2266795
Response time analysis for distributed real-time systems with bursty job arrivals
This paper presents a new schedulability analysis methodology for distributed hard real-time systems with bursty job arrivals. The schedulability is analyzed by comparing worst-case response times of jobs with their timing constraints. We compute response times with a new method, which uses the amount of received service time to determine the response time of instances of a job. We illustrate how this method can be applied to exactly determine worst-case response times for processors with preemptive static priority schedulers, and how it gives a good approximation on the response times for processors with non-preemptive static-priority scheduling or first-come-first-served scheduling. Our schedulability analysis method is the first to support systems with arbitrary job arrival patterns. Nevertheless, it performs better than other known approaches used for systems with periodic job arrivals.
35665703
Implementation of QoS-Provisioning system for voice over IP
In this paper, we address issues related to implementing Voice-over-IP (VoIP) services in packet switching networks. VoIP has been identified as a critical real-time application in the network QoS research community and has been implemented in commercial products. To provide competent quality of service for VoIP, the call admission control (CAC) mechanism has to be introduced to prevent packet losing and over-queuing. Several well-designed CAC mechanisms, such as the Site- Utilization-Based CAC and the link-utilization-based CAC mechanisms, are in place. However, the existing commercial VoIP systems have not been able to adequately apply and support these CAC mechanisms, and hence unable to provide QoS guarantees to VoIP. We have designed and implemented a QoS-Provisioning system that can be seamlessly integrated to the existing VoIP system to overcome its weakness in offering QoS guarantees. As a result, our system has been realized at Internet2 Voice Over IP Testbed in Texas A&M University.
14217231
Scheduling Tasks with Resource Requirements in Hard Real-Time Systems
This paper describes a heuristic approach for solving the problem of dynamically scheduling tasks in a real-time system where tasks have deadlines and general resource requirements. The crux of our approach lies in the heuristic function used to select the task to be scheduled next. The heuristic function is composed of three weighted factors. These factors explicitly consider information about real-time constraints of tasks and their utilization of resources. Simulation studies show that the weights for the various factors in the heuristic function have to be fine-tuned in order to obtain a degree of success in the range of 75-88 percent of that obtained via exhaustive search. However, modifying the approach to use limited backtracking improves the degree of success substantially to as high as 99.5 percent. This improvement is observed even when the initial set of weights are not tailored for a particular set of tasks. Simulation studies also show that in most cases the schedule determined by the heuristic algorithm is optimal or close to optimal.
38045083
Guarantee protocols for communication in distributed hard real-time systems
A classification scheme is proposed which divides real-time messages into three different classes according to the impact on system performance when the deadline of a message is missed. A study is made of several multiaccess protocols that take into account the time constraints of messages as well as their classifications and that are able to given an early notice when an important message will miss its deadline. The performances of these protocols are evaluated and compared through simulation.<<ETX>>
3436856
Distributed Privacy Preserving Information Sharing
In this paper, we address issues related to sharing information in a distributed system consisting of autonomous entities, each of which holds a private database. Semi-honest behavior has been widely adopted as the model for adversarial threats. However, it substantially underestimates the capability of adversaries in reality. In this paper, we consider a threat space containing more powerful adversaries that includes not only semi-honest but also those malicious adversaries. In particular, we classify malicious adversaries into two widely existing subclasses, called weakly malicious and strongly malicious adversaries, respectively. We define a measure of privacy leakage for information sharing systems and propose protocols that can effectively and efficiently protect privacy against different kinds of malicious adversaries.
3254470
Providing absolute differentiated services with statistical guarantees in static-priority scheduling networks
The authors propose and analyze a methodology for providing absolute differentiated services with statistical performance guarantees for real time applications in networks that use static priority schedulers. We extend previous work on delay analysis and develop a method that can be used to derive statistical delay guarantees in a flow-unaware fashion. While traditional delay analysis methods depend on flow population information, we have developed a method that relies on network (re-)configuration time analysis, and that allows us to analyze the delays without depending on the dynamic status of flow population. With this new method, we are able to reduce the runtime admission control to a simple utilization test. No explicit delay computation is necessary at admission time, making this approach scalable to large systems.
