The onset of the 6G era in telecommunications, touted to launch in 2030, is hoped to serve many masters and deliver an unparalleled improvement in capabilities, applications, intelligence, and indeed liberate human potential. The vision of 6G incorporates new radio frequencies and technologies, the integration of sensing, cognitive methods defining both network functions and their management, and new networking approaches for a broader scope of applications and distribution. The challenges for inventors lies in both physical devices and a substantive improvement in the development of functions implemented by, and managed, with software. The algorithms (including dynamic solutions based on Artificial Intelligence and Machine Learning), protocols, and architecture evolutions will bring together the most advanced software systems ever imagined for telecommunications. Yet, the business of companies building and operating these next generation platforms requires a huge investment, and 6G will exceed all others with its breadth and complexity. This paper outlines one possible timeline of technological impact based on the pace of invention, investment, global context, and the broad goals of 6G. From this, follows a vision of the critical methods in automation, security and networking that we believe will be central to bringing the dream of 6G to a reality.

User and system behaviour is difficult to predict for novel systems, and this affects the capacity of the system (the number of active users that can be supported with acceptable response delay). This leads to a range of values, in the form of a feasible or acceptable region for the potential capacity, conditional on the uncertain parameters. This work considers uncertainties in the delay between requests (user think time), network latency, and cache behaviour due to users' locality of reference. The acceptable region is shown to be bounded approximately by linear constraints which are easy to derive. This simple result is useful for sensitivity and scalability analysis, and appears to have been overlooked. It is applied to a Web-based system for telephony, using voiceXML for service ranging from interactive voice response, to voice-based E-mail.

Telepresence is the application of computing and telecommunications to support a sense of social proximity among distant collaborators. These applications use a variety of multimedia communications and presentation techniques to achieve these goals. Paramount in these applications is the need to provide distributed control, and to some extent distributed information exchange. A network services interface (NSI) has been developed to provide the control and data exchange backplane for telepresence applications. Two case studies illustrate its use: a re-implementation of the Xerox Portholes concept that shows the ability of NSI to support existing applications by simple means; and an implementation of a generic conference control system and its instantiation to manage multiple conference rooms.>

A timeline is a linear, graphical visualization of events over time. For example, in concurrent application, events would represent state changes for some system object (such as a task or variable). A timeline display generator creates the graphical visualization from some record of events. This paper reports on a model for timeline display generators based on a formal model of event history and the objectives of timeline visualization. In this model, any timeline display generator is completely described through the definition of a set of mathematical functions. The exact characteristics and flexibility of a particular implementation of a timeline display generator, depends on the way in which these functions have been implemented. The current prototype, xtg, (Timeline Display Generator for X-windows) serves as an example implementation of these ideas. Characteristics of xtg are presented, and its use in the analysis of a real-world client-server application is discussed. Xtg has been applied to several other applications to-date and is being applied by several telecommunications companies to areas ranging from software process analysis to call trace data analysis.

This paper presents the Entity Behavior Description (EBD) modelling technique for specifying the behavioral requirements of a set of communicating entities in a concurrent system. EBDs are finite state machines which describe the abstract behaviour of an entity. This abstract behavior is defined as the combination of the application-specific behavior, and the semantics of the communications. EBDs are given formal operational semantics which explicitly separate these two behavioral components; and, as such, are a fundamental component of a design process which emphasizes the strong traceability of behavioral requirements in a design.>

NRC publication: Yes

Review of: Bertsekas, D. P., and Tsitsiklis (1989) Parallel and Distributed Computation: Numerical Methods, Prentice-Hall, Englewood Cliffs, NJ. Reviewed by: Harvey J. Greenberg. Review of: Van Hentenryck, Pascal (1989) Constraint Satisfaction in Logic Programming, MIT Press, Cambridge, MA. Reviewed by: John W. Chinneck and Gerald M. Karam. INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.

A temporal logic-based specification language and deadlock analyzer for Ada is described. The deadlock analyzer is intended for use within Timebench, a concurrent system-design environment with support for Ada. The specification language, COL, uses linear-time temporal logic to provide a formal basis for axiomatic reasoning. The deadlock analysis tool uses the reasoning power of COL to demonstrate that Ada designs specified in COL are systemwide deadlock-free: in essence, it uses a specialized theorem prover to deduce the absence of deadlock. The deadlock algorithm is shown to be decidable for finite systems and acceptable otherwise. It is also shown to have a worst-case computational complexity that is exponential with the number of tasks. The analyzer has been implemented in Prolog. Numerous examples are evaluated using the analyzer, including readers and writers, gas station, five dining philosophers, and a layered communications system. The results indicate that analysis time is reasonable for moderate designs in spite of the worst-case complexity of the algorithm.>

