11577356
Efficient Internet Multicast Routing Using Anycast Path Selection
A novel efficient and dynamic multicast routing protocol based on anycast routing techniques is presented. The contributions of the protocol differ from well-known shared-tree systems in two aspects: (1) Off-tree anycast routing: The nodes in the shared tree are formed into a virtual anycast group and multicast sources use anycast routing to select a better path from the source to one router in the group to achieve short delay and fault-tolerance. (2) On-tree dynamic routing: The shared-tree approach is extended with capability of alternative path selections. If a node becomes absent from the shared tree, some predefined backup path(s) is (are) used to bypass the node and enable dynamic multicast routing to continue. The protocol requires only the routers near the faulty node to be reconfigured, thus reducing the runtime overhead as compared with global reconfiguration. The simulation data demonstrates the efficiency of our routing protocol.
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>>
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.
12365152
A multi-access window protocol for transmission of time constrained messages
A novel window protocol for transmitting time-constrained messages in a multiaccess network is proposed that explicitly takes time constraints into account. The window is formed on the basis of latest time to send a message (LS). A newly arriving message is immediately considered for transmission if its LS is less than those of the all pending messages in the system. As a result, the protocol closely approximates the optimal minimum-laxity-first policy. A performance evaluation by simulation shows that the protocol performs well in a wide range of environments, even under overloaded conditions.<<ETX>>
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.
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.
2955672
Grammatically Interpreting Feature Compositions
Abstract : Feature modeling is a popular domain analysis method for describing the commonality and variability among the domain products. The current formalisms of feature modeling do not have enough support for automated domain product configuration and validation. We have developed a theory of feature modeling: a feature model is analogous to a definition of a language; a particular feature composition instance (domain product) is analogous to a program written in that language; and the way the features can be assembled to form a product is analogous to the way various tokens can be assembled to form a program. To apply this theory, we have developed a meta-language Two-Level Grammar++ to specify feature models. The interpreter derived from the feature model specification performs automated product configuration and product quality validation.
11584663
Deterministic scheduling for multithreaded replicas
Replication of objects, processes and components is essential for building reliable distributed systems. However, maintaining replica consistency in the presence of nondeterminism is a challenge. There are many sources of nondeterminism in the applications being replicated. In this paper, we focus on the nondeterminism resulting from multithreading in the applications, and present a deterministic scheduling algorithm for ensuring consistent execution of replicated multithreaded applications.
9212782
A reservation-based coordination protocol for Web services
Traditional transaction semantics are not appropriate for business activities that involve long-running transactions in a loosely-coupled distributed environment, in particular, for Web services that operate between different enterprises over the Internet. In this paper we describe a novel reservation-based extended transaction protocol that can be used to coordinate such business activities. The protocol avoids the use of compensating transactions, which can result in undesirable effects. In our protocol, each task within a business activity is executed as two steps. The first step involves an explicit reservation of resources. The second step involves the confirmation or cancellation of the reservation. Each step is executed as a separate traditional short-running transaction. We show how our protocol can be implemented as a reservation protocol on top of the Web services transaction specification or, alternatively, as a coordination protocol on top of the Web services coordination specification.
9589474
DotSlash: A Self-Configuring and Scalable Rescue System for Handling Web Hotspots Effectively
DotSlash allows different web sites to form a mutual-aid community, and use spare capacity in the community to relieve web hotspots experienced by any individual site. As a rescue system, DotSlash intervenes when a web site becomes heavily loaded, and is phased out once the workload returns to normal. It aims to complement the existing web server infrastructure to handle short-term load spikes effectively. DotSlash is self-configuring, scalable, cost-effective, easy to use, and transparent to clients. It targets small web sites, although large web sites can also benefit from it. We have implemented a prototype of DotSlash on top of Apache. Experiments show that using DotSlash a web server can increase the request rate it supported and the data rate it delivered to clients by an order of magnitude, even if only HTTP redirect is used. Parts of this work may be applicable to other services such as Grid computational services.
17989665
Message ferrying: proactive routing in highly-partitioned wireless ad hoc networks
An ad hoc network allows devices with wireless interfaces to communicate with each other without any pre-installed infrastructure. Due to node mobility, limited radio power, node failure and wide deployment area, ad hoc networks are often vulnerable to network partitioning. A number of examples are in battlefield, disaster recovery and wide area surveillance. Unfortunately, most existing ad hoc routing protocols will fail to deliver messages under these circumstances since no route to the destination exists. In this work we propose the Message Ferrying or MF scheme that provides efficient data delivery in disconnected ad hoc networks. In the MF scheme, nodes move proactively to send or receive messages. By introducing non-randomness in a node's proactive movement and exploiting such nonrandomness to deliver messages, the MF scheme improves data delivery performance in a disconnected network. In this paper, we propose the basic design of the MF scheme and develop a general framework to classify variations of MF systems. We also study ferry route design problem in stationary node case which is shown to be NP-hard and provide an efficient algorithm to compute ferry route.