11059176
Policy-based validation of SAN configuration
Historically, storage has been directly connected to servers for fast local access and easy configuration. In recent years, storage area networks (SANs) have defined an alternative storage paradigm that allows storage to be shared among servers using fast interconnects. One of the key challenges of SAN management is the large number of configuration problems that are encountered in a typical SAN deployment. These configuration problems can be addressed by SAN management software. However, hard-coding the SAN configuration rules into the management software is not a viable option since it is not possible to easily modify or replace old configuration rules and specify new policies and guidelines. In this paper, we propose a novel policy-based SAN configuration validation system that can be used to specify, store, and evaluate configuration policies for SANs. We also introduce five new operators for collection policies that are useful for evaluating a wide variety of practical SAN configuration policies found in practice. The policy-based SAN configuration checking approach proposed in this paper is discussed within the context of device interoperability constraints. However, this approach is extensible as it can also be used to enforce performance, reliability, and security-related configuration constraints.
13652126
Using certes to infer client response time at the web server
As businesses continue to grow their World Wide Web presence, it is becoming increasingly vital for them to have quantitative measures of the mean client perceived response times of their web services. We present Certes (CliEnt Response Time Estimated by the Server), an online server-based mechanism that allows web servers to estimate mean client perceived response time, as if measured at the client. Certes is based on a model of TCP that quantifies the effect that connection drops have on mean client perceived response time by using three simple server-side measurements: connection drop rate, connection accept rate and connection completion rate. The mechanism does not require modifications to HTTP servers or web pages, does not rely on probing or third party sampling, and does not require client-side modifications or scripting. Certes can be used to estimate response times for any web content, not just HTML. We have implemented Certes and compared its response time estimates with those obtained with detailed client instrumentation. Our results demonstrate that Certes provides accurate server-based estimates of mean client response times in HTTP 1.0/1.1 environments, even with rapidly changing workloads. Certes runs online in constant time with very low overhead. It can be used at websites and server farms to verify compliance with service level objectives.
6124477
A counterexample to a Voronoi region conjecture
Given a 2D-symmetric lattice /spl Lambda/, it was conjectured by Forney (1989) that the projection of the Voronoi region R(/spl Lambda/) onto two coordinates equals the Voronoi region of the constituent 2D-sublattice /spl Lambda//spl nu//sub 2/. We present a three-dimensional counterexample. >
14060994
On nearest neighbor indexing of nonlinear trajectories
In recent years, the problem of indexing mobile objects has assumed great importance because of its relevance to a wide variety of applications. Most previous results in this area have proposed indexing schemes for objects with linear trajectories in one or two dimensions. In this paper, we present methods for indexing objects with nonlinear trajectories. Specifically, we identify a useful condition called the convex hull property and show that any trajectory satisfying this condition can be indexed by storing a careful representation of these objects in a traditional index structure. Since a wide variety of relevant nonlinear trajectories satisfy this condition, our result significantly expands the class of trajectories for which nearest neighbor indexing schemes can be devised. We also show that even though many non-linear trajectories do not satisfy the convex hull condition, an approximate representation can often be found which satisfies it. We discuss examples of techniques which can be utilized to find representations that satisfy the convex hull property. We present empirical results to demonstrate the effectiveness of our indexing method.
21366301
The EM Side-Channel(s)
We present results of a systematic investigation of leakage of compromising information via electromagnetic (EM) emanations from CMOS devices. These emanations are shown to consist of a multiplicity of signals, each leaking somewhat different information about the underlying computation. We show that not only can EM emanations be used to attack cryptographic devices where the power side-channel is unavailable, they can even be used to break power analysis countermeasures.
12715963
Multiple-antenna signal constellations for fading channels
In this correspondence, we show that the problem of designing efficient multiple-antenna signal constellations for fading channels can be related to the problem of finding packings with large minimum distance in the complex Grassmannian space. We describe a numerical optimization procedure for finding good packings in the complex Grassmannian space and report the best signal constellations found by this procedure. These constellations improve significantly upon previously known results.