The programming tradeoffs between structure-oriented and clause-oriented operations on data structures in Prolog are limited in current implementations because the assertion of clauses that include uninstantiated variables destroys any binding between these variables and those with which they are unified in the execution of the program. Built-in predicates for Prolog that allow one to assert predicate variables pointers, which are constants, rather than uninstantiated variables, are presented. The author shows: the possible performance benefits of clause-oriented implementations of data structures over equivalent structure-oriented versions, the logical implications of the proposed built-in predicates, and their practical significance by integrating them in C-Prolog and evaluating the two different implementations of the symbol table dictionary in D.H.D. Warren's pseudo-Pascal compiler example.>

The commenter disagrees with the comparison method used and questions the usefulness of the results obtained in the above named work by N.R. Howes and A.C. Weaver (see ibid., vol.15, no.12, p.1507-17, 1989). It is claimed that the comparison method is weak because Howes and Weaver did not take into account: the impact of control flow within a protocol, the coordination required between multiple entities executing within a layer and which share the services of a lower layer, and optimizations of R.J.A. Buhr's architecture (1984) which would have improved its performance efficiency.>

Starvation and critical race analysis tools for Ada designs are described. These tools are part of a temporal analysis toolset that includes an operational specification language, a language interpreter, and a deadlock analyzer for Ada. The starvation analyzer is based on a set-theoretic model of starvation. It uses a proof tree produced by the deadlock analyzer to define the possible computation space of the design. A preprocessing phase of the starvation tool optimizes the analysis so that the resulting analysis is efficient. Unlike livelock analysis in state machines, the starvation analyzer does not require a priori specification of home states to discern liveness. The critical race analysis tool provides semiautomatic proof of critical races by identifying nondeterministic rendezvous (races) from the proof tree generated by the deadlock analyzer, and then assisting the human operator in identifying which of these constitute critical races. Several design examples are used to demonstrate the capabilities of the two analysis methods.>

A research project is described in which an experimental software CAD environment called the Carleton embedded system design environment (CAEDE), oriented toward embedded systems and Ada, was developed to provide a demonstration of the concept and to serve as a research testbed. The major contribution of CAEDE is a demonstration of a visual paradigm which combines semantic depth and syntactic shallowness, relative to Ada, in a manner that makes it possible for the embedded-system designer to work in terms of abstract machines while still thinking Ada. A secondary contribution is the identification of Prolog as a promising approach for supporting tool development in an environment which supports the visual paradigm. Also described are experimental tools for temporal analysis, performance analysis, and the generation of skeleton Ada code.>

It is noted that critical races in concurrent Ada programs are an insidious source of system errors, and that the Ada language does not have concurrency features to ease the development of critical race-free programs. The authors illustrate this using the CRF language, which extends the Ada language by the addition of a powerful caller selection mechanism. It is this facility that implements a discriminatory mutual exclusion (dimutex) construct, an important feature for building less critical race-prone programs. The MLog language supports the CRF caller selection mechanisms; thus it is convenient as a rapid-prototyping platform. A design method for systematically converting CRF designs into Ada designs is presented. The method uses a mixture of mechanical and creative transformations that are guaranteed not to introduce critical races. D. Helmbold and D. Luckham's (1985) gas-station example is used to illustrate the various approaches to applying the design method.>

This paper presents an approach to high-level support of office workers by embedding office knowledge in a network of distributed cooperating knowledge-based or expert “assistants” and servers. These knowledge-based systems incorporate both factual and procedural knowledge and are capable of making use of existing conventional office technology. They constitute a form of computer-supported cooperative work. We describe a common architecture for our assistants and servers that incorporates several key features. Our systems are capable of supporting concurrent multiple consultations or tasks and have facilities for the interruption and resumption of consultations as appropriate. The various assistants and servers, which may reside on different machines, cooperate in solving problems or completing tasks by passing messages. We propose a taxonomy of the general office knowledge normally used by office workers, together with a frame and rule-based knowledge representation scheme. We also describe an experimental system, written in PROLOG, that incorporates the above design principles.

This paper reports upon the design of an expert system at the Canada Centre for Remote Sensing for updating maps of forested areas using Landsat imagery. The system is decomposed into a number of specialist experts organized in a hierarchical fashion around a series of blackboards which are used for communications between the different levels. At the lowest level in the hierarchy, is an expert which acts as the interface to the low-level, procedural-based, image processing algorithms. A short review of expert systems, with special emphasis on the analysis of remotely sensed imagery, is first given. Various approaches to treating uncertainty in expert systems are then discussed, in particular, the approach based upon the theory of evidence. The forestry map updating problem is described and the classical solution presented. Our hierarchically organized expert system is then presented in the context of this problem. Finally, an expert interface to the image processing algorithms is described.