16513442
DotSlash: Handling Web Hotspots at Dynamic Content Web Sites
We propose DotSlash, a self-configuring and scalable rescue system, for handling web hotspots at dynamic content Web sites. To support load migration for dynamic content, an origin Web server sets up needed rescue servers drafted from other Web sites on the fly, and those rescue servers retrieve the scripts dynamically from the origin Web server, cache the scripts locally, and access the corresponding database server directly. We have implemented a prototype of DotSlash for the LAMP configuration, and tested our implementation using the RUBBoS bulletin board benchmark. Experiments show that by using DotSlash a dynamic content web site can completely remove its web server bottleneck, and can support a request rate constrained only by the capacity of its database server.
2261294
Predicting the Upper Bound of Web Traffic Volume Using a Multiple Time Scale Approach
This paper presents a prediction algorithm for estimating the upper bound of future Web traffic volume. Unlike traditional traffic predictions that are performed at a single time scale using curve fitting, we employ a multiple time scale approach and utilize traffic statistical properties to do forecasting. We have applied our prediction algorithm to the 1998 World Cup data set. Experiments show that it is effective for short term traffic bound predictions, applicable to bursty traffic, and useful for Web server overload prevention.
16064988
Enhancing Service Location Protocol for efficiency, scalability and advanced discovery
This paper presents three new mechanisms for the Service Location Protocol (SLP): mesh enhancement, preference filters and global attributes. The mesh enhancement simplifies Service Agent (SA) registrations and improves consistency among Directory Agents (DAs) by defining an interaction scheme for DAs and supporting automatic registration distribution among peer DAs. Preference filters facilitate processing of search results (e.g., finding the best match) in SLP servers (DAs and SAs) to reduce the amount of data transferred to the client for saving network bandwidth. Global attributes allow using a single query to search services across multiple types. These mechanisms can improve SLP efficiency and scalability and support advanced discovery such as discovering multi-access-point services and multi-function devices. We expect that these techniques can also be applied to other service discovery systems.
41957109
End-to-end latency of a fault-tolerant CORBA infrastructure
This paper presents measured probability density functions (pdfs) for the end-to-end latency, of two-way, remote method invocations from a CORBA client to a replicated CORBA server in a fault-tolerance infrastructure. The infrastructure uses a multicast group-communication protocol based on a logical token-passing ring imposed on a single local-area network. The measurements show that the peaks of the pd/s for the latency are affected by the presence of duplicate messages for active replication, and by the position of the primary server replica on the ring for semi-active and passive replication. Because a node cannot broadcast a user message until it receives the token, up to two complete token rotations can contribute to the end-to-end latency seen by the client for synchronous remote method invocations, depending on the server processing time and the interval between two consecutive client invocations. For semi-active and passive replication, careful placement of the primary server replica is necessary to alleviate this broadcast delay to achieve the best possible end-to-end latency. The client invocation patterns and the server processing time must be considered together to determine the most favorable position for the primary replica. Assuming that an effective sending-side duplicate suppression mechanism is implemented, active replication can be more advantageous than semi-active and passive replication because all replicas compete for sending and, therefore, the replica at the most favorable position will have the opportunity to send first.
205343629
A network flow approach to the Minimum Common Integer Partition Problem
In the k-Minimum Common Integer Partition Problem, abbreviated as k-MCIE we are given k multisets X1,...,Xk of positive integers, the goal is to find an integer multiset T of the minimum size such that for every i, we can partition each of the integers in Xi so that the disjoint (multiset) union of their partitions equals T. This problem has applications in computational molecular biology, in particular, ortholog assignment and DNA hybridization fingerprint assembly. The problem is known to be NP-hard for any k ≥ 2. In this article, we improve the approximation ratio for k-MCIP by viewing this problem as a flow decomposition problem in some flow network. We show an efficient 0.5625k-approximation algorithm, improving upon the previously best known 0.6139k-approximation algorithm for this problem.