TOW ARDS NEW TECHNIQUES IN TELECOMMUNICATIONS TO SERVE LARGE USER POPULATIONS

An account is given in this paper of the industry oriented research at the Faculty of Electrical Engineering in the past five years in the field of Public Telecommunications and Telematics. Actual and realistically anticipated needs of the users are briefly surveyed at the outset. Facts and views, concerning specific projects and underlying methodologies, are considered. The paper was presented at a symposium, held at the Faculty of Electrical Engineering, April 19 and 20, 1983 as part of the bicentennary events at the Technical University of Budapest

Performance modelling of a multiple threshold RED mechanism for bursty and correlated Internet traffic with MMPP arrival process

Access to the large web content hosted all over the world by users of the Internet engage many hosts, routers/switches and faster links. They challenge the internet backbone to operate at its capacity to assure e±cient content access. This may result in congestion and raises concerns over various Quality of Service (QoS) issues like high delays, high packet loss and low throughput of the system for various Internet applications. Thus, there is a need to develop effective congestion control mechanisms in order to meet various Quality of Service (QoS) related performance parameters. In this paper, our emphasis is on the Active Queue Management (AQM) mechanisms, particularly Random Early Detection (RED). We propose a threshold based novel analytical model based on standard RED mechanism. Various numerical examples are presented for Internet traffic scenarios containing both the burstiness and correlation properties of the network traffic

Teaching and learning queueing theory concepts using tangible user interfaces

Tangible User Interfaces (TUI) have emerged in the past years as effective computing platforms that intertwine digital information and visualization with physical interactivity. Whilst successfully capitalizing on these properties within primary education to engage and educate children in an entertaining manner, TUI systems have seen limited deployment in more complex scenarios. To this end, this paper investigates the aptness and effectiveness of implementing TUI systems to enhance teaching and learning within higher educational institutes in order to aid the understanding of complex and abstract concepts. The proposal augments mere simulation processes by developing a table-top architecture to allow the real-time interaction and visualization of queuing theory concepts. The paper describes the deployment of the TUI framework within an undergraduate computer networks degree whereby the quantitative effectiveness of this system is assessed from a teaching and learning perspective within an engineering pedagogy

Stochastic Dynamic Programming and Stochastic Fluid-Flow Models in the Design and Analysis of Web-Server Farms

A Web-server farm is a specialized facility designed specifically for housing Web servers catering to one or more Internet facing Web sites. In this dissertation, stochastic dynamic programming technique is used to obtain the optimal admission control policy with different classes of customers, and stochastic uid- ow models are used to compute the performance measures in the network. The two types of network traffic considered in this research are streaming (guaranteed bandwidth per connection) and elastic (shares available bandwidth equally among connections). We first obtain the optimal admission control policy using stochastic dynamic programming, in which, based on the number of requests of each type being served, a decision is made whether to allow or deny service to an incoming request. In this subproblem, we consider a xed bandwidth capacity server, which allocates the requested bandwidth to the streaming requests and divides all of the remaining bandwidth equally among all of the elastic requests. The performance metric of interest in this case will be the blocking probability of streaming traffic, which will be computed in order to be able to provide Quality of Service (QoS) guarantees. Next, we obtain bounds on the expected waiting time in the system for elastic requests that enter the system. This will be done at the server level in such a way that the total available bandwidth for the requests is constant. Trace data will be converted to an ON-OFF source and fluid- flow models will be used for this analysis. The results are compared with both the mean waiting time obtained by simulating real data, and the expected waiting time obtained using traditional queueing models. Finally, we consider the network of servers and routers within the Web farm where data from servers flows and merges before getting transmitted to the requesting users via the Internet. We compute the waiting time of the elastic requests at intermediate and edge nodes by obtaining the distribution of the out ow of the upstream node. This out ow distribution is obtained by using a methodology based on minimizing the deviations from the constituent in flows. This analysis also helps us to compute waiting times at different bandwidth capacities, and hence obtain a suitable bandwidth to promise or satisfy the QoS guarantees. This research helps in obtaining performance measures for different traffic classes at a Web-server farm so as to be able to promise or provide QoS guarantees; while at the same time helping in utilizing the resources of the server farms efficiently, thereby reducing the operational costs and increasing energy savings

Methodologies synthesis

This deliverable deals with the modelling and analysis of interdependencies between critical infrastructures, focussing attention on two interdependent infrastructures studied in the context of CRUTIAL: the electric power infrastructure and the information infrastructures supporting management, control and maintenance functionality. The main objectives are: 1) investigate the main challenges to be addressed for the analysis and modelling of interdependencies, 2) review the modelling methodologies and tools that can be used to address these challenges and support the evaluation of the impact of interdependencies on the dependability and resilience of the service delivered to the users, and 3) present the preliminary directions investigated so far by the CRUTIAL consortium for describing and modelling interdependencies

Queue Management Performance Evaluation of REM, GRED, and DropTail Algorithms

As the new user applications and Internet traffic are increased rapidly Rapid growth, the need for developing the Internet infrastructure that guarantee good level of quality of service became necessary. Congestion that is caused by uncontrollable amount of traffic remains as a main problem that threats the Quality of Service (QoS) on the Internet. Proactive Queue Management Mechanisms employed in the Internet routers help in improving the performance of responsive applications such as TCP applications. The selection of Active queue management mechanism plays an important role that leads to well network performance and utilization. In this project, we performance evaluation for examining the performance of the some of the known queue management mechanisms, namely DropTail, REM, and RED proposed for IP routers to achieve performance among competing sources. The purpose of this performance examination is to identify the key parameters to improve the fairness and link utilization in TCP/IP networks. In addition, this will help obtaining a better understanding of these mechanisms by identifying and clarifying factors that influence their performance in order to improve TCP/IP networks performance overall