 and receives a disconnect signal 222, then triple 307 is executed. This triple indicates the actions performed by customer unit l02 when calling customer unit l03 goes on-hook. However, no connection has been established at this point. If the message is not from the calling customer unit, customer unit l02 simply continues in the ringing state 208. If the disconnect signal 222 was sent by customer unit l03, then the action definition of triple 307 is executed and the NEXTSTATE primitive moves the system back to idle state 20l. If the signal causing the customer unit l02 to leave the ringing state 208 was an off-hook signal 22l, triple 308 causes the answer signal 2l3 to be transmitted to customer unit l03 and causes customer l02 to enter talking state 205. Upon entering talking state 205, triple 320 of FIG. 4 is executed. The latter triple causes the necessary housekeeping to be performed in computer l04 to establish a voice path via bus l00 to customer unit l03. When customer unit l02 goes on-hook, triple 322 is executed causing a disconnect signal 2l9 to be transmitted to customer unit l03 indicating that customer unit l02 has disconnected. In addition, the NEXTSTATE primitive is executed causing customer unit l02 to go to idle state 20l. The execution of the NEXTSTATE primitive generates a leave signal resulting in the execution of triple 32l. The action definition of triple 32l removes the voice connection to bus l00 for customer unit l02 by the execution of the DISENGAGE primitive. In order to explore in greater detail the interscript control mechanism and the activation and deactivation of scripts for controlling a customer unit's environment, consider the scripts illustrated in FIG. 5. The illustrated scripts provide call forwarding (CF script), calling party identification (CPI script), and the activation and deactivation of the call forwarding (CFA script) feature. These scripts are compiled by computer l0l and then downloaded to computer l04 of customer unit l02. Computer l04 illustratively stores these scripts so that when the different events specified within the scripts occur, the CF script has precedence over the CPI and CFA scripts. The call forwarding feature functions by transferring calls intended for customer unit l02 to another customer unit previously identified by the customer entering data via terminal l06. The calling party identification feature displays on terminal l06 which customer unit is attempting to place a call to customer unit l02. For the present example, the call forwarding feature has precedence over the calling party identification. Hence, if the call forwarding feature is active, the calling party identification feature does not display the identification of the calling customer unit since the calling party identification feature is not executed. If call forwarding is not active, then the calling party identification feature identifies all calls that have been placed to customer unit l02 even if the latter is not in the idle state. The CF script for the call forwarding feature consists of triples 50l and 502 as illustrated in FIG. 5 and demonstrates the interscript precedence mechanism using the STOP and CONTINUE primitives. Triple 50l can be executed in any of the states illustrated in FIG. 2. Triple 50l is actuated by an input signal designating that a "#" has been typed on terminal l06. If such an input signal is generated, then triple 50l's event definition sets the $CFNUMBER variable equal to the string of characters that the customer types after "#" on terminal l06. Triple 50l's action definition executes the STOP primitive which results in no further processing of the input signal by any other triples from any scripts in any states. The purpose of executing the STOP primitive here is to stop any further processing of the input signal rather than to control interscript precedence. Assuming that triple 50l has been actuated and that the $CFNUMBER has been set equal to the number for the identified customer unit l03, an origin signal 223 received in any state causes triple 502 to be executed. The execution of triple 502 first results in the $SOURCE variable being set equal to the calling customer unit's number by the event definition. The action definition of triple 502 then checks to determine that the $CFNUMBER variable has been set equal to a nonnull value and that this value is not equal to the calling customer unit's number. If these conditions are true, then the "then" statement of triple 502's action definition is executed resulting in the FORWARD, PRINT, and STOP primitives being executed. The FORWARD primitive transfers the value of the $SOURCE variable to the identified customer unit along with the origin signal 223 indicating that call origination is being attempted. In addition, the PRINT primitive prints a message out on terminal l06 indicating the time at which the call was transferred to the identified customer unit. Finally, the STOP primitive is executed which inhibits the execution of triples in the CPI and POT scripts that respond to the origin signal in the current state of customer unit l02. The execution of the STOP primitive allows the CF script to inhibit the normal operations that would occur upon an attempt being made to set up a call. The STOP primitive is part of the interscript control mechanism. If the conditions defined by the "if" statement of triple 502 are not met, then a CONTINUE primitive is executed. The latter's execution results in control being passed to other triples of lower-precedence scripts. In this case, the origin signal 223 will be handled by the CPI and POT scripts. When the CPI script receives the origin signal 223 in any state, the action definition of triple 504 prints out an indication that a call has been received from the customer unit identified in the origin message and then executes the CONTINUE primitive to invoke the operation of the POT script to set up the call. When control is passed to the POT script, the connection is set up as previously described with respect to FIGS. 3 and 4. Now, consider how the CFA script illustrated in FIG. 5 activates or deactivates the CF script. When the time reaches 8:00 a.m., a time signal is generated, and triple 506 is executed resulting in the CF script being activated if the day of the week is Monday through Friday which are designated as "l" through "5", respectively. At 5:00 p.m., another time signal is generated; and in response, triple 507 is executed and deactivates the CF script if the day of the week is not Saturday or Sunday. Normally, the CF script would have been deactivated on Friday, at 5:00 p.m., if it was Saturday or Sunday. The compiler is executed by computer l0l and is responsive to the scripts illustrated on FIGS. 3, 4, and 5, to compile these scripts prior to the transfer of tne compiled triple code to illustratively computer l04. As is described later, when the compiled scripts are downloaded, the activation operation performed in computer l04 establishes the following precedence among the scripts: CFA, CPI, and CF with the CFA script having the highest precedence. In addition, the CFA, CPI, and CF scripts could be compiled at a latter point in time and downloaded. A program in computer l04 is responsive to the compiled triples of these scripts to store these triples as logically illustrated in FIG. 6 for idle, ringing, and talking states, and to provide a method for executing these triples. The triples associated with the other states would be similarly stored. The triples are grouped by their event definitions for each state. As illustrated in FIGS. ll,l2, and l3, indexing is provided that allows for execution of a triple in response to a signal that corresponds to a particular event definition when the present state corresponds to the state definition. For example, origin signal 223, when received in the idle state 20l, can sequentally activate triple 502 of the CF script, triple 504 of the CPI script, and triple 303 of the POT script. The different processes that are executed in computer l04 to receive the compiled code from computer l0l and to activate, store, and execute this informaton in the logical manner illustrated in FIG. l5, are illustrated in FIG. l0. Also illustrated in the latter figure are the signals communicated between the various processes in the customer units. For example, in the previous discussion, the origin signal 223 transmitted from customer unit l03 to customer unit l02 is received by computer l04 via bus l00 by V_RCV process l002. The latter process then communicates the origin signal 223 to feature control process l000 via an operating system call. The execution of these processes is controlled by an operating system that controls the operation of computer l04. For example, if the customer lifts his or her telephone receiver from its cradle (i.e., goes off-hook), a hardware interrupt occurs causing the operating system to send an interrupt message to V_IN process l002. The latter process responds to the interrupt and determines that the customer has gone off-hook and then transmits the off-hook signal via an operating system call to feature control process l000. The execution of the operating system call to transfer the off-hook signal to feature control process l000 results in the operating system executing feature control process l000. Once feature control l000 is invoked, it first determines what signal it has received, determines the present state of the customer unit, and then executes the triples in that state whose event definition matches the received signal. To illustrate how this matching is accomplished, consider the transmission of an origin message 223 via bus l00 from customer