560 research outputs found
Workload Equity in Vehicle Routing Problems: A Survey and Analysis
Over the past two decades, equity aspects have been considered in a growing
number of models and methods for vehicle routing problems (VRPs). Equity
concerns most often relate to fairly allocating workloads and to balancing the
utilization of resources, and many practical applications have been reported in
the literature. However, there has been only limited discussion about how
workload equity should be modeled in VRPs, and various measures for optimizing
such objectives have been proposed and implemented without a critical
evaluation of their respective merits and consequences.
This article addresses this gap with an analysis of classical and alternative
equity functions for biobjective VRP models. In our survey, we review and
categorize the existing literature on equitable VRPs. In the analysis, we
identify a set of axiomatic properties that an ideal equity measure should
satisfy, collect six common measures, and point out important connections
between their properties and those of the resulting Pareto-optimal solutions.
To gauge the extent of these implications, we also conduct a numerical study on
small biobjective VRP instances solvable to optimality. Our study reveals two
undesirable consequences when optimizing equity with nonmonotonic functions:
Pareto-optimal solutions can consist of non-TSP-optimal tours, and even if all
tours are TSP optimal, Pareto-optimal solutions can be workload inconsistent,
i.e. composed of tours whose workloads are all equal to or longer than those of
other Pareto-optimal solutions. We show that the extent of these phenomena
should not be underestimated. The results of our biobjective analysis are valid
also for weighted sum, constraint-based, or single-objective models. Based on
this analysis, we conclude that monotonic equity functions are more appropriate
for certain types of VRP models, and suggest promising avenues for further
research.Comment: Accepted Manuscrip
On green routing and scheduling problem
The vehicle routing and scheduling problem has been studied with much
interest within the last four decades. In this paper, some of the existing
literature dealing with routing and scheduling problems with environmental
issues is reviewed, and a description is provided of the problems that have
been investigated and how they are treated using combinatorial optimization
tools
On-Line End-to-End Congestion Control
Congestion control in the current Internet is accomplished mainly by TCP/IP.
To understand the macroscopic network behavior that results from TCP/IP and
similar end-to-end protocols, one main analytic technique is to show that the
the protocol maximizes some global objective function of the network traffic.
Here we analyze a particular end-to-end, MIMD (multiplicative-increase,
multiplicative-decrease) protocol. We show that if all users of the network use
the protocol, and all connections last for at least logarithmically many
rounds, then the total weighted throughput (value of all packets received) is
near the maximum possible. Our analysis includes round-trip-times, and (in
contrast to most previous analyses) gives explicit convergence rates, allows
connections to start and stop, and allows capacities to change.Comment: Proceedings IEEE Symp. Foundations of Computer Science, 200
Optimization Based Rate Control for Multicast with Network Coding
Recent advances in network coding have shown
great potential for efficient information multicasting in communication
networks, in terms of both network throughput and
network management. In this paper, we address the problem of
rate control at end-systems for network coding based multicast
flows. We develop two adaptive rate control algorithms for
the networks with given coding subgraphs and without given
coding subgraphs, respectively. With random network coding,
both algorithms can be implemented in a distributed manner, and
work at transport layer to adjust source rates and at network
layer to carry out network coding. We prove that the proposed
algorithms converge to the globally optimal solutions for intrasession
network coding. Some related issues are discussed, and
numerical examples are provided to complement our theoretical
analysis
Bandwidth sensitive routing in diffServ networks with heterogeneous bandwidth requirements
This paper studies the problem of finding optimal routes for premium class traffic in a DiffServ network such that (1) loop-freedom is guaranteed in the entire network under hop-by-hop routing assumption; and (2) the maximum relative congestion among all links is minimized. This problem is called the Extended Optimal Premium Routing (eOPR) problem, which is proven to be NP-hard. We use the integer programming method to mathematically formulate the eOPR problem and find the optimal solutions for small scale networks. We also study heuristic algorithms in order to handle large scale networks. Simulation results are compared with the optimal solutions obtained by solving the integer programming models. The results show that the Bandwidth-inversion Shortest Path (BSP) algorithm can be a good candidate to route premium traffic in DiffServ networks.published_or_final_versio
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