Miltiades E. Anagnostou

Performance Analysis of the Selective Repeat ARQ Protocol

Delay, queue length, and throughput are the main performance characteristics of a data transmission system with ARQ (automaticrepeat-request) error control. Various protocols which have been proposed use, as a part or as a whole, the basic selective-repeat ARQ protocol. Their performance analysis has, however, been restricted to the throughput characteristics. An easily applicable method to analyze this basic protocol has not appeared in the literature so far. In this paper, two different methods for the queue length and delay analysis are presented. The system is modeled as a discrete time queue with infinite buffer storage. Transmission errors are considered to be independent, and block arrivals may follow an arbitrary interarrival time distribution. The first method uses an exact Markov state model, on which the theory of absorbing and ergodic Markov chains is applied, and leads to a computational algorithm. The second method, which is based on a specific assumption, uses a substantially simpler stochastic model and results in equations which are easily solved by means of iterative computation. In the case of geometrically distributed interarrival times, simple analytical formulas are extracted. The results are compared to the exact ones (that is, those obtained by the first method or by extended simulation runs) and surprising agreement is observed.

Hybrid context modeling: a location-based scheme using ontologies

Context awareness is an inherent feature of pervasive computing. It enhances the proactiveness of the system thus requiring less user attention and fewer human-machine interactions, it supports intelligent personalization features, and it can assist the system to address the user requirements considering the current conditions. Nevertheless, in such environments, various types of context information are involved and need to be efficiently managed and maintained, soundly interpreted, rapidly processed, and securely disseminated by the system. Thus, an interoperable and flexible context representation scheme is necessary that will support efficient context interpretation and reasoning and will perform well in distributed large-scale context-aware systems. This paper is concerned with the development of a hybrid context representation scheme that aims to combine the maintenance, distribution and administrative facilities of a location-based context model and the semantic advantages of context ontologies

QoS awareness support in Web-Service semantics

Web Services (WSs) are a new breed of web application that have brought out quite challenging research issues. One of these is the establishment of an interoperable semantic framework suitable to represent all potential features of WSs. Apart from the functional properties that have already been modeled via standardized tools, there are also the nonfunctional features of WSs i.e. their Quality-of-Service, which in most cases are not included in the WS description. Nevertheless, integrating QoS features in WS profiles is to the advantage of both users and providers, as it supports QoS-aware WS selection and composition addressing the user’s QoS requirements, while enabling WS providers to increase their profit in the e-business domain. This paper is concerned with the creation of a QoS ontology framework adequate for WS provision. It has sprang from the work carried out in the IST-Amigo1 Integrated Project for Ambient Intelligence (AmI) homes, which aims to develop an open, standardized platform for the provision of QoSaware AmI Web Services in home environments.

Review: Traffic source models for ATM networks: a survey

Selecting appropriate models of ATM traffic sources is an inportant issue, since it is closely related to the successful design and efficient performance of the ATM networks to be built in the future. For the three basic categories of sources (voice, data and video), numerous source models have been proposed in the literature. In this paper, we summarize the main features of each of these categories, and present a survey of related models. We argue that it is preferable to select a set of standard source models rather than a single such model. We define a set of criteria to be used in the selection, and choose appropriate source models accordingly.

Context management for the provision of adaptive services to roaming users

Various types of sophisticated networks and terminals are used for the provision of thirdgeneration services, and even more complicated ones are designed for 4G systems. Roaming users will rely on new kinds of wireless networks and terminals to offer mobility and make multimedia services available everywhere. They will, of course, expect continuous access to personalized services from any place, transparently and independent of the underlying network technology and the terminal or point of access. Virtual home environment features were specified and implemented in order to satisfy these requirements in 3G systems. The enhanced role of IP in 4G systems and the assimilation of WLAN technology will enable further advances toward pervasive computing and the pursuit of corn-, plete context awareness in state-of-the-art applications and services. 4G services can he smarter and more adaptive by taking advantage of all types of context available to them within a well defined context management framework. This article presents results from work carried out over the last few years at NTUA,’ bringing us closer to the definition of such a flexible framework for cfficient management of content, which will he able to support the development of advanced telecommunications services and integrated real-time information provision and processing systems.