unit l03 to customer unit l02. V_RCV process l00l receives this message and transfers the origin signal to finite state machine (FSM) l005 of feature control l000. FSM l005 is responsive to the origin signal to index into logical signal tables 60l through 606 that are associated with the idle state 20l. FSM l005 then identifies origin logical signal table 602 and has the triples identified by table 602 interpreted by interpreter l006. The manner in which the indexing is performed on actual physical tables, and the identification of the triples to be executed for a given state and signal are detailed with respect to FIGS. ll, l2 and l3. After identifying logical signal table 602, FSM l005 passes a pointer, which is stored in entry CF,502 of table 602, to interpreter l006 to identify the location of the compiled triple code to be executed. The action implemented by the identified triple code is defined by triple 502 as illustrated on FIG. 5. Two different sets of operations can result from the execution of triple 502. The first set results if $CFNUMBER variable contains a number and the calling customer unit is not the customer unit to which customer unit l02 is transferring its calls. If the conditions for the first set of operations are met, then the origin signal and the calling customer unit's number are transferred to the designated call forwarding customer unit by execution of the FORWARD primitive. Also, a notification message is printed on data terminal l06, and the STOP primitive is executed. The effect of the STOP primitive is to cause FSM l005 to cease processing triples in logical signal table 602. The second set of operations is performed when the conditional portion of the "if" statement of triple 502 is false, causing the "else" portion to be executed. The "else" portion of the "if" statement causes the CONTINUE primitive to be executed which results in FSM l005 executing the remaining triples in logical signal table 602. If the CONTINUE primitive is executed, the next triple to be executed in table 602 is triple 504 of FIG. 5 which is pointed to by the CPI,504 entry. The execution of triple 504 results in a message being printed out on terminal l06 identifying the calling customer unit. Next, the CONTINUE primitive is executed which results in the execution of triple 303 as identified by the POT,303 entry in table 602. The execution of triple 303 results in the identification number of the calling customer unit being saved in $ORIGINATOR and $OTHERPARTY and a message being transmitted to the calling customer unit indicating that the called customer unit is entering the ringing state 208. In addition, the NEXTSTATE primitive is executed, resulting in the leave signal being internally generated, the state being changed to the ringing state, and the enter signal being internally generated within feature control l000 by FSM l005. FSM l005 processes the leave and enter signals in a manner similar to the signals being received from another process such as V_RCV process l00l. Further details on the processing of the leave and enter signals is given with respect to FIG. 38 which illustrates the NEXTSTATE primitive. The leave signal relates to the idle state 20l in the present example. Since there are no entries in the logical signal table for the leave signal associated with the idle state, no action results from this signal in the present example. The enter signal which relates to the new state, i.e., ringing state 208, causes the compiled code pointed to by entry POT,305 of logical signal table 6l4 to be executed. This compiled code corresponds to triple 305 illustrated in FIG. 3. The action definition of triple 305 results in the audible ringing tone being applied to handset l05. In addition, the action definition causes the CONTINUE primitive to be executed; however, since there are no more triples to be executed in logical signal table 6l4, no other triples are executed in response to the enter signal. If, during the ringing state 208, handset l05 goes off-hook, this fact is detected by V_IN process l002 and an off-hook signal 22l is transmitted to FSM l005. The latter process identifies that it has received the off-hook signal and that it is in the ringing state and indexes into logical signal table 608. FSM l005 accesses the pointer stored in POT,308 and passes this pointer to interpreter l006 which executes the compiled code for triple 308 as illustrated in FIG. 3. The latter triple transmits the answer signal 2l3 to the calling customer unit by execution of the SEND primitive, and executes the NEXTSTATE primitive to change the state to the talking state 205. The execution of the NEXTSTATE primitive causes the leave signal to be generated for the ringing state and the enter signal to be generated for the talking state. FSM l005 is responsive to the leave signal to direct the interpreter l006 to execute the triple pointed to by entry POT,306 of logical signal table 6l5. The execution of the compiled code for triple 306 illustrated in FIG. 3 results in the ringing tone being removed from handset l05 of FIG. l. In response to the enter signal, FSM l005 indexes into the logical signal tables 62l through 629 associated with the talking state and identifies the triple pointed to by the contents of the POT,320 entry for enter logical signal table 626. This pointer is passed to interpreter l006 which executes triple 320 of FIG. 4. The latter triple causes a voice communication path to be set up between the calling customer unit and customer unt l02 by execution of the ENGAGE primitive. If, during the talking state 205, customer unit l02 goes on-hook, this fact is detected by V_IN l002 process and an on-hook signal is transmitted to FSM l005. The latter is responsive to the on-hook signal to identify and pass the pointer to interpreter l006 contaned in POT,322 of logical signal table 628. The latter pointer points to the compiled code for triple 322 as illustrated in FIG. 4. Execution of this compled code results in the execution of the SEND primitive which transmits the disconnect signal 2l9 to the calling customer unit and the execution of the NEXTSTATE primitive to change the state to idle 20l. The execution of the NEXTSTATE primitive causes a leave signal to be generated for the talking state 205 and an enter signal to be generated for the idle state 20l. FSM l005 is responsive to the leave signal to identify and pass the pointer to interpreter l006 contained in logical signal table 627. The latter pointer points to the compiled code for triple 32l, as illustrated on FIG. 4. Execution of the latter compiled code results in the voice communication path from customer unit l02 to the calling party being broken. Since there is no enter logical signal table associated with the idle state, the generation of the enter signal has no effect. In order to illustrate the effect of the activation and deactivation, consider the following example. Assume customer unit l02 is in the talking state when the real-time clock indicates that it is 5:00 p.m. Tonegen process l004 is responsive to the fact that it is 5:00 p.m. has passed to transmit a time signal to FSM l005. The latter process is responsive to the time signal to identify time logical signal table 625 associated with the talking state. As will be described in greater detail with respect to FIGS. 23 and 24, FSM l005 first passes the pointer pointing to the compiled code of triple 506 to interpreter l006; and after interpreter l006 has finished processing triple 506, FSM l005 passes the pointer from logical signal table 625 for triple 507 to interpreter l006 for execution. The first action of the compiled code for triple 506 is to check whether or not the time is equal to 8:00 a.m., verifying that the event time (8:00) has occurred. Since, in our present example, the time is 5:00 p.m., the event does not match and the action definition of triple 506 is not executed. Interpreter l006 returns control to FSM l005 which then passes the pointer contained in CFA,507 entry of logical signal table 625 that points to triple 507 as illustrated in FIG. 5 to interpreter l006. The latter is responsive to this pointer to start execution of the compiled code for triple 507. The first part of the compiled code for triple 507, as illustrated in FIG. 5, verifies whether or not the event matches the specified time (l7:00) event before proceeding to execute the action definition portion of the triple. Since the time is 5:00 p.m., or l7:00 on a 24-hour time base, and assuming that the day is Monday through Friday, the DEACTIVATE primitive and the PRINT primitive of triple 507 are executed. The DEACTIVATE primitive causes a deactivate signal to be transmitted to FSM l005 indicating that the CF script is to be deactivated. No actual deactivation takes place at this point in time. When FSM l005 receives the deactivate signal, it processes through all of the states to remove all triples that are part of CF script 500, as illustrated on FIG. 5. This process is described in greater detail with respect to FIGS. 23 through 28. In the present example, the CF script 500 does not have a triple whose event definition is responsive to the deactivate signal so the triples can simply be removed by FSM l005, thereby completing the actual deactivation of the CF script. After removal of the triples associated with CF script 500, the logical signal tables of the idle, ringing, and talking states contain the pointers to triples as illustrated in FIG. 7. For example, in the idle state, since the reference to the CF triples has been removed, the calling party identification triple is now the first triple executed in logical signal table 702 when an origin signal is received