Telephone Switching Systems Research Articles

Artificial Intelligence on the Move: A Revolutionary Technology

People have used technology to improve themselves throughout the human history. From the ancient times, human beings tried to get their work done by human slaves or inanimate machines. To build intelligent agents each new technology has been exploited. Clockwise, hydraulics, telephone switching systems, holograms, analog computers and digital computers have all been suggested both as mechanisms for intelligent agent and as technological metaphors for intelligence. A new invention of computer system is known as Artificial Intelligence that can perform tasks with the help of human intelligence. Artificial Intelligence associated with computer systems which includes various types of intelligence: systems that understand new concepts and tasks, systems that are able to give reason and draw useful conclusion about the world around us, systems which can learn a natural language and comprehend a visual scene. Artificial Intelligence means intelligence that is demonstrated by machines. This is a device that recognizes its environment and takes action that increases the chances of achieving its goal. The research goal of Artificial Intelligence is to create technology which helps computers and machines to perform various tasks in an intelligent manner. Artificial Intelligence analysis the intelligent acts of computational agents. Computational agent is one whose decisions about his/her actions can be explained in terms of computation. His actions, firstly, may be broken down into primary operation that further can be applied in a physical device. Computations have many forms, for example: In humans, it is in the form of “wetware” and in computers it is in the form of “hardware”. Greatest advances have occurred in the field of game playing. Super computer named Deep Blue defeated world chess champion Gary Kasparov in May, 1997. This research article explains history, features and goals of artificial intelligence. It also explains various types of artificial intelligence like reactive machine,limited memory, theory of mind and self- awareness. This article focus on application of artificial intelligence in many fields like literacy, finance, heavy industries, hospitals, news, publishing, transportations, telecommunication maintenance, telephone and online customer services etc.

A Visual Formalism for Interacting Systems

Interacting systems are increasingly common. Many examples pervade our everyday lives: automobiles, aircraft, defense systems, telephone switching systems, financial systems, national governments, and so on. Closer to computer science, embedded systems and Systems of Systems are further examples of interacting systems. Common to all of these is that some "whole" is made up of constituent parts, and these parts interact with each other. By design, these interactions are intentional, but it is the unintended interactions that are problematic. The Systems of Systems literature uses the terms "constituent systems" and "constituents" to refer to systems that interact with each other. That practice is followed here. This paper presents a visual formalism, Swim Lane Event-Driven Petri Nets, that is proposed as a basis for Model-Based Testing (MBT) of interacting systems. In the absence of available tools, this model can only support the offline form of Model-Based Testing.

Seamless Implementation of a Telephone Switching System Based on Formal Specifications in RTPA

The Telephone Switching Systems (TSS) is a typical real-time system that is highly complicated in design and implementation. In order to deal with the extreme complexity in real-world settings, a suitable and efficient mathematical means is required beyond any programming language. To this purpose, an efficient and precise denotational mathematics known as the Real-Time Process Algebra (RTPA) and the RTPA methodology for system modeling are introduced. Empirical experimental results are reported in this paper on the implementation of TSS based on formal models of the system in RTPA. Three phases of experiments are designed on TSS conceptual modeling, system interface design, and programming implementation and testing. All groups in the experiments with 7 to 8 members have been able to efficiently understood, design, and implement the TSS system in a simplified version in four weeks, which has been estimated as a 10+ person-year project in the industry. The efficiency and expressiveness of RTPA are empirically demonstrated base on the case studies in the experiments.

The Formal Design Model of a Telephone Switching System (TSS)

A typical real-time system, the Telephone Switching System (TSS), is a highly complicated system in design and implementation. This paper presents the formal design, specification, and modeling of the TSS system using a denotational mathematics known as Real-Time Process Algebra (RTPA). The conceptual model of the TSS system is introduced as the initial requirements for the system. Then, the architectural model of the TSS system is created using the RTPA architectural modeling methodologies and refined by a set of Unified Data Models (UDMs). The static behaviors of the TSS system are specified and refined by a set of Unified Process Models (UPMs) such as call processing and support processes. The dynamic behaviors of the TSS system are specified and refined by process priority allocation, process deployment, and process dispatching models. Based on the formal design models of the TSS system, code can be automatically generated using the RTPA Code Generator (RTPA-CG), or be seamlessly transformed into programs by programmers. The formal model of TSS may not only serve as a formal design paradigm of real-time software systems, but also a test bench of the expressive power and modeling capability of exiting formal methods in software engineering.

