9469881
Scalable multicast routing protocol using anycast and hierarchical-trees
A novel efficient and effective Internet multicast routing protocol is presented with short delay, high throughput, resource utilization and scalability for a single multicast group g. The protocol has two features: (1) multiple shared-trees (MST) are configured to provide efficient, dynamic and quality multicast routing; (2) an anycasting approach is used to form the tree roots into an anycast group so that the multicast packets can be anycast to the nearest node at one of the shared trees to achieve the best routing service for the multicast packets. The performance of the MST protocol is analyzed through extensive simulations and compared with well-known source tree and shared-tree routing.
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>>
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.
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.
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.
16465033
Trading latency for energy in wireless ad hoc networks using message ferrying
Power management is a critical issue in wireless ad hoc networks where the energy supply is limited. In this paper, we investigate a routing paradigm, message ferrying (MF), to save energy while trading off data delivery delay. In MF, special nodes called ferries move around the deployment area to deliver messages for nodes. The reliance on the movement of ferries to deliver data increases the delivery delay. However, nodes can save energy by disabling their radios when ferries are far away. To exploit this feature, we present a power management framework, in which nodes switch their power management modes based on the knowledge of ferry location. We evaluate the performance of our scheme using ns-2 simulations and compare it with dynamic source routing (DSR). Our simulation results show that MF achieves energy savings as high as 95% compared to DSR without power management and still delivers more than 98% of data. In contrast, power-managed DSR delivers much less data than MF to achieve similar energy savings. In the scenario of heavy traffic load, power-managed DSR delivers less than 20% of data. MF also shows robust performance for highly mobile nodes, while the performance of DSR suffers significantly. Thus, delay tolerant applications should use MF rather than a multihop routing protocol to save energy efficiently when both routing approaches are available.
12760716
Making Web services dependable
Web services offer great promise for integrating and automating software applications within and between enterprises over the Internet. However, ensuring that Web services are dependable, and can satisfy their clients' requests when the clients need them is a real challenge because, typically, a business activity involves multiple Web services and a Web service involves multiple components, each of which must be dependable. In this paper, we describe fault tolerance techniques, including replication, checkpointing, and message logging, in addition to reliable messaging and transaction management for which Web services specifications exist. We discuss how those techniques can be applied to the components of the Web services involved in the business activities to render them dependable.
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.
30153007
Selective anti-entropy
Anti-entropy [1] is an important mechanism to achieve eventual consistency among a set of replicas. We refer to traditional antientropy [2, 3] as complete anti-entropy, where two replicas reconcile all inconsistent states between them in a two-way session or two one-way sessions. Complete anti-entropy works well in full replications, but may cause a summary problem (a replica cannot summarize its received updates using a summary vector) in partial replications (where the state set is divided into subsets referred to as scopes). To avoid the summary problem, we propose to use selective anti-entropy, which is to selectively reconcile inconsistent states between two replicas in a session, i.e., a replica specifies the subsets of updates it solicits, and thus controls what it receives from another replica. In selective anti-entropy, all updates that are initially received by the same replica R= belong to the same s u b s e t / ~ . The subset of a state is determined by the last update applied to it. A selective anti-entropy session where R¢ requests new updates in -P~i, Rx2, .... R~ k from R~ is denoted as O(R~, {/:/=~, Rx2, ..., R=k }, R~). We distinguish four types of selective anti-entropy sessions (listed in Figure 1) based on the number of subsets requested and whether the session is direct or indirect. We assume that a replica R¢ does not request updates in ~ from other replicas. A session is direct if it only requests updates in R--~ from R= (e.g., O___(R~, { ~ } , R~)), otherwise the session is indirect (e.g., O(R=, {1-~u}, R~)) or mixed (e.g., O(_R=, {R~, R~}, R~)). A select-multiple or select-all session can be viewed as comprising k (k >_ 2) select-one sessions, in which at most one is select-one-direct session, and the rest are select-one-indirect sessions. A select-all session is equivalent to a complete anti-entropy session. An anti-entropy session is safe if it will not cause the summary problem. A replica can always choose safe sessions by using selective anti-entropy. Any select-one-direct anti-entropy session, such as O(R=, {R~}, R~), is safe. A select-one-indirect anti-entropy session O(R=, {R-~y}, R~) is safe if S(R=) A S(Ru) C_ S(R~), where S(R=), S(Ru) and S(Rz) denote the scopes of Re, Rv and R~, respectively. In other words, if S(R=) n S(Ru) D S(R=), O(R=, {R-~}, Rz) may cause the summary problem. In Figure 2, for example, O(Ra, {R1}, R6) is safe because S(Ra) N S(R1) = {$1, $2} = S(R6) , but O(R3, {R6}, R2) may not be safe since
8961835
Design and Implementation of a Pluggable Fault-Tolerant CORBA Infrastructure
In this paper we present the design and implementation of a Pluggable Fault-Tolerant CORBA Infrastructure that provides fault tolerance for CORBA applications by utilizing the pluggable protocols framework that most CORBA ORBs provide. Our approach does not require any modification to the CORBA ORB, and requires only minimal modification to the application. Moreover, it avoids the difficulty of retrieving and assigning the ORB state by embedding the fault tolerance mechanisms into the ORB. The Pluggable Fault-Tolerant CORBA Infrastructure exhibits similar or better performance than other Fault-Tolerant CORBA systems, while providing strong replica consistency.