in the idle state. It would be obvious to one skilled in the art that the inter-feature precedence could be changed by altering the manner in which the references to the triples are stored in the logical signal tables of FIG. 6. For example, to allow the calling party identification to have precedence over the call forwarding, the CPI triples would be placed on top of the call forwarding triples in the logical signal tables. For example, in origin logical signal table 602, the order would be CPI,504; CF,502; and POT,303. Similarly, the entries in origin logical signal table 609 and origin logical signal table 62l would be changed. The PODS script of FIG. 8 illustrates in greater detail, the manner in which a script controls its own deactivation. The latter script is used to provide data service. In addition, the PODS script illustrates the provision of data services for the system illustrated in FIG. l. When the POT, PODS, CPI, CFA, and CF scripts are compiled and downloaded, they are inserted into the logical signal tables such as illustrated in FIG. 6 such that a logical signal table containing a triple for each script would have a CF triple on the top, followed by a CFA triple, a CPI triple, a PODS triple, and finally, a POT triple. When the PODS script is initially activated, triple 80l is executed in response to an activate signal which results in the $DATA and $DEACTIVATE variables being set equal to false. The $DATA variable indicates whether or not a data call is presently in progress; and the $DEACTIVATE variable indicates whether or not the script is to be purged when the idle state is entered. The purpose of a PODS data call is to allow a customer to transmit a message that consists of a plurality of packets from the customer's data terminal to another customer's data terminal. However, it would be obvious to one skilled in the art to extend this script such that the transfer was from a customer unit's computer to another customer unit's computer. Once the customer unit has established the data call to the other customer's data terminal, this data call remains operational until the customer disconnects the data call by inputing the word "disconnect". Consider now, the operation of the PODS script illustrated in FIG. 8 in providing the previously described data call. The customer using, for example, customer unit l02 initially sets up the call by typing a sequence of digits designating the customer unit that is to be called. In response to the entry of digits during the idle state, triple 8l4 is executed resulting in the $DATA variable being set equal to true, and the $ORIGINATOR variable being set equal to the $THIS variable. The SENDMESSAGE primitive is then used to send an origin signal, in the form of a message string, to the party being called, and the NEXTSTATE primitive is utilized to enter the outpulsing state. During the setup of a voice call, the customer would go off-hook in the idle state and would be placed in the dialing state. While in the dialing state for a voice call, the customer would enter a sequence of digits and this would result in only a voice path being set up. Thus, the system distinguishes between a data call and a voice call by the fact that a data call receives the digits designating the called party during the idle state, whereas the voice call receives digits during the dialing state. The called party distinguishes between the origination of a data call and a voice call by the fact that a SENDMESSAGE is utilized to send the "origin" string in a message for a data call whereas the SEND primitive is used to send the origin signal 223 for a voice call. The called party recognizes those facts by the actuation of rcvmessage and origin events. Once in the outpulsing state, customer unit l02 leaves by the occurrence the busy signal, input signal, or the receipt of a ringing message which results in the entry of the idle state, idle state, or audible state, respectively. Triples 8l7 and 8l3 illustrate the action definitions performed upon the occurrence of the busy or input signals, respectively. Triple 3ll, as illustrated in FIG. 3, defines action taken upon receipt of the ringing message signal. When this occurs, the NEXTSTATE primitive is executed moving the customer unit to the audible state. Upon entry into the audible state, triple 8l6 is executed resulting in a message being printed out on terminal l06 indicating that the other party has been alerted. While in the audible state, the customer unit can transfer to the idle state either by the occurrence of the input signal with the string "disconnect", or the occurrence of the busy signal from the called customer unit resulting in the execution of triples 8l2 and 8l7, respectively. When the called customer unit accepts the data call, the latter unit transmits a message to the calling customer unit utilizing the SEND primitive to send an answer message. In response to the event of the answer message being received by the calling unit, triple 3l6 of FIG. 3 is executed resulting in customer unit l02 being transferred to the talking state. Upon entering the talking state, triple 8l0 is executed resulting in a message being printed out that a connection has been made to the identified called customer unit; and since there is a CONTINUE primitive ending the action definition of triple 8l0, control is passed to triple 320 of the POT script as illustrated in FIG. 4. The execution of triple 320 causes a voice path to be set up in addition to the data path between the calling and called customer units. The talking state can be exited by the execution of either triple 8ll or 8l2. Both of these triples transfer the calling customer unit from the talking state to the idle state. The voice path is removed by triple 32l as illustrated in FIG. 4 which is responsive to the leave event in the talking state to execute the DISENGAGE primitive. Consider the establishment of a data call from the point of view of the called customer unit. Upon occurrence of the rcvmessage event having an origin string, triple 806 is executed assuming the called customer unit is in the idle state. Otherwise, triple 805 is executed and a busy signal is sent back to the calling customer unit. The action definition of triple 806 utilizes the SEND primitive to transmit the ringing signal back to the calling customer unit indicating that the called customer unit is entering the ringing state and initializes the $DATA, $ORIGINATOR, $OTHERPARTY variables. Upon entering the ringing state, triple 807 is executed in the called customer unit and a message is printed out on the associated terminal indicating the party who is calling. The state can be changed to the idle state if the calling party terminates the call set-up, indicated by a disconnect signal, which results in the execution of triple 808. The customer at the called customer unit can establish the call by generating an input event with the word "connect" resulting in the execution of triple 809 resulting in the action definition sending an answer signal to the calling customer unit, and changing the state to talking. Upon entering the talking state, triple 8l0 is executed as illustrated in FIG. 9, and in addition, triple 320 as illustrated in FIG. 4 is executed resulting in a voice path as well as a data path being set up. The talking state is terminated at the called customer unit in the same manner as that previously described from the point of view of the calling customer unit. Consider now, in greater detail, the manner in which the PODS script as illustrated in FIG. 8 delays its deactivation after the DEACTIVATE command has been executed from the terminal, such as terminal l06 in FIG. l, specifying that the PODS script is to be deactivated. This delay is to allow the data call to be completed and it is only necessary to delay the deactivation if there is presently a data call in progress. Hence, the state will not be the idle state. Upon the occurrence of the deactivate event and the state not being the idle state, triple 802 is executed resulting in the $DEACTIVATE variable being set equal to true and then the execution of the STOP primitive. As described later with respect to FIGS. 23 and 24, a script indicates to FSM l005 that it will handle its own deactivation by execution of the STOP primitive. Once the data call is completed, and the state is transferred to the idle state, triple 803 is executed. Since the $DEACTIVATE variable is true, the "then" portion of the "if" statement is executed, resulting the PURGE primitive being executed which removes the PODS script from the logical signal tables as illustrated in FIGS. 6 and 7. The data structures utilized by feature control process l000 in identifying which triple is to be executed in response to a given signal are illustrated in FIGS. ll, l2, and l3. The latter figures illustrate a detailed implementation of the logical signal tables represented in FIGS. 6 and 7. When the finite state machine, FSM l005 illustrated in FIG. l0, receives a signal from one of the processes l00l through l004, FSM l005 first utilizes the current state index stored in location ll0l and the state pointer stored in ll02 to determine a location in state table ll04 via path ll03. The value stored at a location in state table ll04 is a pointer that indirectly points to a location in FSMSignal table lll0 via path ll05, FSMSignalPTR location ll07, and path ll08. State table ll04 contains one indirect pointer for each of the possible customer units' states. Similarly, there is one FSMSignalPTR pointer in ll06 through ll07 and ll20 for each of the possible states. Each of the FSMSignal tables ll09 through lll0 and ll2l is associated with one of the possible