A scalable method for testing real-time systems

Real-time systems (RTSs) are used in different domains such as telephone switching systems, air traffic control systems and patient monitoring systems. The behavior of RTSs is time-sensitive; that is, RTSs interact with their environment with input and output events under time constraints. The violation of such time constraints is the main cause of the misbehavior of RTSs, and may result in severe damage to human lives and the environment [Mandrioli, D., Morasca, S., & Morzenti, A. 1995. ACM Transactions on Computer Systems, 13(4), 365---398]. To prevent failures in RTSs, we must verify that the implementation of an RTS is correct before its deployment. Testing is one of the formal techniques that can be used to achieve this goal. It consists of three main phases: test generation, test execution, and test results analysis. This paper presents a test case generation method for RTSs modeled as Timed Input Output Automata (TIOA). The approach is made in two steps. First, the TIOA describing the system being tested is sampled to construct a subautomaton, which is easily testable (i.e., easy to generate test cases from it). Then, the resulting subautomaton is traversed to generate test cases. Our method is scalable in the sense that it generates a small number of test cases even when the specifications are significant. Moreover, the test cases derived by our method are executable (i.e., they can be run on any error-free implementation of the system being tested).

A framework for dynamic software architecture-based self-healing

Self-healing is an active topic in areas like large complex distributed systems and continuous running systems, such as telephone switching systems, banking systems, mobile embedded systems. The architecture-based self-healing approach uses the architectural model as a basis for system reconfiguration. In architecture-based self-healing systems, the architectures may also be changed. The architectures that changes during system running are dynamic software architectures. In this paper, an approach of self-healing system based on dynamic software architecture is proposed. To make the system architecture observable and controllable, architectural reflection is used. Meanwhile, architectural style is used to ensure the consistency and correctness of the changes.

The Styx® architecture for distributed systems

A distributed system is constructed from a set of relatively independent components that form a unified but geographically and functionally diverse entity. Examples include networked operating systems, Internet services, the national telephone switching system, and, in general, all the technology using today's diverse digital networks. Nevertheless, distributed systems remain difficult to design, build, and maintain, primarily due to the lack of a clean, perspicuous interconnection model for the components. Our experience with two distributed operating systems, Plan 9® and Inferno®, encourages us to propose such a model. These systems depend on, advocate, and generally push to the limit a fruitful idea — to present their resources as files in a hierarchical name space. The objects appearing as files may represent stored data, but they may also be devices, dynamic information sources, interfaces to services, and control points. The approach unifies and provides basic naming, structuring, and access control mechanisms for all system resources. A simple underlying network protocol, Styx®, forms the core of the architecture by presenting a common language for communication within the system. Even within nondistributed systems, the presentation of services as files advantageously extends a familiar scheme for naming, classifying, and connecting to system resources. More important, the approach provides a natural way to build distributed systems by using well-known technology for attaching remote file systems. If resources are represented as files and there are remote file systems, one has a distributed system — resources available in one place are usable from another.

Performance Analysis of Retrial Queueing Systems Using Generalized Stochastic Petri Nets

We consider retrial queueing systems, in which an arriving customer finding the server busy, may repeat his call after a random duration. The consideration of repeated calls introduces great analytical difficulties. In fact, detailed analytical results exist for some special retrial queueing systems, while for many others, the performance evaluation is limited to numerical algorithms, approximation methods and simulation. Retrial queues have been widely used to model many problems in telephone switching systems, telecommunication and computer networks. In this paper, we show a method of modelling and analysing retrial queueing systems, using the Generalized Stochastic Petri nets (GSPNs).