36917414
Performance Analysis of Single Stage Interconnection Networks
A single-stage interconnection network (SSIN) consisting of only one stage of switches and recirculation through processors is studied. An analytical probability model for SSINs using 2*2 switches is introduced, and results obtained with the model are compared with simulation results. Four SSINs with different network sizes, loading, and routing strategies are discussed. Processors with and without buffers are considered, and three different routing strategies are applied to resolve conflicts. The analytical model is seen to be in close agreement with the simulation results while providing at least an order of magnitude reduction in CPU time. >
29269446
A Novel Optimal Channel Partitioning Algorithm for Integrated Wireless and Mobile Networks
How to efficiently support multi-class services is a very important issue in integrated wireless and mobile networks because each type of services has distinct characteristics and quality of service (QoS) requirements. This paper presents an efficient algorithm for near optimal channel allocation when different types of services are to be provided in the next generation integrated wireless and mobile networks. We specifically propose a preemptive priority scheme for an integrated wireless and mobile network by first dividing channels into three independent groups and classifying traffic into four different types. The proposed system is modeled by a multi-dimension Markov chain model. Then such a model is used to obtain a set of relations that correlate performances with various system parameters. A novel recursive algorithm is developed to determine the minimal number of channels in each channel group that would be necessary to satisfy the QoS requirements. We also investigate the impact of load ratio for different types of traffic on channel assignment. Finally, we discuss some limitations of our approach and indicate possible future work. We believe that the partitioning scheme proposed in this paper can become a starting point for analysis of future integrated wireless and mobile networks.
1710599
Exploiting Mobility Patterns to Reduce Re-Authentication Overheads in Infrastructure WLAN Networks
The current EAP-TLS standard accounts for authentication delays of the order of one second for infrastructure 802.11 networks. This delay is clearly unacceptable for maintaining the QoS requirements for a mobile station which have frequent handoffs to different regions. Pre-authentication schemes have been proposed to reduce these delays. However, most of these schemes suffer from an increased network message overhead since they fail to appropriately model the mobility of each individual user. In this paper, we exploit the notion of predictability in user mobility patterns and propose a set of novel proactive key distribution algorithms to achieve low latencies while minimizing the message overhead. Our schemes involve pre-distributing keys in fewer necessary access points (APs) as opposed to all neighboring APs. We evaluate the performance of our schemes for three different mobility models; (i) predictable motion (ii) changing predictable motion and (iii) random motion. Almost under all scenarios, our schemes indicate up to 70% message reduction, while maintaining similar latencies
43330192
Impact of bursty error rates on the performance of wireless local area network (WLAN)
Abstract With an increasing popularity of DCF based wireless LAN, the modeling of 802.11 distributed coordination function (DCF) has attracted lots of research attention. Existing analysis of 802.11 DCF has been focused on the determination of the throughput and the packet delay under saturated traffic and ideal channel conditions. Although some recent papers address the saturated performance under a simple uniform error model, they can hardly capture the impact of bursty characteristics of wireless fading on the performance of 802.11 DCF. This paper presents exact formulae for the throughput and the delay in DCF for various traffic conditions when either saturated or unsaturated traffic load is present. A two-state Markov channel model is incorporated to present the bursty characteristics of channel errors. With our analysis, the impact of bursty channel error on unsuccessful transmission probability and the DCF performance can be determined. The results of our analytical framework reveal that the four-way handshaking scheme does not improve throughput substantially for light traffic load. However, for heavy traffic load, the four-way handshaking scheme is advantageous as compared to the basic access scheme. Also, extensive simulation is done to substantiate the accuracy of our analytical model.
12552557
Minimizing the effect of deafness and hidden terminal problem in wireless ad hoc networks using directional antennas
In this work we addresses the issue of deafness and hidden terminal problem in Mobile Ad Hoc Networks (MANETs) using directional antennas. To minimize these effects, we propose a MAC protocol for directional Antennas (MDA) 5 which employs a novel Enhanced Directional Network Allocation Vector (EDNAV) scheme and, and an efficient technique of Diametrically Opposite Directions (DOD) transmission of RTS and CTS. We compare MDA with IEEE 802.11 and two recently proposed directional MAC schemes and results show that MDA outperforms these protocols in the majority of scenarios investigated. We also point out that the performance does depend on the network topology and the traffic pattern.