states. Each entry in an FSMSignal table is associated with an event definition for a signal that can occur in the state associated with that table. For example, once FSM l005 indexes to FSMSignal table lll0, FSM l005 then utilizes the signal number that identifies the signal being processed to index to the correct location within the latter table. The location indexed to in FSMSignal table lll0 points indirectly to ProgramID table lll6 via path llll, triple list lll3, and path lll4. Triple lists such as lll3 are also referred to as FSMSignal locations. For each of the possible signals which any of the states represented by FSMSignal tables ll09 through lll0 and ll2l can respond, there exists for each signal an FSMSignal location lll2 through lll3. ProgramID table lll6 is also illustrated in FIG. l2. A ProgramID table such as lll6 contains references to all of the triples that can respond to the signal that FSM l005 is presently processing and contains references to all the triples contained in the corresponding logical table of FIGS. 6 and 7. In order for FSM l005 to fully process the signal, it is necessary to execute each triple associated with an entry in a table such as ProgramID table lll6 or until the STOP primitive is executed by one of the triples. In order to process all the triples represented by the entries in table lll6, FSM l005 maintains a current index variable and starts to process these entries with the most recently activated triple. Each entry in table lll6 consists of an index into a script table, such as l20l, and an index into a triple table such as l208. Script table l20l is pointed to via path l202 which is an index from the bottom of table l20l pointed to by the SCRIPTS variable. The identified location in script table l20l points to script list l206 via path l203. Before starting to process the information identified in script list l206, FSM l005 stores the pointer identified in script table l20l in the CURRENTSCRIPT variable. Script lists l205 through l207 contain all the information concerning the triples for a particular script that is common to the triples for that script. Within script list l206, as illustrated in FIG. l4, the memory location designated as name l220 contains the name of the script. The location designated as numLiterals l22l contains the number of distinct literals that are used by all the triples in this script. The area designated as literals l222 comprises two segments. The first segment is a table of pointers that are indexed by the literal ID field of a literal argument instruction which designates the actual literal string contained in the second segment of area l222. Ths second segment comprises the literal strings. The area designated numVariables l223 contains the number of distinct variables used by all the triples in the script. The area designated variables l224 comprises the variable names as string variables that are indexed to by the ID field of a variable argument instruction. Variables l224 is used during the initial downloading of the system. Area intToExt l225 is a table of pointers that is indexed by the variable ID field of a variable argument instruction of triple and contains indexes to a global table of variable values. The area designated numTriples l226 defines the total number of triples contained in triple array l208 pointed to by variable l227. Variable id l228 is used to store the index used to index into script array l20l. The variable l229 designates whether the script is currently active or not. Finally, the variable designated deleteScript l230 is used when a script is to be totally removed from memory. Triples l227 in script list l206 of FIG. l2 or FIG. l4 contains a pointer to triple table l208. The latter table contains pointers which indirectly point to the compiled code for the triples of the script. Triple table l208 is indexed into using the triple field from ProgramID table lll6 via path l204. The location indexed by path l204 into triple table l208 points to triple l2l0 that comprises a series of memory locations that, in turn, point to various pieces of information within the actual coded implementation of the triple. There is one coded implementation of a triple for each entry in triple table l208 and a corresponding triple such as triples l209 through l2ll. Once the compiled triple code pointed to by triple l2l0 has been executed, interpreter l006 illustrated in FIG. l0 once again returns control to FSM l005. The latter indexes to the next location in ProgramID table lll6, indexes through a path similar to what was previously described, until the new code for the next triple is identified by one of the triples l209 through l2ll, and then, FSM l005 once again passes control to interpreter l006. This process continues until all of the triples in ProgramID table lll6 have been executed or until one of the triples executes a STOP primitive. The compiled code format of a triple is illustrated in FIG. l5 and is encoded using numerical codes (ASCII). Location l500 defines the number of bytes in the compiled code. The number of states specified in the state definition of the triple (i.e., the number of states to which the triple applies) is stored in location l50l and the numerical IDs of these states are located in location l503. Similarly, the ID of the named event is stored in location l504. There is one compiled triple for each event specified in event definition of the source code triple. The information stored in l50l through l504 is utilized during the activation of a script. The instruction portion or action of the compiled code is contained in locations l505 and l506. Area l505 normally comprises two distinct portions. If there are no event parameters specified in the event definition, then there is just the second portion as described in the following material. The first portion of area l505 is utilized to recover values that are being passed into the compiled triple code by the signal occurrence and to make the determination whether or not the event definition of the triple has been fully satisfied and thus whether or not the subsequent portion should be executed. The second portion of area l505 contains primitives and instructions. Location l506 contains the HALT primitive which causes interpreter l006 to return control to FSM l005 if a STOP or CONTINUE has not been encountered previously in the execution of area l505. The primitives are subroutine calls to C++ functions to perform the actions indicated. The general sequence of the codes in area l505 consists of argument codes followed by instruction codes or a primitive call that use the preceding arguments. The exception to this normal flow of arguments and instructions and primitives is illustrated in FIGS. l7 and l8. FIG. l7 illustrates the assignment instruction where the instruction comes first followed by the internal identification code of the variable to receive the assignment. FIG. l8 illustrates the SENDMESSAGE instruction which can have an optional number of parameters to be transmitted indicated in the second field of the instruction. In general, the argument codes fall into the classes of literals, variables, branch-to-address arguments, or signal arguments. FIGS. l9 and 20 illustrate the format of these instructions for the literal or variable and the signal argument, respectively. When one of these arguments is encountered by interpreter l006, it takes the following internal identification code, labeled as ID, obtains a pointer to the actual value using the ID as an index into a table, and pushes this pointer onto the interpreter stack. When the instruction or primitive using that argument is executed, it pops the stack to obtain the pointer and utilizes this pointer to pass the actual value. Signals are tested and associated values are recovered in the following manner. The event parameters of a triple can transfer information into the compiled triple at the time the triple is executed. This information can consist of a retrieved value for a variable or can consist of a plurality of values, e.g., "input" event. FSM l005 stores any values that must be passed into the event parameter code in the SIGNAL_ARG array. The first instructions of the compiled code for a triple retrieve these values. For an event definition sucn as "origin ($SOURCE)", the value recovery code simply accesses the first location of the SIGNAL_ARG array and obtains the value stored there and sets the $SOURCE variable equal to the retrieved value. In the case of an event such as "input", it is necessary to recover the first input string that was received from the terminal and then to compare this string against the data stored from the compiled triple in a literal table to determine whether or not the input event is exactly matched as it is defined in the triple. If the input event literal information does not match that which has been stored from the complied triple, then control is returned to FSM l005 for execution of the next triple. If the first input string that was received from the terminal matches the first argument of the input event definition, then the remainder of the code of the triple is executed. The rcvmessage, reply, and time events function in a similar manner to that of the input event. In addition, the input, rcvmessage, and reply events also can have a variable number of variable arguments whose values must be obtained from the SIGNAL_ARG array by positional correspondence at the time the triple is executed and stored in the proper variable locations. After the values have been recovered, the remainder of the triple code is executed. The format of a branch instruction is illustrated in FIG. 2l. In the case of a conditional