9337287
Detection and Recovery for Disconnection Failures in a Web-based Medical Teleconsultation System
With the progress of advanced technology, people anticipate better quality in the medical health care service. Due to more robust requirements in medical environments, higher availability and reliability are expected. This paper describes a recovery scheme for disconnection failures in a Web-based medical teleconsultation system. With the support, the disconnected clients can re-enter the system to resume the unfinished discussion using the synchronization mechanisms. The experiments have shown that the mechanism performed successfully. The lazy synchronization further reduced the required time that the clients had to wait for joining the consultation after network disconnections
34878054
Improving Data Transmission with Helping Nodes for Geographical Ad Hoc Routing
Ad hoc networks have been extensively deployed in recent years. In such networks, obtaining a high efficiency is difficult to achieve due to mobility. Many routing approaches have been proposed to improve the performance of ad hoc networks, including table-driven and demand-driven routing protocols. Geographic routing provides a suitable solution for large-scale and dynamic networks, and reduces link failure problems during packet routing. In wireless networks, nodes movement may cause a network partition, which hinders both data transmission and information availability within the network. Several schemes have been proposed for resolving the partition problem in wireless ad hoc networks. In general, the previous solutions either relied on the use of mobile devices with known trajectories or introduced additional specific mobile nodes. By contrast, this paper proposes a scheme for overcoming the problem of network partitions using only the available devices in the environment. With the scheme, the source node searches for another mobile node, designated as the helping node, which is able to meet the destination. The selected mobile node then carries the packet toward the destination. If the helping node changes its trajectory before it forwards the packet to the destination node, a hand-off scheme is activated and the data packet is transferred to another mobile node for onward transmission
16192278
A distributed location service for reducing query failures in geographic ad hoc routing
Location service support is required for mobile nodes using geographic ad hoc routing. The mobile nodes need location information of destinations for sending data packets. Due to mobility or node failures, queries to the location servers may not always succeed. This paper presents a distributed location service (DLS) that employs dual servers to maintain position information of mobile nodes and to achieve efficient performance. With the scheme, the number of failed queries, including no response and erroneous results, can be reduced. DLS has been implemented and evaluated using the ns2 simulator. The experimental results show that DLS not only improved service availability but also location query latency.
12857629
Simple Proof Techniques for Property Preservation via Simulation
Let s1 and s2 be two reactive systems related by simulation. For what kind of properties φ can one infer s1 ≒ φ (s1 satisfies φ) from s2 ≒ φ, or vice versa? This problem has been treated in the literature for various logics in which to express φ. In this paper we make two simple observations by which such results can be proved very easily: 
1. 
(1) proofs of property preservation can be made compositional, and 
 
2. 
(2) infinitary logics are very expressive. Neither observation is new, but together they yield modular proofs of nontrivial results.
41218825
Relaxed game chromatic number of graphs
This paper discusses a coloring game on graphs. Let k, d be non-negative integers and C a set of k colors. Two persons, Alice and Bob, alternately color the vertices of G with colors from C, with Alice having the first move. A color i is legal for an uncolored vertex x if by coloring x with color i, the subgraph of G induced by those vertices of color i has maximum degree at most d. Each move of Alice or Bob colors an uncolored vertex with a legal color. The game is over if either all vertices are colored, or no more vertices can be colored with a legal color. Alice's goal is to produce a legal coloring which colors all the vertices of G, and Bob's goal is to prevent this from happening. We shall prove that if G is a forest, then for k = 3, d ≥ 1, Alice has a winning strategy. If G is an outerplanar graph, then for k = 6 and d ≥ 1, Alice has a winning strategy.
37293977
Mechanical Verification of Distributed Algorithms in Higher-Order Logic
The only way to verify the correctness of a distributed algorithm with a high degree of confidence is to construct a correctness proof that is so formal and rigorous as to be checkable by a machine. The chief aim of this paper is to show, via a simple but typical example, how such proofs can be constructed and checked using HOL—a mechanical theorem-proving system for higher-order logic. The secondary aim is to demonstrate a method for reasoning about distributed algorithms based on the notions of events and causality. The goal is to perform as much reasoning as possible in the events-and-causality view and then translate the results back to the processors-and-messages view, since the former is more abstract and easier to reason about than the latter. The example we use to illustrate our ideas is the verification of a simple distributed summation algorithm for trees. A companion paper [6] describes the formal graph theory needed for this task.
14766680
QoS Driven Parallelization of Resources to Reduce File Download Delay
In this paper, we propose a novel approach for reducing the download time of large files over the Internet. Our approach, known as parallelized file transport protocol (P-FTP), proposes simultaneous downloads of disjoint file portions from multiple file servers. P-FTP server selects file servers for the requesting client on the basis of a variety of QoS parameters, such as available bandwidth and server utilization. The sensitivity analysis of our file server selection technique shows that it performs significantly better than random selection. During the file transfer, P-FTP client monitors the file transfer flows to detect slow servers and congested links and adjusts the file distributions accordingly. P-FTP is evaluated with simulations and real-world implementation. The results show at least 50 percent reduction in download time when compared to the traditional file-transfer approach. Moreover, we have also carried out a simulation-based study to investigate the issues related to large scale deployment of our approach on the Internet. Our results demonstrate that a large number of P-FTP users has no adverse effect on the performance perceived by non-P-FTP users. In addition, the file servers and network are not significantly affected by large scale deployment of P-FTP
38950443
Mechanical Verification of Distributed Algorithms in Higher-Order Logic
The only practical way to verify the correctness of distributed algorithms with a high degree of confidence is to construct machine-checked, formal correctness proofs. In this paper we explain how to do so using HOL an interactive proof assistant for higher order logic developed by Gordon and others. First, we describ how to build an infrastructure in HOL that supports reasoning about distributed algorithms,including formal theories of predicates, temporal logic, labeled transitions systems, simulation of programs, translation of properties, and graphs. Then we demonstrate, via an exemple, how to use the powerful intuition about eventsand causality to guide and structure correctness proofs of distributed algorithms. The example used is the verification of PIF (propagation of information with feedback), which is a simple but typical distributed algorithm due to Segall.