The Real-Time Process Algebra (RTPA)

The real-time process algebra (RTPA) is a set of new mathematical notations for formally describing system architectures, and static and dynamic behaviors. It is recognized that the specification of software behaviors is a three-dimensional problem known as: (i) mathematical operations, (ii) event/process timing, and (iii) memory manipulations. Conventional formal methods in software engineering were designed to describe the 1-D (type (i)) or 2-D (types (i) and (iii)) static behaviors of software systems via logic, set and type theories. However, they are inadequate to address the 3-D problems in real-time systems. A new notation system that is capable to describe and specify the 3-D real-time behaviors, the i>real-time process algebra (RTPA), is developed in this paper to meet the fundamental requirements in software engineering. RTPA is designed as a coherent software engineering notation system and a formal engineering method for addressing the 3-D problems in software system specification, refinement, and implementation, particularly for real-time and embedded systems. In this paper, the RTPA meta-processes, algebraic relations, system architectural notations, and a set of fundamental primary and abstract data types are described. On the basis of the RTPA notations, a system specification method and a refinement scheme of RTPA are developed. Then, a case study on a telephone switching system is provided, which demonstrates the expressive power of RTPA on formal specification of both software system architectures and behaviors. RTPA elicits and models 32 algebraic notations, which are the common core of existing formal methods and modern programming languages. The extremely small set of formal notations has been proven sufficient for modeling and specifying real-time systems, their architecture, and static/dynamic behaviors in real-world software engineering environment.

Telephone switching systems [Book Review

Telephone switching systems [Book Review

Reliability Analysis of the Retrial Queue with Server Breakdowns and Repairs

Retrial queues have been widely used to model many problems arising in telephone switching systems, telecommunication networks, computer networks and computer systems, etc. It is of basic importanc...

Does code decay? Assessing the evidence from change management data

A central feature of the evolution of large software systems is that change-which is necessary to add new functionality, accommodate new hardware, and repair faults-becomes increasingly difficult over time. We approach this phenomenon, which we term code decay, scientifically and statistically. We define code decay and propose a number of measurements (code decay indices) on software and on the organizations that produce it, that serve as symptoms, risk factors, and predictors of decay. Using an unusually rich data set (the fifteen-plus year change history of the millions of lines of software for a telephone switching system), we find mixed, but on the whole persuasive, statistical evidence of code decay, which is corroborated by developers of the code. Suggestive indications that perfective maintenance can retard code decay are also discussed.

Adventures in the Forth Dimension

Forth is a language that, for most programmers, is like the back side of the Moon: they know it is there but have never laid eyes on it. Yet Forth is mature (about as old as Lisp or C); ubiquitous in everyday applications such as automated tellers, package tracking, airline reservations, telephone switching systems, and microcontrollers everywhere; and built into millions of personal computers and workstations in the guise of IEEE Open Firmware. The page description language PostScript also has its roots in Forth.

Performance evaluation of telecommunication systems with forcible cutoff control scheme

The rapid growth of computer-communication services means that telephone-conversation traffic must compete for system resources with computer-communication traffic carried by dial-up connections to the Internet or intranets over public telephone switching networks. The traffic characteristics differ for the two types of service; for example, the mean holding time and peak traffic periods are different. However, because dial-up connection calls occupy circuit lines for a long time, the grade of service (GoS) of telephone-conversation calls may deteriorate during periods of peak demand. Another problem is that since a telephone switching network is dimensioned to satisfy the required GoS for telephone calls during peak demand periods, there will be surplus resources, and a significant opportunity cost, during off-peak periods. One way to efficiently use these surplus switching-network resources is to offer fixed-cost best-effort dial-up connection service during off-peak periods for telephone traffic. This also makes the demand for dial-up connections less likely to affect the GoS of telephone-conversation calls during peak periods. We propose a priority control scheme for such an off-peak service. This scheme works as follows in a telephone switching system where both high-priority telephone-conversation calls and low-priority dial-up connection calls are offered. When a call arrives at the system and there are adequate resources available for an ordinary telephone-conversation call, a high-priority telephone call or a low-priority dial-up connection call can be connected. However, if a high-priority call arrives at the system and there are not enough resources available to allow connection, an already connected dial-up connection call is forcibly cut off to enable connection of the high-priority telephone call, and thus guarantee the GoS of telephone calls. We evaluate the performance of a telecommunication system based on this scheme by using a Markov model. We derive the call-blocking probabilities for both call types and the ratio of the amount of traffic that is forcibly cut off to the amount of offered traffic in the system, and show calculated results. We also discuss some guidelines for offering services using this scheme. © 2000 Scripta Technica, Electron Comm Jpn Pt 1, 83(6): 78–87, 2000

