Broadband Communication Networks Research Articles

Computational costs of fast stochastic simulation techniques for Markovian fluid models in multiservice networks

Two accelerated simulation techniques, Importance Sampling and RESTART, are analyzed in the context of the class of Markovian fluid models, widely used in broadband communication networks. The different terms corresponding to their computational cost are exposed and evaluated for a sample case. Importance Sampling is found to be preferable (i.e. to present the lower computational cost) for the simulation of very rare events and large systems. A tentative criterion is proposed for the a priori selection of the computationally lighter simulation technique, based on the system size and on the probability of the event being estimated.

The SALADIN project

It is apparent that, in the near future, software production will be more and more involved with applications running on heterogeneous networks, often with mobile components. Witness the increasing availability of reliable broadband communication networks, which span local, metropolitan and worldwide areas, and the high popularity of newly conceived applications on Internet, such as the World Wide Web. The development of applications for heterogeneous distributed networks that support mobile components (in short, programming mobile agents) demands innovative design and programming techniques. In this report we summarize the activities and results achieved in the SALADIN project, an Italian National project funded by the Italian Ministry of University and Research. We consider our experience interesting for the Software Engineering community because it has been a successful experiment in putting together teams whose expertise was sensibly different and complementary. This has allowed us to exploit the cooperation of different complementary competencies that are needed to reach significant results in an area where methods and tools, which are specific of several area of computing come naturally together.

Effective bandwidth estimation and testing for Markov sources

This work addresses the resource sharing problem in broadband communication networks that can guarantee some quality of service (QoS), and develops some results about data source and traffic modelling, especially in aspects of model testing and parameter estimation. The multiplexing of variable bit rate (VBR) sources poses a mathematical and statistical problem: the estimation of the resource requirements of a source or set of sources. The estimation method shall be simple enough to be practically implemented in the connection acceptance control (CAC) function. In this paper, the VBR video sources are taken as a typical case of variable rate, with real-time constraints. This association of requirements makes the case especially interesting. A Markov model is assumed for the VBR sources. The validity of such models is under research; they seem to be appropriate at least in certain time scales. The model is tested against real video traces. In order to estimate the resource allocation or “channel occupation” of each source, the concept of equivalent bandwidth proposed by Kelly [Notes on effective bandwidth, in: F.P. Kelly, S. Zachary, I.B. Ziedins (Eds.), Stochastic Networks: Theory and Applications, Oxford University Press, Oxford, 1996, pp. 141] is used; it is based on a consistent mathematical theory, and has proven to be robust and useful for technical applications. A calculation of the equivalent bandwidth of a Markov source, given its parameters, can be found in the literature [IEEE ACM Trans. Networking 1 (4) (1993) 424]. But in fact, one can only estimate model and parameters. In this work, an estimation of the equivalent bandwidth is given, which can be obtained from real data. The convergence and the consistency of the estimation are studied, and practical bounds are found. Illustrative calculations are performed from real video traces that were obtained using a software MPEG coder, developed by the authors. The mathematical and statistical results are valid for whatever phenomenon that can be modelled as a Markov process.

BROADBAND NETWORKS FOR DISTANCE EDUCATION AND TRAINING: SOME RESULTS AND PRACTICAL SOLUTIONS FROM A HUMAN FACTORS INVESTIGATION

Distance education and training is one of the most promising application fields of broadband networks. The present contribution is focused on one of the main opportunities provided by broadband communication networks for distance education: advanced and interactive virtual classroom situations. In particular a virtual classroom field experiment, which employs broadband cellular radio telecommunication technologies is described. The investigation was realised, in cooperation, by Fondazione Ugo Bordoni (FUB) and RAI (Italian Public TV), using the tools made available by the human factors discipline. Some results of the investigation are presented concerning learners' performance and usability of the multimedia tele-education system including factors such as: ease of use usefulness; telepresence efficiency; users' satisfaction. Furthermore, operational results and practical solution coming out of the experiment are shown as well. They include the basic features of multimedia systems used in virtual classroom and the correct procedures for training teachers and learners in the equipment use.

Measurement-Based Usage Charges in Communications Networks

We study usage-sensitive charging schemes for broadband communications networks. We argue that a connection's “effective bandwidth” is a good proxy for the quantity of network resource that the connection consumes and can be the basis for a usage charge. The determination of effective bandwidth can be problematic, however, since it involves the moment-generating function of the cell arrival process, which may be difficult to model or measure. This article describes methods of computing usage charges from simple measurements and relating these to bounds on the effective bandwidth. Thus we show that charging for usage on the basis of effective bandwidths can be approximated well by charges based on simple measurements.