Traffic model for third generation cellular mobile telecommunication systems

Traffic analysis for third generation mobile telecommunication systems should take into account a variety of services (e.g., voice, data, video) and “environments” (private, public outdoor, public indoor) as well as the user mobility behavior. The analytical traffic model presented in this paper incorporates all the above mentioned features. The model utilizes a set of simplifying assumptions regarding the distribution of certain random time intervals (e.g., call duration and “cell residence time”) and the handover arrival process. The core of the model focuses on the estimation of the cell border crossing rate and the time it takes a busy mobile user to leave a cell area. This allows for the estimation of the handover rate and the call duration within a cell, which in turn, utilizing an iterative method, allows for the calculation of the offered traffic load per cell. The major advantages of the model are: (a) the simple closed form solutions, (b) its independence from the applied radio resource management scheme, and (c) its accuracy. The latter is validated via a simulation tool, which accommodates different cell-layout scenarios over a geographical area, representing a ‘typical’ city center, modeled as a Manhattan grid.

Quality of service requirements in ATM-based B-ISDNs

Abstract The purpose of this paper is to present the Quality of Service (QOS) requirements of bearer services in an ATM based B-ISDN environment. Asynchronous Transfer Mode (ATM) is a specific packet-oriented switching and multiplexing technique for carrying future broadband telecommunication services. An extremely wide variety of services with different traffic characteristics and performance requirements is expected to be supported by the ATM based B-ISDN. In this paper, the ATM QOS parameters are studied on a per service basis. For this purpose a number of characteristic bearer services has been selected, and the required values for the ATM QOS parameters for each of the selected services have been defined.

Context modelling and management in ambient-aware pervasive environments

Services in pervasive computing systems must evolve so that they become minimally intrusive and exhibit inherent proactiveness and dynamic adaptability to the current conditions, user preferences and environment. Con-text awareness has the potential to greatly reduce the human attention and interaction bottlenecks, to give the user the impression that services fade into the background, and to support intelligent personalization and adaptability features. To establish this functionality, an infrastructure is required to collect, manage, maintain, synchronize, infer and disseminate context information towards applications and users. This paper presents a context model and ambient context management system that have been integrated into a pervasive service platform. This research is being carried out in the DAIDALOS IST Integrated Project for pervasive environments. The final goal is to integrate the platform developed with a heterogeneous all-IP network, in order to provide intelligent pervasive services to mobile and non-mobile users based on a robust context-aware environment.

Utility-based RAT selection optimization in heterogeneous wireless networks

Abstract Recent technological advances in wireless networks will enable the realization of an integrated heterogeneous wireless environment consisting of multiple Radio Access Technologies (RATs) within a network provider. One of the most important benefits is that this will allow providers to balance their traffic among their subsystems without compromising on QoS issues. In this paper we focus on the Network Selection problem to allocate terminals to the most appropriate RATs by jointly examining both users’ and providers’ preferences. We introduce three utility-based optimization functions based on the type of application that users request. We then formulate the terminal assignment problem as an optimization problem, which is recognized as NP-hard. We examine both offline and online selection and develop an optimal Branch and Bound (BB) algorithm, a Greedy heuristic, as well as three Strip Packing variations. BB behaves efficiently in both offline and online environments reducing the search procedure, while the proposed heuristics produce results close to the values we get from BB but with very low computational cost.

Handover related performance of mobile communication networks

Handover is a key feature of mobile communication networks which mainly resides in the base station subsystem (BSS). Therefore the BSS design is heavily affected by handover process and vice versa. In the first part of this paper handover related performance evaluation issues are outlined. Different types of handover are taken into account. In the second part the design methodology of the base station system architecture is discussed together with some concluding remarks.<<ETX>>