branch, the interpreter pops from the stack the test value which determines a branch or no branch. Tables I, II, and III give the decimal numerical codes for the event, state, and instruction codes, respectively. Event Code origin 0 disconnect 1 off-hook 2 on-hook 3 digits 4 ringing 5 answer 6 busy 7 query 8 idle 9 notidle 10 rcvmessage 11 input 12 reply 13 alarm 14 time 15 activate 16 deactivate 17 enter 18 leave 19 State Code idle 0 ringing 1 talking 2 disconnect 3 dialing 4 busy 5 audible 6 outpulsing 7 Instruction Code Primitives Mnemonic Code HLT 0 ALARM ALM 21 BRU 1 CANCEL CAN 22 BRC 2 APPLY APP 23 LAR 3 REMOVE RMV 24 VAR 4 SEND SND 25 SAR 5 SENDMESSAGE SNM 26 BAR 6 PRINT PRI 27 EQL 7 DIAL DIA 28 NEQ 8 FORWARD FWD 29 GRT 9 ASK ASK 30 LSS 10 ACTIVATE ACT 31 GEQ 11 DEACTIVATE DEA 32 LEQ 12 ASSIGN ASN 33 ADD 13 ENGAGE ENG 34 SUB 14 DISENGAGE DIS 35 MUL 15 NEXTSTATE NXT 36 DIV 16 PURGE PRG 37 NEG 17 CONTINUE CON 38 AND 18 STOP STP 39 ORR 19 NOT 20 FIG. 22 illustrates the manner in which the literal and variable codes of a triple are utilized to gain access to the variable and literal information, respectively. The local variable table 2201, literal table 2204 also called literal 1225 in FIG. 14, and list of literals 2205 are maintained in the associated script list, such as script list 1206 of FIG. 14. List of literals 2205 is part of the compiled script. In the case of a variable, the variable code is utilized to access the local variable table 2201 also called intToExt table, such as 1225, in FIG. 14 from which an index is obtained into the global variable table 2202. The global variable table 2202 is common to all scripts within a given customer unit. From global variable table 2202, a pointer is obtained to the variable values 2203 which contains the actual character string value of the variable. Similarly, the literal code is utilized to access literal table 2204 (1222) from which a pointer is obtained to literal value 2205. All literals and variables in their associated lists are terminated with a null character to designate the end of each respective item of information. During the downloading phase of the system operation, code within the prompt-user process l003 is responsive to data being received from the computer l0l to be stored in the tables illustrated in FIGS. ll, l2 and l3. FIGS. 23 and 24 illustrate in flowchart form, a program for implementing FSM l005. FIGS. 23 and 24 detail the logical flow of the program written in C++ which is described in detail in the book entitled, The C ++ Programming Language , by B. Stroustrup. Once the program illustrated in FIGS. 23, and 24 has been initialized by block 230l, it repetitively executes blocks 2302 through 23l5. Blocks 23l3 and 23l4 perform the deactivation of a script (i.e., the modification of tables and pointers in FIGS. ll, l2, and l3) when a deactivate signal is received, and block 23l5 performs the activation of a script when an activate signal is received. Block 230l first initializes certain variables internal to FSM l005. The $THIS variable is set equal to the calling number of the customer unit and the i_arg variable is set equal to an index into a table of pointers that identify the parameters being passed with different operating system messages. The parameters comprise any string information associated with the signal. When a message is received by FSM l005, the ip pointer is set equal to the location of the next message to be processed from the operating system. As is well known in the art, the operating system can have a plurality of messages awaiting processing by FSM l005 at any point in time and invokes the execution of FSM l005 as long as there are messages to be processed. Block 2303 sets the MSGTYPE variable equal to the message type within the message by utilizing the ip pointer to point to the massage type stored in the area designated by the operating system. Block 2304 utilizes the MSGTYPE index to index into the signal "#" table that contains numerical identification for each signal type. These decimal values are defined in Table IV. Once the numerical code for the signal has been determined in block 2304, decision block 2305 determines whether or not the signal is the activate signal or not. If the signal is the activate signal, then block 2315 is executed. The details of block 2315 are given with respect to FIGS. 29, 30, and 31. Signal Code origin 0 disconnect 1 off-hook 2 on-hook 3 digits 4 ringing 5 answer 6 busy 7 query 8 idle 9 notidle 10 rcvmessage 11 input 12 reply 13 alarm 14 time 15 activate 16 deactivate 17 enter 18 leave 19 Block 2306 is utilized to access into the table FCSIGNALNAME with the SIG variable in order to identify the event corresponding to the present signal being processed and to store the name string for the event in the $EVENT variable. Blocks 2307 and 2308 access the parameters of the operating system message and store these parameters in an array called ARG. Block 2309a implements the paths shown in FIGS. ll and l2 to determine which FSMSIGNAL structure to utilize such as FSMSIGNAL lll3. The latter block implements the logical paths from variables ll0l and ll02 through state table ll04, an FSMSIGNALPTR variable, such as in ll07, and FSMSIGNAL table, such as lll0. Block 2309b sets the current index to zero. The current index is used to index into a ProgramID table such as lll6. In addition, block 2309b sets the return code equal to CONTINUE. During the interpretation of the compiled code, the code for a given triple may change the return code to a STOP. In addition, block 2309a sets the THISSIGNAL variable equal to the SIGNAL variable. Once the entry in an FSMSIGNAL structure, such as lll3, has been accessed, this entry points to a ProgramID table via a triple list, such as in lll3. Blocks 23l0 and 23ll then proceed to execute the compiled code for all of the triples identified in the designated ProgramID table. The designated ProgramID contains pointers which identify for the current state of the customer unit all of the triples that can respond to the signal presently being processed. Block 23lla is utilized to identify a script structure such as l206 of FIG. l2 via the script portion of an entry in the ProgramID table lll6 via a script table such as l20l. The entry in the script table identified as illustrated by path l202 determines the script containing the triple presently being processed. The identified entry in the script table is stored in the CURRENTSCRIPT variable. Block 23llb then identifies the compiled triple code l2l0 to be executed via illustratively the path shown on FIGS. l2 and l3 of path l2l2, path l204, triple table l208, and path l2l5. The variable TP is set equal to the identified triple such as l2l0. Block 23llc then causes the execution of the function "EXECUTE" which actuates interpreter l006 illustrated in greater detail in FIGS. 34, 35, 36, and 37. Block 23llc passes to the interpreter the TP variable which points via the triple l2l0 to the compiled triple code to be executed. The interpreter returns the value of the returned code which is either a STOP or CONTINUE. Block 23lld then increments the current index so that compiled code for the next triple in the designated ProgramID table lll6 can be executed. After block 23ll has been executed, decision block 23l0 passes control to block 23l2 if any of the following conditions are true. First, is the return code equal to STOP. If the return code is equal to a CONTINUE, then block 23ll is reexecuted. However, if the return code is equal to a STOP, then the processing of the current signal ceases and block 23l2 is executed. The second condition that is checked is whether the current index is greater than the number of entries in the designated ProgramID table lll6. The final condition checked is whether or not the triple just interpreted by block 23llc had executed the PURGESCRIPTID routine. Execution of the latter routine would not only have removed the executing triple from the ProgramID table, but possibly other unexecuted triples in the same script. In addition, this final condition is met if initially there are no triples that can respond to the current signal in the current state. If the removal of the unexecuted triples resulted in no other triples left in the designated ProgramID table, then the ProgramID table lll6 is removed and the triple list pointer of lll3 is set to NULL. If any of the three previous conditions are met, block 23l2 is then executed setting the initial conditions for indexing into the ARG table to the correct value for subsequent execution by block 2308. Blocks 23l3 and 23l4 detail the handling of a deactivate signal. The deactivate signal can have a corresponding deactivate event within the script to be deactivated, and a script, by utilizing a deactivate event, can postpone the physical deactivation or purging of the script to a later point in time. This capability is given to scripts whose work cannot be arbitrarily terminated but must go to completion. Such a script is illustrated in FIGS. 8 and 9. A script defers its deactivation to a later point in time by executing a STOP primitive within the script's triple that responds to the deactivate signal. Decision block 23l3 detects execution of the STOP primitive and does not execute block 23l4 which performs the purging of the script. Block 23l4 performs the purging of a script by removing references to all triples contained within the script in all ProgramID tables. Block 23l4 of FIG. 24 is shown in greater detail in FIG. 25. The PURGESCRIPTID procedure functions by cycling through each state and each signal within that state to remove all of the triples associated with the script being deleted from the ProgramID