Testing VBR video traffic for stationarity

It has been previously reported that variable bit rate video traffic displays signs of long-range dependence (Beran et al. 1995, and Garrett 1993), which is defined within the framework of weak stationarity. The concept of weak stationarity is of fundamental practical interest, because it implies the existence and independence with time of mean and autocovariance. Since mean and variance might be used as parameters for policing the traffic stream on a broadband communication network, it is important to verify the underlying assumption of weak stationarity. The results presented in this paper strongly call into question this assumption. As a possible explanation, we offer shifting level processes which are asymptotically weakly stationary for infinite sample sizes.

Some approaches to solving a multihour broadband network capacity design problem with single-path routing

In this paper, we consider solution approaches to a multihour combined capacity design and routing problem which arises in the design of dynamically reconfigurable broadband communication networks that uses the virtual path concept. We present a comparative evaluation of four approaches, namely: a genetic algorithm, a Lagrangian relaxation based subgradient optimization method, a generalized proximal point algorithm with subgradient optimization, and, finally, a hybrid approach where the subgradient based method is combined with a genetic algorithm. Our computational experience on a set of test problems of varying network sizes services) shows that the hybrid approach often is the desirable choice in obtaining the minimum cost network while the genetic algorithm based approach has the most difficulty in solving large scale problems.

Scheduling support for multicasting sessions in broadband communication networks

Multimedia applications require support from the underlying broadband network at the end-to-end communication level. Multicasting is an important paradigm of end-to-end communication. The root node of a multicasting session is responsible for controlling the session including monitoring, maintenance, and the implementation of the multicasting protocol. The job that controls the multicasting session executes as a group of tasks at the root node of a multicasting tree. The scheduling scheme at the root node should give support to a multicasting session by improving the completion time of the jobs controlling the multicasting session, hence increasing throughput and the probability of admitting new multicast sessions into the system. In this paper, we model the tasks that carry out the multicasting session monitoring and maintenance as a fork-join job executing on a multiprocessor system. We assume that an executing task blocks for device I/O as a part of the activities associated with sending and receiving data packets. We develop two analytic models for scheduling a session control job on a multiprocessor system. The first model allows incoming job tasks to multiplex processors with existing tasks of another multicasting session, while the other model schedules a task of the incoming job to an idle processor. We assume that the overhead of rescheduling a task to another processor is large. We compare the performance of both models and show the range of conditions under which a model outperforms the other. We point out how the results can be used in the design of an adaptive scheduler that uses both models to improve throughput and consequently the probability of admitting new multicast sessions.

Routing in broadband communication networks using neural computations

This paper will briefly review some of the published work on applying Artificial Neural Networks (ANN) to routing in Asynchronous Transfer Mode (ATM) networks and critically appraise some of the conclusions which have been drawn from these studies. The paper will go on to explain the design and implementation of a simulation of a neural network array superimposed on a simulated ATM network. The results of routing experiments, which were compared with decisions made using Shortest Path First (SPF) routing, will be discussed and the need for appropriate comparison metrics explained. The paper will end with a review of what needs to be considered when the applicability of ANNs to ATM network control is being assessed and the required functionality of simulation tools which allow these assessments to be made.

A Tabu Search algorithm for the optimisation of telecommunication networks

A Tabu Search (TS) algorithm is presented for topological optimisation of broad band communication networks whose structure is based on a single exchange and on a number of multiplexing centres. Considering the high cost of the fiber optic cable, the network architecture is a minimum spanning tree. The optimisation problem is reduced to choose the number and the locations of the multiplexing centres. This leads to model the network by a binary string in which ones and zeroes indicate activation or non-activation of multiplexing centres in the nodes. A TS algorithm has been implemented using a dynamically changing tabu-tenure, a frequency based long term memory structure and an aspiration criterion. Extensive testing over networks of various sizes and configurations is made in order to choose the best values of the parameters. The performances of the algorithm are compared to those of other more traditional techniques

A control-theoretic approach to adapting VBR compressed video for transport over a CBR communications channel

Future broad-band communications networks are expected to be dominated by video and image traffic. Variable bit-rate (VBR) video compression is generally preferred to constant bit-rate (CBR) compression because constant image quality can be provided. In contrast, CBR transport is preferred to VBR transport from the networking standpoint because of its simplicity. This paper studies the important issue of adapting VBR compressed video for transport over a CBR channel. We focus on temporal traffic smoothing using an elastic buffer. The target image quality and the output rate of the video encoder is controlled by feedback based on the buffer-occupancy level. Previous adaptation schemes are not readily analyzable. An analyzable control-theoretic adaptation framework is proposed. It allows systematic and quantitative investigation of issues such as stability, robustness against scene changes, robustness against image-quality oscillations due to coding-mode switching, and tradeoffs between image-quality and buffer-occupancy (delay) fluctuations. Perhaps more importantly, the framework opens up many new possibilities for further research.

