8990327
Routing algorithms for anycast messages
We propose and analyze three routing algorithms for anycast packets: source-destination based routing with weighted random selection (SD/WRS); destination based routing with weighted random selection (D/WRS); and the shortest shortest path first (SSPF) algorithms. The SSPF algorithm is a simple extension to the traditional SPF algorithm for routing unicast packets. The SD/WRS and D/WRS algorithms explicitly take into account characteristics of anycast message traffic and its recipient group. As a result, our simulation study shows that both the SD/WRS and D/WRS algorithms perform much better than SSPF in terms of average end-to-end packet delay. In particular, SD/WRS performs very close to a dynamic optimal algorithm in most cases. Our algorithms are simple, efficient and compatible with the most of existing routing technologies. We also formally prove the loop free and correctness properties for our algorithms.
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.
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.
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.
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.
17507277
Transforming business process models: enabling programming at a higher level
Two practical paradigms are presented, which facilitate domain concepts to be directly used to model business operations: the first paradigm is based on the business artifacts and their life cycle; the second paradigm is based on the business tasks and their sequencing. Transformation is an effective way to bridge the gap between business level analysis and IT solutions. We present algorithms that transform business process models based on these two paradigms into IT solutions of Web service platform. The specific problems we addressed in this transformation are: 1) how to generate the implementation code of an optimal size; 2) how to preserve the natural structure of business process models in the generated code.
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.
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
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.
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.