table corresponding to that signal for that state. It utilizes the DELSCRIPT function referenced in block 2505 to remove these triples. The variables i and j are used to index into the states and signals, respectively. Initially, i is set equal to zero by block 250l. All of the states are then checked to see if there are any triples associated with the script being deleted as designated by the contents of the THISSCRIPT argument or parameter. Decision block 2502 determines when all states have been checked by comparing i to the total number of states as contained in the variable FC_STATES. As long as i is less than the total number of states, blocks 2503 through 2507 are executed. For each iteration through blocks 2503 through 2507, block 2503 sets the j variable equal to zero. Decision block 2504 controls the execution of the DELSCRIPT function until all the signals have been deleted. The DELSCRIPT function is passed a pointer identifying the ProgramID table from which it is to delete all triples associated with the script being deactivated. Then DELSCRIPT function then cycles through all of the entries of the designated ProgramID array eliminating the triples associated with the script being deactivated. The i variable is stepping through the state table ll04 of FIG. ll. For each entry in table ll04, an FSM signal table, such as lll0 is identified. The j variable then steps through each entry in the identified FSM signal table with each entry identifying a ProgramID table via a triple list/FSM signal variable such as lll3. The DELSCRIPT function of block 2505 of FIG. 25 is illustrated in greater detail in flowchart form in FIGS. 26, 27, and 28. The triples associated with a script are deleted in two stages. The first stage is for blocks 2604 through 2609 to determine the new number of triples identified in the ProgramID array lll6 which is stored in GOODTRIPLES and the new value for the current index variable which is stored in NEWINDEX. The actual removal of the triples associated with the present script and signal is performed by blocks 26ll through 26l9. The procedure is to create a temporary ProgramID table, transfer all of the triples to be saved from the old table and then make the temporary table the new ProgramID and identify it in a TRIPLELIST variable, such as in lll3. Upon execution of block 260l, the NEWINDEX variable is set equal to the CURRENTINDEX variable. The CURRENTINDEX variable is equal to the index of the triple presently being processed in blocks 23l0 through 23ll of FIG. 24. The variable GOODTRIPLES is initialized to zero. Since blocks 2503 through 2507 of FIG. 25 assume that every signal has a corresponding ProgramID table in each state, it is necessary to verify whether or not the particular signal being processed, indeed, does have a corresponding ProgramID table for a particular state. This determination is performed by decision block 2602. As illustrated in FIG. ll, an FSMSIGNAL table has pointers to a series of triple lists lll2 through lll3. There is one entry for every possible signal in each FSMSIGNAL table and there is a corresponding FSMSIGNAL structure/triple list for each entry. If there is not a triple responsive to a particular signal for a given state, the triple list for that signal contains a null value. If the triple list identified by a particular entry in the present FSMSIGNAL table that the PURGESCRIPTID function is processing contains a null value, then decision block 2602 returns control to the PURGESCRIPT function. If the triple list does not contain a null value, this means that the signal has a set of corresponding triples in this state and control is transferred to block 2603. Consider now, the details of how the determination is made of the number of valid triples that is stored in variable GOODTRIPLES. Decision block 2604 determines whether or not the number of triples identified in the present ProgramID is greater than the maximum number. The maximum number of triples in a ProgramID is stored in location k such as in lll6, as illustrated in FIG. l2. If i is less than the maximum number of triples, then decision block 2605 is executed to determine whether the entry in the ProgramID block is related to the script that is being deleted. If the script index is different than the script presently being processed, which is identified by an entry in the THISSCRIPT variable, block 2609 is executed which increments the GOODTRIPLES variable by one. If the script for the triple entry presently being pointed to by i matches the THISSCRIPT variable, then block 2606 is executed which marks the entry in the ProgramID table pointed to by the i variable as invalid for later processing by blocks 26ll through 26l9. Control is then passed to decision block 2607. The latter decision block determines whether or not the triple that is to be removed is referenced lower in the ProgramID table then the current triple which is being executed and which had actually activated the DELSCRIPT function. If the ProgramID table presently being processed is that of the triple that caused the DELSCRIPT function to be executed and i is less than the current index which points to the triple being executed, then block 2608 is executed which causes the NEWINDEX variable to be decremented by one. This is done since the NEWINDEX variable was set equal to the CURRENTINDEX variable in block 260l. The contents of the NEWINDEX variable are used in block 26l9 to adjust the CURRENTINDEX variable so that execution can continue from the ProgramID table after the present triple has finished being interpreted. Once all the entries in the ProgramID table have been checked for triples that are to be retained, decision block 26l0 is executed to determine if there are any triples left or if all triples in the ProgramID array were associated with the script that is being purged. If the latter condition is true, block 2620 is executed and the triple list is set equal to null value indicating that, for this particular state, there are no triples responsive to this particular signal. Then, the CURRENTINDEX is set equal to zero also so that no attempt is made later to execute another triple from this ProgramID table when control is returned to the FSM l005. If there are triples that were not associated with the script being purged, then blocks 26ll through 26l9 of FIG. 28 are executed. Block 26ll sets a pointer TMPLIST equal to a new table having its number of entries equal to the number contained in the GOODTRIPLES variable. Blocks 26l3 through 26l7 then index through the ProgramID table looking for the entries that are not marked invalid. Any entry that is not marked invalid is transferred to the new array table by blocks 26l5 and 26l6 which insert the script and triple identifications, respectively. After all of the entries in the ProgramID have been checked, control is transferred to 26l8 which sets the triple list pointer from the FSMSIGNAL table equal to the TMPLIST variable. This has the effect of making the new array table into the ProgramID table that is pointed to by the designated FSMSIGNAL table, such as lll3. Block 26l9 then sets the number of triples as stored in the ProgramID table in the k location equal to the number contained in the GOODTRIPLES variable. And sets the CURRENTINDEX equal to the NEWINDEX variable. The operations performed by FSM l005 in response to an activate signal as defined by block 23l5 of FIG. 23 is illustrated in greater detail blocks 2906 through 29ll and blocks 29l7 through 2923 of FIGS. 29, 30, and 3l. Blocks 290l through 2905 illustrate the details of the ACTIVATE primitive. The purpose of blocks 290l through 2905 is to determine the numerical code for the script that is to be activated and then to send an operating system message containing this numerical code as a parameter to process control l000. When process control l000 receives this message, it invokes FSM l005. After FSM l005 has been invoked and determines that the signal is the activate signal, control is transferred from decision block 2305 to block 2906. The latter block initializes i to the script code by obtaining the latter from the list of parameters in the message passed by the operating system. Decision block 2907 determines that the script code is valid; and, if it is, turns over control to decision block 2908. The latter decision blocks determine whether the present script has already been marked as active in the script structure or location such as l206 by first obtaining a pointer from script table l20l through utilizing the variable i as an index into the latter table. Block 2908 then checks the value of the ACTIVE variable l229 of l206. If the present script is marked inactive, then block 2909 is executed. The purpose of the code 2909 through 29ll and blocks 29l7 through 2923 is to insert into the ProgramID tables references to the triples of the script being activated. These references are only inserted into ProgramID tables that correspond to the state and the signal as designated in the state definition and event definition of each triple of the script being activated. As can be seen in FIG. l2, the address of the script table l20l is known and the relationship of the scripts by numerical code can be used to index into table l20l. The information in the latter table is utilized in order to identify the triples of a script by processing, as an example, along path l203, script l206, paths l2l2 and l204, triple table l208, path l2l5, and triple l2l0. Once the triple is identified, then the code shown in block 29l8 can utilize the coded state and signal information within the compiled triple code itself to determine what ProgramID tables must receive a reference to the