Long-tail buffer-content distributions in broadband networks

We identify conditions under which relatively large buffers will be required in broadband communication networks. For this purpose, we analyze an infinite-capacity stochastic fluid model with a general stationary environment process (without the usual independence or Markov assumptions). With that level of generality, we are unable to establish asymptotic results, but by a very simple argument we are able to obtain a revealing lower bound on the steady-state buffer-content tail probability. The bounding argument shows that the steady-state buffer content will have a long-tail distribution when the sojourn time in a set of states with positive net input rate itself has a long-tail distribution. If a set of independent sources, each with a general stationary environment process, produces a positive net flow when all are in high-activity states, and if each of these sources has a high-activity sojourn-time distribution with a long tail, then the steady-state buffer-content distribution will have a long tail, but possibly one that decays faster than the tail for any single component source. The full buffer-content distribution can be derived in the special case of a two-state fluid model with general high- and low-activity-time distributions, assuming that successive high- and low-activity times come from independent sequences of i.i.d. random variables. In that case the buffer-content distribution will have a long tail when the high-activity-time distribution has a long tail. We illustrate by giving numerical examples of the two-state model based on numerical transform inversion.

Next-generation multiservice VSAT networks

Very-small-aperture terminal (VSAT) satellite networks have so far been successful in the provision of specific communication services to geographically dispersed users. However, user demands are becoming more complex and VSAT networks are expected to provide a much wider range of services (voice, data and multimedia). This paper investigates how this service integration could be achieved and shows that performance improvements are possible if efficient multi-access protocols and speech compression with voice-activity-detection techniques are used. It also discusses the future role that VSATs could play in the provision of access to the integrated broadband communication network to remote users. It is shown that it could be possible to use VSATs for ATM service provision, but there are limitations on the system's performance from the satellite delay and limited link capacity.

A FLEXIBLE POLYMER FIBRE INFRASTRUCTURE FOR AN EVOLUTIONARY CUSTOMER PREMISES NETWORK

The developments in compressed digital video technology are paving the way for video-based services. Provision of such services requires a broadband communications network, which should extend into the customers' premises up to the terminals. This indicates a growing need for a customer premises network. This paper presents an infrastructure for an evolutionary and future-proof customer premises network. Such an infrastructure allows for early deployment and gradual upgrades associated with service demand. A key element in the concept is the use of the graded index polymer optical fibre (GIPOF) which combines an intrinsically high bandwidth with easy and therefore low-cost handling. There are two opposite approaches for the choice of network topology. In one approach, all applications are forced onto a single topology. In the other approach, the topology best suited for each application type is used. This paper considers the ‘best-suited topology’ approach and presents a network infrastructure that can support many topologies simultaneously as independent overlay networks. The proposed infrastructure consists of bundles of fibres, which can be interconnected and accessed by terminals in any required manner.

An IN-Based Multimedia The VoD Approach to theDesign of Interactive Services Over Broadband Networks: The VoD Example

The evolving Interactive Multimedia (IMM) services require the development of flexible and easily adaptable design tools that can interoperate with the underlying broadband communication network. In this paper, we adopt a design philosophy based on the Intelligent Network (IN) concept. The main advantage of this approach is the transparency of the service-specific features to the underlying signaling system. Hence, a fast introduction of demanding services becomes possible even if the signaling of the network is not sophisticated enough to fully cover the requirements of IMM services. The standard International TelecommunicationUnion (ITU) Service Independent Block (SIB)-based methodology is used as a basis and further extended, where necessary, to cover new requirements, not originally predicted for Narrowband-Integrated Services Digital Network (N-ISDN), but arising from IMM services. The paper further proceeds with the development of an Interactive Multimedia Object Class Library (IMOCL) which adopts a high-level object-oriented approach that supports an easy evolution of IN-based service design towards implementation. The IMOCL is kept generic to the most possible extent aiming to provide a common framework for the design of a wide variety of IMM services using the IN concept. The IMOCL encompasses service management functionality enabling the designer and provider of an IN service to manage the newly introduced service. Both ITU SIB-based and IMOCL methodologies, together with the standard Specification and Description Language (SDL) technique are demonstrated in the design of selected parts of a typical Video on Demand (VoD) service.

