Preface

ThisspecialissueoftheJournalofComputerScienceandTechnologycontainsthePro-ceedingsoftheinternationalSummerSchoolandWorkshoponFormalModelsofProgram-mingandtheirApplications,heldinBeijingonSeptember17-20,1997.ThiseventwaspartoftheKIT(KeepinTouch)ProjectSYMSEMoftheEuropeanUnion,andwasjointlyorganizedwithLaboratoryofComputerScience,InstituteofSoftware.'KeepinTouch'isaprogrammeaimedatmaintainingandenhancingthelinksbetweennon-EuropeanscientistsandEuropeaninstitutions.Thepartnersofthissp…     

A functional analysis of the network: A prerequisite for deregulating the telecommunications industry

Due to the obvious inefficiency of regulatory authorities, the introduction of potential competition in the markets of natural monopolies has recently been emphasized in theoretical publications. In spite of its limitations the framework of contestable markets has been the analytical background of decisions in various industries. The purpose of this paper is to discuss the application of these theories to the telecommunications network as a whole. Econometric models have failed to establish that the telecommunications cost function is subadditive, mainly because networks are heterogeneous from an economic point of view: information is transmitted with increasing returns to scale, while there are growing economies of scope between the data processing industry and the handling, by digital switching equipment, of the calls’ content and of the signalling and addressing information. To allow for this current technical evolution the deregulation process should dissociate the transmission network, which is a natural monopoly, and the traffic routing networks, which could be gradually opened to a limited competition. In this new structure there would be a wholesale market in which a regulated monopoly would rent transmission facilities (leased circuits, dedicated access loops, …) and a competitive retail market in which operators would sell traffic and value added networks to residence and business customers.     

Influence de la tarification horaire sur le trafic téléphonique

As the evening peakload of trunk traffic became higher than the morning one, a new time-of-day pricing was initiated in France on June 1985. The effects of this tariff change on the traffic profile and the telephone revenues were previously estimated, using an econometric model, fitted from traffic observations provided by similar experiments carried out in Germany and Switzerland. This model, based on probabilistic choice theory, uses the Logit formulation adapted to the case of a continuous set of options (times-of-day), and provides simulations of traffic trade-offs due to changes in the time-of-day pricing. Data collected since June 1984 enable us to measure the actual effects of the new tariffication. Compared with the model forecasts, these observations show a good fitting for the 6 p.m. to 8.30 p.m. period (the 8 p.m. peak-load decrease is consistent with the forecast); in the late evening however, traffic is higher than expected. These new data allowed us to improve the formulation and the fitting of the model; these recent developments are presented here.     

Le service universel quelle valeur? quel coût? quel financement?

The opening up to competition of public utilities, such as telecommunications, raises the issue of maintaining and financing the universal service obligation, previously ensured by a monopoly. In this paper, a simple model deals with a welfare and cost analysis of the universal service. It compares two valuations of the private cost, i.e. the reduction of the operator profit: the avoidable cost and the budgetary compensation. Under the assumptions of the model, the budgetary compensation is higher than the avoidable cost. The paper scrutinizes different competitive situations. If an entrant can skim up the profitable users without a better technology, the final situation is economically inefficient as a result of the splitting of infrastructure, even though the incumbent gets a compensation. When a technological advantage makes entry desirable, network duplication can be avoided through interconnection and access charges. In order to cover the deficit of the universal service operator, an universal service fund has to be set up in addition to access charges.     

l’analyse du fonctionnement interactif à l’évaluation du marché des téléconférences

The authors are concerned with the comparative analysis of interactive processes in a meeting, subject to various situations of mediation. The research is based on the analysis of records of actual meetings, either in face to face situations, or in audio or video-conferences. Interactivity is first defined as the ability to interrupt in order to help the communication process. The mechanisms which regulate this interactivity are then analyzed, as well as its functions in the way exchanges proceed and speech is built. The thesis is put forward that parallel to the exchange of informations linked to the contents of the meeting, an exchange of control signals, chiefly of an infra and non verbal kind, takes place as on a signalling channel, the role of which is to regulate: the allocation of speech turn-taking, the mutual understanding of participants, the setting out of the speech issued on the main channel, the construction of the common knowledge useful to the achievement of the task, the regulation of speech status, the production of ambiguous and unopposable speeches… The study enables identification of the disturbances brought to the regulation of interactivity when the technical conditions of mediation do change, and allows improvement of the designing of the protocoles aimed at selecting voice and image data before their transmission through teleconferencing systems.     

Allosteric activation of Arabidopsis threonine synthase by S-adenosylmethionine

Plant threonine synthase, in contrast to its bacterial counterpart, is strongly stimulated by S-adenosylmethionine via a noncovalent interaction [Giovanelli et al. (1984) Plant. Physiol. 76, 285-292]. The mechanism of activation remained, however, largely unknown. To further characterize this unusual role for S-adenosylmethionine, the Arabidopsis thaliana threonine synthase was overexpressed in Escherichia coli, purified to homogeneity, and then used for kinetic and enzyme-bound pyridoxal 5'-phosphate fluorescence equilibrium-binding experiments. We observed that the activating effect of S-adenosylmethionine results from an 8-fold increase in the rate of catalysis and from a 25-fold decrease in the Km value for the O-phosphohomoserine substrate. The data can be well fitted by a kinetic model assuming binding of two S-adenosylmethionine molecules on the native enzyme. We suggest that the dramatic modifications of the enzyme kinetic properties originate most presumably from an allosteric and cooperative transition induced by S-adenosylmethionine. This transition occurs at a much faster rate in the presence of the substrate than in its absence.     

Tarification,discrimination et contournement

This paper illustrates on an example the optimal (nonlinear) pricing policy by a monopolistic operator of a local telecommunications network facing competition in the market for access to long distance carriers (bypass). We start by providing a brief overview of the literature on non-linear pricing and on bypass. As a benchmark, we consider a monopoly facing no threat of competition and having access to two distinct technologies: the network technology and the bypass technology, which is more efficient for reaching large individual customers. We then study competition between bypassors and the original network operator. We characterize the optimal tariff, analyze the resulting allocation and provide comparative statics.     

Sequential algorithms on concrete data structures

We provide a sequential denotational semantics for sequential programming languages, based on a new notion of sequential algorithm on the Kahn-Plotkin concrete data structures. Intuitively an algorithm may be seen either as a concrete object—a “program” in a simple output-driven language — or as an abstract object — the pair of a sequential function and of a computation strategy for it. The concrete and abstract presentations are equivalent, as shown by a representation theorem. The algorithms form a cartesian closed category with straightforward solutions to recursive domain equations. Hence they may replace functions in the denotational semantics of any sequential language. An applicative programming language based on sequential algorithms is presented in a companion paper.