triple. In block 2909, the THIS pointer is set equal to the contents of the script table l20l indexed by the variable i and is then used to point into the variables for the script l206. The THIS pointer is also used to set the ACTIVE variable, such as l229, to TRUE. The variable t is set equal to one less than the number contained in the NUMTRIPLES variable stored in the script list. The THISSCRIPT variable is set equal to the contents of the variable i. The reason for setting t in this manner is that the first triple of a script has to have the highest priority, hence, it has to be the last triple pushed onto any particular ProgramID table. Pointer TP points to a triple, such as l2l0. As illustrated in FIG. l3, the triple contains pointers that identify the number of states and the signal that the triple associated with the triple list has in its state and event definitions. This information is used by decision blocks 29l7 and 29l9 and in block 29l8, to determine how many states are present in the compiled code. The program illustrated in blocks 29l7 through 2923 takes the compiled code for each triple and inserts references to that code by the utilization of the PUSHTRIPLE function of block 2920 into the ProgramID tables indicated by the coded states and the signal of the compiled triple itself. The variable i is used to index into the states identified in triple's state definition. Further details of this process are given with respect to FIGS. 32 and 33 which illustrates the PUSHTRIPLE function. After all of the states have been processed for a given compiled triple, block 2923 is executed and t is decremented by one, and execution is passed to blocks 29l0 and 29ll. This process results in the triple table, such as l208, being sequentially indexed through and the compiled triples indirectly pointed to by the locations of the triple table being properly identified in the required ProgramID tables. Once all of the entries in the triple table have been processed, decision block 29l0 passes control to block 29l2. Block 29l2 executes code similar to that illustrated by blocks 2306 through 23l4 of FIGS. 23 and 24. This allows the activate signal to be processed by any triples of the recently activated script which contain the activate event. After the activate signal has been processed, i is reinitialized to zero and blocks 29l4 through 29l6 remove all references to triples whose event is "activate" for this particular script from the ProgramID tables by utilization of the DELSCRIPT function that was described with respect to FIGS. 26, 27, and 28. The purpose for eliminating all triples whose event is activate for the present script is so that a later activate signal will not cause these triples to perform any action since the activate event should only occur once for each script. This PUSHTRIPLE function is illustrated in greater detail in FIGS. 32, and 33. When the PUSHTRIPLE function is called, two conditions can exist. The first condition is that the ProgramID table into which the triple is to be placed already exists, and the second condition is that the ProgramID table does not exist. Decision block 320l makes the determination of which condition exists by checking to see if the designated triple list location, such as in lll3, contains a null value indicating that the ProgramID table does not exist. If the ProgramID table does exist, then block 3202 is executed which creates a new array and sets a TMPLIST pointer to identify the location of the new array. Block 3203 is then executed which inserts the script and triple identification into the first entry of the new array, thus, identifying the compiled triple code in this new array. Block 3204 sets up the initial value of the variable i. Blocks 3205 through 3207 copy the script and triple identification information from the original ProgramID table into the new array table. Block 3206 copies the script identification information, and block 3207 copies the triple identification information. Once the contents of the ProgramID table have been completely copied into the new array table, block 3208 is executed which inserts the pointer contained in TMPLIST pointer into the triple list location, such as in lll3, thus making the new array the ProgramID table which is pointed to by an entry in the FSMSIGNAL table, such as lll0. In addition, block 3208 also inserts the number of triples that are identified by the new ProgramID table into the location designated as k in the ProgramID table. FIGS. 34, 35, 36, and 37 illustrate the flowchart for interpreter l006 of FIG. l0. When control is first passed to interpreter l006 from FSM l005, interpreter l006 sets the RETURNCODE variable equal to UNDEFINED and obtains the location of the first instruction to be interpreted by executing block 340l. After performing these initial functions, interpreter l006 continually executes blocks 3402 and 3405 so on through 3434 until a HALT, STOP, or CONTINUE instruction is encountered. Once a HALT, STOP, or CONTINUE instruction is encountered, RETURNCODE is set to STOP or CONTINUE (the latter for both HALT and CONTINUE instructions) blocks 3403 and 3404 are executed and control is returned to FSM l005 along with the RETURNCODE value. As previously noted, the HALT, STOP, or CONTINUE instructions terminate the execution of the coded instructions by resetting the RETURNCODE variable and cause control to be returned to FSM l005 of FIG. l0. If RETURNCODE remains equal to UNDEFINED, decision block 3405 is executed to determine whether an unconditional branch instruction is the next instruction to be executed. If the unconditional branch instruction is present, the interpreter stack is popped, and the popped value is stored into the PC variable resulting in the interpreter branching to a new position in the code determined by the popped value. The popped address was originally put on the stack by a branch argument instruction being detected by decision block 34l7. Then block 34l8 obtains the jump index as was illustrated in FIG. 2l, and adds this index to the location of the first instruction address of the code and pushes the result onto the stack. The execution of a conditional branch instruction is shown in blocks 3406 through 34l0. Before the execution of a conditional branch, a branch argument instruction would have been executed placing onto the stack an index to where the branch is to occur. Once a conditional branch instruction is detected by decision block 3406, control is transferred to block 3407 which stores the popped branch address index into a local variable designated as "P". Next, decision block 3408 pops from the stack the address of the TEMP variable which contains the result of a comparison and/or a logical operation that had been placed on the stack by execution of a compare instruction and/or a logical operator instruction as illustrated by blocks 34l9 and 3420 and 3425, 3426, 3427, and 3428. If the result of the compare and/or logical operation was true (nonzero), block 3409 is executed causing the branch to occur to the designated place in the code in a manner similar to that performed by block 3438. If the result of the compare and/or logical operation instruction was false (zero), then block 34l0 is executed and the next instruction of the compiled code is executed. If a literal argument instruction is encountered, decision block 34ll transfers control to block 34l2. The latter block first obtains the literal ID field from the instruction whose format is illustrated in FIG. l9. The literal ID is utilized to access a literal table containing pointers to a list of literal strings both of which are contained in the script list, such as script list l206 of FIG. l2. Once the pointer is obtained, it is pushed onto the interpreter stack. Similarly, if a variable argument instruction is encountered, decision block 34l3 transfers control to block 34l4. Block 34l4 functions similarly to 34l2 with the exception that the ID field is utilized to index into a local variable table to obtain a pointer to the global variable table. The latter pointer into the global variable table is pushed onto the stack by block 34l4. Also, blocks 34l5 and 34l6 function similarly to blocks 34ll and 34l2 in obtaining a pointer to the signal argument from a list of signal arguments maintained on a global basis. Blocks 34l9 and 3420 function to implement the various compare operations by first popping the two values to be compared from the stack and then storing the result of this comparison into a temporary variable. A pointer to this temporary variable is then pushed onto the stack by block 3420. Functions are provided for comparisons based on equal, not equal, greater than, less than, greater than/equal, and less than/equal. Note, that the interpreter may use a number of temporary variables which are freed when the interpreter executes block 3403. Similarly, blocks 342l and 3422 function to perform the arithmetic operations of addition, subtraction, multiplication, and division. Blocks 3423 and 3424 function similarly to the arithmetic instructions except that the unary negation function is performed on only one variable. Also, a logical opcode instruction as illustrated by blocks 3425 and 3426 is handled in a manner similar to that of the arithmetic instructions by blocks 342l and 3422. Similarly, the NOT instruction is handled in a manner similar to the NEGATE instruction and is illustrated in blocks 3427 and 3428. The execution of primitives, such as SEND, is illustrated by blocks 3429 and 3430. Once a primitive is detected, then the operations shown in block 3430 are performed. Most of the primitives have either no parameters or a fixed number of parameters. Pointers to