DIALECT—Network-based digital interactive lectures

In the information society of today the access to information is a fundamental right and a strong demand for cost effective just-in-time distance learning can be observed. The newest technical achievements in the fields of telematics and multimedia offer new ways for the design and distribution of learning material. Different approaches have already been tested successfully. The degree of involvement of a human expert during the learning process with computer based material is still under investigation. The work presented in this paper deals with the problem of converting university lectures into multimedia based digital learning material (learnware). The courses called Digital Interactive Lectures (DIALECT) require minimal interaction with the teacher and can be distributed over a broadband communication network. In order to increase the acceptance of DIALECT material a new model based on an integrated concept has been developed. It eliminates many of the weaknesses of traditional CBT courses and modern Open Distance Learning. Basically a “realistic story” that illustrates the theory to be presented and the accompanying case study (exercise) is developed and integrated into the lecture. This is accomplished with the help of interactive video which is used to present the topic, to guide through the parts of the lecture and to catch the students' attention. DIALECT makes use of animation, computer simulation, and hyperlink facilities. The authors' interface is based on the notion of hyperlinked scripts and enables the inclusion of the appropriate media where needed. A corresponding framework for programmers that allows for easy and efficient use of multimedia-based presentation tools has been developed. Special attention has been paid to the user front-end in terms of screen design, interactivity and good video/audio quality. The lectures are stored in compressed format on a UNIX server and can be presented on low-cost multimedia Windows PCs. Real time distribution over a digital network requires Quality of Service features because of the demand for constant bit transfer rate for the videos. DIALECT applications are well suited for ATM networks or high speed LANs. First evaluation results show a high degree of acceptance. Will high quality multimedia lectures in some years compete with inferior-performing teachers?

The Old and the New

In 1993 for the Venice Biennale, Nam June Paik initially proposed to title his exhibition in the German Pavilion Electronic Super Highway: “Bill Clinton stole my idea!” His brash claim comes from a 1974 document commissioned by the Rockefeller Foundation, in which Paik proposed connecting Los Angeles and New York with “multi-layer to broadband communications networks, such as domestic satellites, wave guides, bunches of co-axial cables, and fiber-optics. The expenses would be as high as the moon landing, but the ripple effect ‘harvest’ of byproducts would be numerous.”

Photonic access concentrator for ATM gigabit switching fabrics

In future broadband communication networks the interest for purely photonic switches is due to the bandwidth mismatch between optical transmission networks and electronic switching nodes. Photonic ATM switching fabrics mainly based on wavelength-switching stages are therefore being studied, to implement high capacity switches with also concentration, multiplexing and demultiplexing functions, using state-of-the-art photonic technology. The architecture of an ATM photonic access concentrator is described in this paper, illustrating the design and implementation of its basic subsystems, the traffic concentrator and the cell multiplexer. The design guidelines are outlined in detail referring to an example, where 128 user lines at 622 Mb/s are given access to 4 outlets at 2.488 Gb/s. The corresponding implementation, based on the systematic use of cell wavelength encoding, makes use either of well-known photonic components, such as Fabry-Perot filters, fiber delay lines, splitters and combiners, either of recently developed devices, like high-speed optical gates and tunable filters and lasers. Finally, the system feasibility is demonstrated presenting the results obtained on a reduced size and speed experimental setup of the cell multiplexer.

Satellites in UMTS and B-ISDN: status of activities and perspectives

Satellites are no longer seen as an alternative to a terrestrial mobile telecommunications system or the (optical-fibre-based) integrated broadband communications network. Instead they are now being considered as one of the components of the Universal Mobile Telecommunications System being developed within the European Union's RACE Programme for the next century and as a component of the broadband ISDN. This paper discusses the role played by satellites in these systems and the issues which have to be addressed. >

The ACOSTA accompanying measure A2106

At a time when the informatics and telecommunications industries are looking for new markets to exploit in relation, for example, to the emerging ISDN and broadband communications networks, there is a need to create a broad consensus in Europe by bringing together systematically the relevant industries including telecom service providers, health care providers, insurance organisations, standardisation experts and policy makers. The aim of the ACOSTA (Consensus Formation and Standardisation Promotion) Accompanying Measure is the creation of more general awareness of the relevant environment among all the parties, better specification of common requirements and options taking better account of the real needs of the users, and enlargement of the common market in health care telematics.