14731906
Distributed admission control for anycast flows
Anycasting has recently become an important research topic, especially for replicated servers. With anycasting, applications can request the "nearest" server for provision of desired (multimedia) service. In this paper, we study efficient distributed admission control (DAC) for anycast flows. We focus on algorithms that perform destination selection and efficient path establishment. Taking advantage of anycasting, our distributed algorithms differ from each other in their dependence on system status information. Performance data obtained through mathematical analysis and simulations show that, in terms of admission probabilities, DAC systems that are based on local status information have performance levels close to those that utilize global and dynamic status information. This renders our DAC algorithms useful not only for the network layer, but also for the application layer admission control for anycast flows.
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.
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.
446110
Controlling the mobility of multiple data transport ferries in a delay-tolerant network
As technology rapidly progresses, more devices will combine both communication and mobility capabilities. With mobility in devices, we envision a new class of proactive networks that are able to adapt themselves, via physical movement, to meet the needs of applications. To fully realize these opportunities, effective control of device mobility and the interaction between devices is needed. In this paper, we consider the message ferrying (MF) scheme which exploits controlled mobility to transport data in delay-tolerant networks, where end-to-end paths may not exist between nodes. In the MF scheme, a set of special mobile nodes called message ferries are responsible for carrying data for nodes in the network. We study the use of multiple ferries in such networks, which may be necessary to address performance and robustness concerns. We focus on the design of ferry routes. With the possibilities of interaction between ferries, the route design problem is challenging. We present algorithms to calculate routes such that the traffic demand is met and the data delivery delay is minimized. We evaluate these algorithms under a variety of network conditions via simulations. Our goal is to guide the design of MF systems and understand the tradeoff between the incurred cost of multiple ferries and the improved performance. We show that the performance scales well with the number of ferries in terms of throughput, delay and resource requirements in both ferries and nodes.
45502875
DotSlash - Creating Content Distribution Networks on Demand
Traditional content distribution networks, such as Akamai, are well-suited for static web services that routinely experience large traffic volumes. They are unsuited for active content, i.e., content generated by scripts from databases, and web sites that are unlikely to receive significant number of requests. However, a few such sites will invariably experience their "fifteen minutes of fame", typically by being mentioned on a high-volume news site such as SlashDot or CNN. Such flashcrowds or "slashdot effect" will routinely cause single-server websites to collapse. We have designed and prototyped an autonomic web replication system, called DotSlash, that drafts rescue servers fully automatically, without user intervention. The system discovers suitable rescue servers via wide-area service location, either among peer servers or from a dedicated pool of rescue servers, allocates them for temporary use and redirects requests to them. The system is completely transparent to clients and does not require URL rewriting or other client modifications. We have designed two versions. The first, an Apache extension, deals only with static content, e.g., HTML pages or media objects. The second version can also replicate and execute scripts remotely. We have prototyped the system for the common LAMP (Linux, Apache, MySQL and PHP) configuration and shown that a common benchmark for bulletin boards can be replicated without code changes, yielding capacity increases bounded only by the database server. Since many such systems, including most blogs, are bottlenecked by the web server, our system can significantly increase capacity and works even for extremely rapid load increases. We are currently investigating how such systems can be further extended by increasing the database capacity of read-mostly systems with loose consistency constraints.
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.
43377675
Approximating the Medial Axis from the Voronoi Diagram with a Convergence Guarantee
We show that the medial axis of a surface S ? R3 can be approximated as a subcomplex of the Voronoi diagram of a point sample of S. The subcomplex converges to the true medial axis as the sampling density approaches infinity. Moreover, the subcomplex can be computed in a scale and density independent manner. Experimental results as detailed in a companion paper corroborate our theoretical claims.
797656
Automated glue/wrapper code generation in integration of distributed and heterogeneous software components
UniFrame is a framework to help organizations to build interoperable distributed computing systems. Using UniFrame, a new system is built by assembling predeveloped heterogeneous and distributed software components. UniFrame solves the heterogeneity problem by explicitly modeling the domain knowledge of various technology domains (component model domains, programming language domains, operating system platform domains, etc.), from which the interoperation generative domain model (IGDM) straddling the technology domains can be constructed. The glue/wrapper code that realizes the interoperation among the distributed and heterogeneous software components can be generated from the IGDM. An informal implementation in Java of glue/wrapper code generator is given, followed by a discussion on a formalization of IGDM. The formalism comes from the fact that if the family of glue/wrapper code can be modeled formally, an instance glue/wrapper code can be generated automatically. In this formalization, the IGDM is formally modeled as a language definition using a grammar; the code that realizes the interoperation is a valid sentence derivable from the grammar, and will be generated automatically from the IGDM during the assembly time.