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

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

Yingxu Wang (University of Calgary, Canada) and Yousheng Tian (University of Calgary, Canada)
DOI: 10.4018/jssci.2012040105
OnDemand PDF Download:
$30.00
List Price: $37.50

Abstract

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.
Article Preview

1. Introduction

A Telephone Switching System (TSS) is a complex real-time system (Thompson, 2000; McDermid, 1991; Wang, 2007, 2009). The functional structure of the TSS system can be described by a conceptual model as illustrated in Figure 1, which consists of four subsystems known as the call processing, subscribers, routes, and signaling subsystems.

Figure 1.

Functional structure of the TSS system

In the conceptual model of the TSS system, its configuration encompasses 1 call processor and 16 subscribers. There are 5 internal switching routes and a set of 5 signaling trunks providing the dial, busy, ringing, ring-back, and special tones. The call processor modeled by a set of functional processes operates on the line scanners, call records, digits receivers, signaling trunks, system clock, and routes in order to implement a coherent program-controlled switching system.

An important finding in the basic research in software engineering is that any software system, including the hybrid hardware and software system can be rigorously modeled by a set of structural models, a set of process models, and their interactions (Hoare, 1978; Wang, 2002, 2007; Wang & King, 2000). The structure model (SM) is a rigorous abstraction and formal representation of the system’s architecture and components. The process model (PM) is a rigorous description of the system’s behaviors and operations onto the abstract SMs.

  • Definition 1. An abstract Structure Model (SM) is a generic architectural model for a software system, its internal control structures, and its interfaces with hardware components and external input/output, which can be rigorously modeled and refined as an n-tuple, i.e.:

    (1)

where Si, 1 ≤ in, is a set and also a type of elements e that share the property pi.
  • Definition 2. An abstract Process Model (PM) of a program ℘ is a composition of a finite set of m embedded processes according to the time-, event-, and interrupt-based process dispatching rules,, i.e.:

    (2)

where si and sj are one of the 17 RTPA meta-processes, rij is one of the 17 RTPA algebraic process operations, and ek is a general, timing, or interrupt event.

This paper reports an empirical experiment on the implementation of the TSS system based on formal models of the system in RTPA for conceptual modeling, system interface design, and programming implementation. In the remainder of this paper, the architectural designs of TSS in term of the structure models (SMs) in both RTPA and UML are described in Section 2. The functional designs of TSS in term of the process models (PMs) in both RTPA and UML are elaborated in Section 3. A set of comparative experiments in the design and implementation of the TSS system by three groups is demonstrated in Section 4.

2. The Architectural Design Of Tss Based On The Formal Models In Rtpa

As described in Definition 1, the structure model is a rigorous abstraction and formal representation of the architecture of a system and the layout of a component. This section formally describes the structure models of TSS at the hierarchical levels of system and components from the top down, before the process models of TSS can be rigorously elaborated in Section 3.

Complete Article List

Search this Journal:
Reset
Open Access Articles: Forthcoming
Volume 9: 4 Issues (2017): 3 Released, 1 Forthcoming
Volume 8: 4 Issues (2016)
Volume 7: 4 Issues (2015)
Volume 6: 4 Issues (2014)
Volume 5: 4 Issues (2013)
Volume 4: 4 Issues (2012)
Volume 3: 4 Issues (2011)
Volume 2: 4 Issues (2010)
Volume 1: 4 Issues (2009)
View Complete Journal Contents Listing