Configuring large systems using generative constraint satisfaction

The authors used generative constraint satisfaction as the basis for Lava, an automated configuration they developed for the complex domain of telephone switching systems. They built Lava using Cocos, their knowledge-based configuration tool.

Lessons from the design of a PC-based private branch exchange

We designed TigerSwitch, a digital private branch exchange (PBX) implemented on an IBM PC-compatible platform, as an experiment in embedded system design. A telephone switching system is an interesting example of embedded system co-design because it combines a rich functionality with deadlines ranging from seconds to tenths of a millisecond. This paper uses design decisions from TigerSwitch to illustrate the difficulties faced in the partitioning and allocation of a system specification into an architecture: the critical performance paths may not be obvious from the initial specification, and it is often difficult to obtain the performance data required to allocate functions in the architecture.

Using partial-order methods in the formal validation of industrial concurrent programs

Formal validation is a powerful technique for automatically checking that a collection of communicating processes is free from concurrency-related errors. Although validation tools invariably find subtle errors that were missed during thorough simulation and testing, the brute-force search they perform can result in excessive memory usage and extremely long running times. Recently, a number of researchers have been investigating techniques known as partial-order methods that can significantly reduce the computational resources needed for formal validation by avoiding redundant exploration of execution scenarios. This paper investigates the behavior of partial-order methods in an industrial setting. We describe the design of a partial-order algorithm or a formal validation tool that has been used on several projects that are developing software for the Lucent Technologies 5ESS/sup (R/) telephone switching system. We demonstrate the effectiveness of the algorithm by presenting the results of experiments with actual industrial examples drawn from a variety of 5ESS application domains.

A framework for evaluating specification methods for reactive systems-experience report

Numerous formal specification methods for reactive systems have been proposed in the literature. Because the significant differences between the methods are hard to determine, choosing the best method for a particular application can be difficult. We have applied several different methods, including Modechart, VFSM, ESTEREL, Basic LOTOS, Z, SDL, and C, to an application problem encountered in the design of software for AT&T's 5ESS telephone switching system. We have developed a set of criteria for evaluating and comparing the different specification methods. We argue that the evaluation of a method must take into account not only academic concerns, but also the maturity of the method, its compatibility with the existing software development process and system execution environment, and its suitability for the chosen application domain.

Using partial-order methods in the formal validation of industrial concurrent programs

We have developed a formal validation tool that has been used on several projects that are developing software for AT&T's 5ESS ™ telephone switching system. The tool uses Holzmann's supertrace algorithm to check for errors such as deadlock and livelock in networks of communicating processes. The validator invariably finds subtle errors that were missed during thorough simulation and testing; however, the brute-force search it performs can result in extremely long running times, which can be frustrating to users. Recently, a number of researchers have been investigating techniques known as partial-order methods that can significantly reduce the running time of formal validation by avoiding redundant exploration of execution scenarios. In this paper, we describe the design of a partial-order algorithm for our validation tool and discuss its effectiveness. We show that a careful compile-time static analysis of process communication behavior yields information that can be used during validation to dramatically improve its performance. We demonstrate the effectiveness of our partial-order algorithm by presenting the results of experiments with actual industrial examples drawn from a variety of 5ESS ™ application domains, including call processing, signalling, and switch maintenance.

Measured performance of a special-purpose database engine for distributed system software

Open distributed systems include general service functions that set special requirements for information storage. We have developed a special-purpose database engine to meet these requirements. In this paper we describe our database engine and its measured performance. The database engine is memory based, relational, and supports properties that enable it to be used as an object based system. We justify the feasibility of our approach by a numerical example involving a telephone switching system. The example shows that the measured database engine performance is of the correct magnitude for the needs of demanding distributed systems.