these parameters have been placed onto the stack by earlier argument instructions and are simply popped off of the stack and passed to the primitive function. However, two types of primitive instructions, ASSIGN and SENDMESSAGE, have a different format. An ASSIGN primitive format is illustrated in FIG. l7. When the ASSIGN instruction is encountered, block 3430 accesses the second field of the instruction to obtain the ID of the variable in the compiled code to set that variable equal to the top value on the stack. The SENDMESSAGE format is illustrated in FIG. l8. First the SENDMESSAGE instruction is encountered and then block 3430 accesses the second field of the instruction illustrated in FIG. l8 to obtain the number of optional parameters to be passed in addition to the two parameters always implied by this instruction. Block 3430 uses this number of optional parameters to determine how many additional arguments to pop from the stack. The HALT and CONTINUE primitives are implemented by blocks 343l and 3432. Once the HALT or CONTINUE is detected, control is passed to block 3432 which sets the RETURNCODE equal to CONTINUE. Similarly, when the STOP instruction is detected by decision block 3433, control is passed to 3434 which sets the RETURNCODE equal to stop. The NEXTSTATE primitive is illustrated in greater detail in flowchart form, in FIG. 38. Upon invoking the NEXTSTATE primitive, block 380l first verifies that the state is being modified and, if it is, block 3802 is executed. The latter block sets the $EVENT variable equal to the string "leave" and executes code similar to that illustrated in blocks 2309 through 23l2 of FIGS. 23 and 24. This results in the leave signal being processed in the normal manner. After this has been accomplished, block 3803 is executed to change the $STATE variable equal to the string representation for the numerical state code contained in the newState argument and to change the CURRENT variable ll0l to index the entry for the new state in state table ll04. Finally, block 3804 is executed which causes the $EVENT variable to be set equal to the string "enter" and code similar to that illustrated in blocks 2309 through 23l2 of FIGS. 23 and 24 is executed resulting in the enter signal being processed for the new state. It would be obvious to one skilled in the art to have the functions performed by computer l0l performed by each customer unit's computer for that customer unit using known software techniques. In addition, it would be further obvious to have all functions performed by the computers illustrated in FIG. l performed by one computer using known software techniques.

Claims: A method for controlling state transitions in response to a plurality of signals in a voice and data telecommunication system having a plurality of system states and with control being performed by a computer executing a program written in a nonprocedural language and said program controlling said system to provide a plurality of features each providing specific voice and data operations and each feature implemented by a set of groups of instructions including a first, a second and a third group of instructions with each group of instructions being actuated by a predefined one of said signals and said system being in a predefined one of said system states, comprising the steps of: initiating a change from the present one of said system states to another one of said system states by the execution of an instruction of said first group of instructions; generating a leave signal to define preparation to exit from said present one of said states; performing common exit operations terminating said present one of said system states before leaving said present one of said system states by the execution of said second group of instructions in response to said leave signal and said system being in said present one of said states; generating an enter signal to define preparation to enter into said other one of said states; and performing common entrance operations to start said other one of said system states upon entering said other one of said system states by said third group of instructions actuated by said enter signal and said system being in said other one of said system states. The method of claim 1 wherein each of said group of instructions comprises an event definition defining the actuating signal and a state definition defining the actuating one of said system states and wherein occurrence of the defined signal in the defined state causes the actuation of said group of instructions and each of said group of instructions is identifiable by the defining actuating signal and the defined one of said system states and wherein said step of performing said common exit operations comprises the steps of: finding said second group of instructions on the basis of said leave signal and said present state; and executing said common exit operations by the execution of instructions from said second group of instructions. The method of claim 2 wherein said step of executing said common exit operations further comprises the steps of: finding a fourth group of instructions responsive to said leave signal and said present one of said system states upon execution of instructions from said second group of instructions; and executing additional common exit operations to terminate said present one of said states by the execution of instructions from said fourth group of instructions. The method of claim 3 wherein said step of executing additional instructions comprises the step of stopping execution of other groups of instructions being actuated by said leave signal and said system being in said present one of said system states by execution of one instruction of said fourth group of instructions. The method of claim 2 wherein said step of performing the common entrance operations comprises the steps of: finding said third group of instructions on the basis of the enter signal and said other one of said system states; and executing said common entrance operations by instructions of said third group of instructions. The method of claim 5 wherein said step of executing said common entrance operations further comprises the steps of: finding a fifth group of instructions responsive to said enter signal and said other one of said system states upon execution of an instruction from said third group of instructions; and executing additional common entry operations to start said other one of said system states by execution of instructions from said fifth group of instructions. The method of claim 6 wherein said step of executing said additional common entrance operations further comprises the step of stopping execution of other groups of instructions responsive to said enter signal and said system being in said other one of said system states. A voice and data telecommunication system controlled by a computer in response to a plurality of signals from said system, said system having a plurality of states, said computer executing a program comprising a finite state machine routine and sets of groups of instructions with each set of said groups of instructions providing a feature on said system and each group of instruction being actuated by a predefined one of said signals and said system being in a predefined one of said system states, comprising: means for initiating a change from the present one of said system states to another one of said system states; means for generating a leave signal to define preparation to exit from said present one of said system states; means for performing common exit operations to terminate said present one of said system states before leaving said present one of said system states in response to said leave signal and said system being in said present one of said system states; means for generating an enter signal to define preparation to enter said other one of said system states; and means for performing common entrance operations to start said other one of said system states upon entering into said other one of said states in response to said enter signal and said system being in said other one of said system states. The system of claim 8 wherein said means for performing said common exit operation comprises means for continuing the processing of said leave signal; and means responsive to the continued processing of said signal for performing additional common exit operations to define preparation exit from said present one of said system states. The system of claim 9 wherein said performing means further comprises means for terminating further processing of said leave signal thereby inhibiting other means actuated by said leave signal and said present state. The system of claim 10 wherein said means for performing said common entrance operation further comprises means for continuing the processing of said enter signal; means responsive to the continued processing of said enter signal for finding another means responsive to said enter signal and said other state; and said other means responsive to said enter signal and said other one of said system states for performing additional common entry operations to start said other one of said system states. The system of claim 11 wherein said means for performing additional common entrance operations comprises means for terminating further processing of said enter signal thereby blocking execution of other means actuated by said enter signal and said system being in said other one of said system states.

Inventors: HANSEN, TERRIS LEE, HYATT, WAYNE EDWARD, LEUNG, WU-HON FRANCIS, MONTGOMERY, WARREN ALAN
Applicants: AMERICAN TELEPHONE AND TELEGRAPH COMPANY
Application year: 1986
Main classification: G06F9
IPC codes: H04Q3, G06F9