Analysis of algorithms for online routing and scheduling in networks

We study situations in which an algorithm must make decisions about how to best route and schedule data transfer requests in a communication network before each transfer leaves its source. For some situations, such as those requiring quality of service guarantees, this is essential. For other situations, doing work in advance can simplify decisions in transit and increase the speed of the network. In order to reflect realistic scenarios, we require that our algorithms be online, or make their decisions without knowing future requests. We measure the efficiency of an online algorithm by its competitive ratio, which is the maximum ratio, over all request sequences, of the cost of the online algorithm\u27s solution to that of an optimal solution constructed by knowing all the requests in advance.;We identify and study two distinct variations of this general problem. In the first, data transfer requests are permanent virtual circuit requests in a circuit-switched network and the goal is to minimize the network congestion caused by the route assignment. In the second variation, data transfer requests are packets in a packet-switched network and the goal is to minimize the makespan of the schedule, or the time that the last packet reaches its destination. We present new lower bounds on the competitive ratio of any online algorithm with respect to both network congestion and makespan.;We consider two greedy online algorithms for permanent virtual circuit routing on arbitrary networks with unit capacity links, and prove both lower and upper bounds on their competitive ratios. While these greedy algorithms are not optimal, they can be expected to perform well in many circumstances and require less time to make a decision, when compared to a previously discovered asymptotically optimal online algorithm. For the online packet routing and scheduling problem, we consider an algorithm which simply assigns to each packet a priority based upon its arrival time. No packet is delayed by another packet with a lower priority. We analyze the competitive ratio of this algorithm on linear array, tree, and ring networks

Packet Routing via Min-Cost Circuit Routing

In this paper we initiate the study of competitive on-line packet routing algorithms. At any time, any network node may initiate sending a packet to another node. Our goal is to route these packets through the network, while simultaneously minimizing link bandwidth, buffer usage, and the average delay of a packet. We give efficient centralized on-line packet routing algorithms in this setting. These algorithms achieve a constant competitive ratio with respect to the average delay while increasing the link bandwidth by no more than a logarithmic factor. To obtain our packet routing results, we introduce competitive algorithms for a new problem called min-cost load circuit routing. Here, the goal is to create on-line virtual circuits in a graph, while trying to simultaneously minimize link bandwidth and (related) communication costs. 1. Introduction In this paper we initiate the study of competitive on-line packet routing algorithms. We consider a network where at any point in time, a..