Reliable election in broadcast networks

Election in a computer network is an operation in which one process is selected from among a group of processes to perform a particular task. An election is characterized by (1) the capacities of the candidates, and (2) the agreement reached by all processes to elect the master. In this paper, we show that election is in fact a very general style of computation. Many problems in computer networks can be solved by means of election. We then examine the election problem in computer networks with broadcast support. Basic design issues of election algorithms are addressed, and a number of election algorithms are presented based on various environments. These algorithms allow all nonfaulty processes to elect one and only one process as the master, and, by changing the definition of the capacities, they can be applied to a variety of problems.     

Optimizing routing in packet-switched networks with non-Poisson offered traffic

Routing models for packet-switched networks have traditionally been based on the assumption that the offered traffic is Poisson. This is unrealistic since for many applications, real life data streams tend to be extremely bursty, contradicting the Poisson assumption. This paper introduces a centralized bifurcated routing optimization model for networks with significantly non-Poisson offered traffic. The central purpose of the work is to assess the impact of non-Poisson traffic on routing algorithm developed for Poisson flows. A systematic testing plan for networks with a simple topology and variable levels of capacity, demand and packet length was designed. The results confirmed that Poisson delay formulas together with classical Poisson routing are not appropriate when significant demand is highly variable. The results also show that non-Poisson delay formulas are crucial to the assessment of average delay in these cases.     

Tabu search for the redundancy allocation problem of homogenous series–parallel multi-state systems

This paper develops an efficient tabu search (TS) heuristic to solve the redundancy allocation problem for multi-state series–parallel systems. The system has a range of performance levels from perfect functioning to complete failure. Identical redundant elements are included in order to achieve a desirable level of availability. The elements of the system are characterized by their cost, performance and availability. These elements are chosen from a list of products available in the market. System availability is defined as the ability to satisfy consumer demand, which is represented as a piecewise cumulative load curve. A universal generating function technique is applied to evaluate system availability. The proposed TS heuristic determines the minimal cost system configuration under availability constraints. An originality of our approach is that it proceeds by dividing the search space into a set of disjoint subsets, and then by applying TS to each subset. The design problem, solved in this study, has been previously analyzed using genetic algorithms (GAs). Numerical results for the test problems from previous research are reported, and larger test problems are randomly generated. Comparisons show that the proposed TS out-performs GA solutions, in terms of both the solution quality and the execution time.     

Topology-aware wavelength partitioning for DWDM OBS networks: A novel approach for absolute QoS provisioning

Optical Burst Switching (OBS) is a promising switching technology for the next generation all-optical networks. An OBS network without wavelength converters and fiber delay lines can be implemented simply and cost-effectively using the existing technology. However, this kind of networks suffers from a relatively high burst loss probability at the OBS core nodes. To overcome this issue and consolidate OBS networks with QoS provisioning capabilities, we propose a wavelength partitioning approach, called Optimization-based Topology-aware Wavelength Partitioning approach (OTWP). OTWP formulates the wavelength partitioning problem, based on the topology of the network, as an Integer Linear Programming (ILP) model and uses a tabu search algorithm (TS) to resolve large instances efficiently. We use OTWP to develop an absolute QoS differentiation scheme, called Absolute Fair Quality of service Differentiation scheme (AFQD). AFQD is the first absolute QoS provisioning scheme that guarantees loss-free transmission for high priority traffic, inside the OBS network, regardless of its topology. Also, we use OTWP to develop a wavelength assignment scheme, called Best Effort Traffic Wavelength Assignment scheme (BETWA). BETWA aims to reduce loss probability for best effort traffic. To make AFQD adaptive to non-uniform traffic, we develop a wavelength borrowing protocol, called Wavelength Borrowing Protocol (WBP). Numerical results show the effectiveness of the proposed tabu search algorithm to resolve large instances of the partitioning problem. Also, simulation results, using ns-2, show that: (a) AFQD provides an excellent quality of service differentiation; (b) BETWA substantially decreases the loss probability of best effort traffic to a remarkably low level for the OBS network under study; and (c) WBP makes AFQD adaptive to non-uniform traffic by reducing efficiently blocking probability for high priority traffic.