No abstract

In general, two types of resource reservations in computer networks can be distinguished: immediate reservations which are made in a just-in-time manner and advance reservations which allow to reserve resources a long time before they are actually used. Advance reservations are especially useful for grid computing but also for a variety of other applications that require network quality-ofservice, such as content distribution networks or even mobile clients, which need advance reservation to support handovers for streaming video. With the emerged MPLS standard, explicit routing can be implemented also in IP networks, thus overcoming the unpredictable routing behavior which so far prevented the implementation of advance reservation services. The impact of such advance reservation mechanisms on the performance of the network with respect to the amount of admitted requests and the allocated bandwidth has so far not been examined in detail. In this paper, we show that advance reservations can lead to a reduced performance of the network with respect to both metrics. The analysis of the reasons shows a fragmentation of the network resources. In advance reservation environments, additional new services can be defined such as malleable reservations which are introduced in this paper and can lead to an increased performance of the network. Four strategies for scheduling malleable reservations are presented and compared. The results of the comparisons show that some strategies increase the resource fragmentation and are therefore unsuitable in the considered environment while others lead to a significantly better performance of the network. Besides discussing the performance issue, in this paper the software architecture of a management system for advance reservations is presented.

No abstract

Abstract. Resource reservations in advance are a mature concept for the allocation of various resources, particularly in grid environments. Common grid toolkits such as Globus support advance reservations and assign jobs to resources at admission time. While the allocation mechanisms for advance reservations are available in current grid management systems, in case of failures the advance reservation perspective demands for strategies that support more than recovery of jobs or applications that are active at the time the resource failure occurs. Instead, also already admitted, but not yet started applications are affected by the failure and hence, need to be dealt with in an appropriate manner. In this paper, we discuss the properties of advance reservations with respect to failure recovery and outline a number of strategies applicable in such cases in order to reduce the impact of resource failures and outages. It can be shown that it pays to remap also affected but not yet started jobs to alternative resources if available. Alike reserving in advance, this can be considered as remapping in advance. In particular, a remapping strategy that prefers requests that were allocated a long time ago, provides a high fairness for clients as it implements similar functionality as advance reservations, while achieving the same performance as the other strategies.

No abstract