Network Links (network + link)

Distribution by Scientific Domains

Selected Abstracts

Network service scheduling and routing

G. Groves
Abstract Real-life vehicle routing problems generally have both routing and scheduling aspects to consider. Although this fact is well acknowledged, few heuristic methods exist that address both these complicated aspects simultaneously. We present a graph theoretic heuristic to determine an efficient service route for a single service vehicle through a transportation network that requires a subset of its edges to be serviced, each a specified (potentially different) number of times. The times at which each of these edges are to be serviced should additionally be as evenly spaced over the scheduling time window as possible, thus introducing a scheduling consideration to the problem. Our heuristic is based on the tabu search method, used in conjunction with various well-known graph theoretic algorithms, such as those of Floyd (for determining shortest routes) and Frederickson (for solving the rural postman problem). This heuristic forms the backbone of a decision support system that prompts the user for certain parameters from the physical situation (such as the service frequencies and travel times for each network link as well as bounds in terms of acceptability of results) after which a service routing schedule is suggested as output. The decision support system is applied to a special case study, where a service routing schedule is sought for the South African national railway system by Spoornet (the semi-privatised South African national railways authority and service provider) as part of their rationalisation effort, in order to remain a lucrative company. [source]

Porting and performance aspects from IPv4 to IPv6: The case of OpenH323

Ch. Bouras
Abstract This paper is a summary of our experiences on a case study for porting applications to IPv6. We present the results of the effort to port OpenH323, an open-source H.323 platform to IPv6, which we believe can serve as guidelines for other projects with similar goals. We briefly present the structure of the OpenH323 platform. We also discuss a number of issues arising during the porting of a platform to IPv6, like which would be the easiest approach to the porting procedure, how compatibility with earlier, IPv4-only versions of the platform could be retained, if there are any useful tools for assisting this task, how and when one could be positive that the necessary modifications had been made, and which testing procedures should be followed. We then present a variety of experiments that we conducted in order to comparatively evaluate the IPv4 and IPv6 protocol stacks. We also present the results of some initial experiments comparing IPv4 and IPv6 performance under congested network links and the conclusions that they lead us to. Copyright 2005 John Wiley & Sons, Ltd. [source]

Non-inferior Nash strategies for routing control in parallel-link communication networks

Yong Liu
Abstract We consider a routing control problem of two-node parallel-link communication network shared by competitive teams of users. Each team has various types of entities (traffics or jobs) to be routed on the network. The users in each team cooperate for the benefit of their team so as to achieve optimal routing over network links. The teams, on the other hand, compete among themselves for the network resources and each has an objective function that relates to the overall performance of the network. For each team, there is a centralized decision-maker, called the team leader or manager, who coordinates the routing strategies among all entities in his team. A game theoretic approach to deal with both cooperation within each team and competition among the teams, called the Non-inferior Nash strategy, is introduced. Considering the roles of a group manager in this context, the concept of a Non-inferior Nash strategy with a team leader is introduced. This multi-team solution provides a new framework for analysing hierarchically controlled systems so as to address complicated coordination problems among the various users. This strategy is applied to derive the optimal routing policies for all users in the network. It is shown that Non-inferior Nash strategies with a team leader is effective in improving the overall network performance. Various types of other strategies such as team optimization and Nash strategies are also discussed for the purpose of comparison. Copyright 2005 John Wiley & Sons, Ltd. [source]

A reliability-based network design problem

Piya Chootinan
Abstract This paper presents a reliability-based network design problem. A network reliability concept is embedded into the continuous network design problem in which travelers' route choice behavior follows the stochastic user equilibrium assumption. A new capacity-reliability index is introduced to measure the probability that all of the network links are operated below their capacities when serving different traffic patterns deviating from the average condition. The reliability-based network design problem is formulated as a bi-level program in which the lower level sub-program is the probit-based stochastic user equilibrium problem and the upper level sub-program is the maximization of the new capacity reliability index. The lower level sub-program is solved by a variant of the method of successive averages using the exponential average to represent the learning process of network users on a daily basis that results in the daily variation of traffic-flow pattern, and Monte Carlo stochastic loading. The upper level sub-program is tackled by means of genetic algorithms. A numerical example is used to demonstrate the concept of the proposed framework. [source]

Online supportive interactions: Using a network approach to examine communication patterns within a psychosis social support group in Taiwan

Hui-Jung Chang
A network approach was used to determine the overall supportive communication patterns constructed within the PTT psychosis support group in Taiwan, the largest bulletin board system in the Chinese-speaking world. The full sequences of supportive interactions were observed over a -year period from February 2004 to July 2006. The results indicated that the most exchanged support types were information and network links. All types of supportive communication networks were relatively sparse, yet small groups of cliques with different provision of support types formed within the psychosis group. Most of the online supportive interactions exchanged at dyadic and triadic levels. The overall supportive network was highly centralized. The overall findings with implications for future studies were discussed. [source]