A Comparison of the Memory Management sub-systems in FreeBSD and Linux

In this article we seek to compare the memory management sub-systems of two popular and freely available operating systems - FreeBSD and Linux. First a framework is developed, spelling out the components of a generic and modern memory management system. The framework is then used in a design level comparison of memory management in the two operating systems. (Also cross-referenced as UMIACS-TR-98-45

Learning for Interval Prediction of Electricity Demand: A Cluster-based Bootstrapping Approach

Accurate predictions of electricity demands are necessary for managing operations in a small aggregation load setting like a Microgrid. Due to low aggregation, the electricity demands can be highly stochastic and point estimates would lead to inflated errors. Interval estimation in this scenario, would provide a range of values within which the future values might lie and helps quantify the errors around the point estimates. This paper introduces a residual bootstrap algorithm to generate interval estimates of day-ahead electricity demand. A machine learning algorithm is used to obtain the point estimates of electricity demand and respective residuals on the training set. The obtained residuals are stored in memory and the memory is further partitioned. Days with similar demand patterns are grouped in clusters using an unsupervised learning algorithm and these clusters are used to partition the memory. The point estimates for test day are used to find the closest cluster of similar days and the residuals are bootstrapped from the chosen cluster. This algorithm is evaluated on the real electricity demand data from EULR(End Use Load Research) and is compared to other bootstrapping methods for varying confidence intervals

Improving NFS Performance over Wireless Links

NFS is a widely used remote file access protocol that has been tuned to perform well on traditional LANs which exhibit low error rates. Users migrating to mobile-hosts would like to continue to use NFS for remote file accesses. However, low bandwidth and high error-rates degrade performance on mobile-hosts using wireless links thus hindering the use of NFS. In this paper, we present two mechanisms to improve NFS performance over wireless links : an aggressive NFS client and link-level retransmissions. Our experiments show that these mechanisms improve throughput by up to 200%, which brings the performance to within 5% of that obtained in zero error conditions. (Also cross-referenced as UMIACS-TR-95-126

Avoiding Instability during Graceful Shutdown of OSPF

Many recent router architectures decouple the routing engine from the forwarding engine, so that packet forwarding can continue even when the routing process is not active. This opens up the possibility of using the forwarding capability of a router even when its routing process is down, thus avoiding the route flaps that normally occur when the routing process goes down. Unfortunately, current routing protocols, such as BGP, OSPF and IS-IS do not support this behavior. In this paper, we describe an enhancement to OSPF, called the IBB (I'll Be Back) capability, that enables other routers to use a router whose OSPF process is inactive for forwarding traffic for a certain period of time. The IBB capability can be used for avoiding route flaps that occur when the OSPF process is brought down in a router to facilitate protocol software upgrade, operating system upgrade, router ID change, AS and interface renumbering, etc

Indexing Techniques in Object Oriented Databases

Object Oriented Database systems (OODBs) need efficient indexing techniques just like other Database systems. However, B -trees which work very well for Relational Database systems are not good enough for OODBs. Several alternate indexing techniques have been proposed, amongst them H-trees. This report analyses indexing techniques for OODBs, in particular H-trees. Contents 1 Introduction 4 2 CH-trees 5 3 S-trees 6 4 H-trees 10 4.1 Structure : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 10 4.2 Nesting : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 11 5 H-trees : Implementation Details 13 5.1 Node Headers : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 13 5.2 Build : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 14 5.3 Search : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 15 5.4 Insert : : : : : : : : : : : : : : : : : : : : : : ..

Reducing Router-Crossings in a Mobile Intranet

Current general purpose mobility solutions like Mobile-IP involve multiple routercrossings even when the mobile host moves within an intranet from one subnet of a router to another. An environment consisting of a large number of mobile hosts would congest the router causing hosts to experience high latency and jitter. This paper presents a mechanism to eliminate multiple router-crossings in a mobile intranet, which reduces the load on the routers and the hand-o and data latency at the mobile hosts

BGP Scaling Techniques Revisited

Introduction This note adds definitions and clarification to "A Comparison of Scaling Techniques for BGP" [1], corrects some minor errors and clarifies points which may not have been clear in the original paper. It also adds a new analysis of the scaling properties of routereflectors and confederations, leading to a new conclusion that route-reflection and confederations scale equally well in the general case and that the choice of the scaling technique employed by a network needs to be made on a basis other than the scalability metric we have analyzed. 2 Terminology [1] measures "scaling" in terms of the maximum number of BGP sessions any given router in the network must support. This is probably the best gross metric of how a BGP network scales. For convenience, we term this scaling metric the "BGP session degree" of a network. In addition, we introduce the term "CBGP" to mean "confederation-EBGP". 3 Corrections 3.1 Tree Topologies [1] states in Section 2.2 (paragraph 2) tha