10832557
Adaptive group scheduling mechanism using mobile agents in peer-to-peer grid computing environment
Peer-to-peer grid computing is an attractive computing paradigm for high throughput applications. However, both volatility due to the autonomy of volunteers (i.e., resource providers) and the heterogeneous properties of volunteers are challenging problems in the scheduling procedure. Therefore, it is necessary to develop a scheduling mechanism that adapts to a dynamic peer-to-peer grid computing environment. In this paper, we propose a Mobile Agent based Adaptive Group Scheduling Mechanism (MAAGSM). The MAAGSM classifies and constructs volunteer groups to perform a scheduling mechanism according to the properties of volunteers such as volunteer autonomy failures, volunteer availability, and volunteering service time. In addition, the MAAGSM exploits a mobile agent technology to adaptively conduct various scheduling, fault tolerance, and replication algorithms suitable for each volunteer group. Furthermore, we demonstrate that the MAAGSM improves performance by evaluating the scheduling mechanism in Korea@Home.
16177959
Multi-Node Global Directory Construction in Peer-to-Peer Systems
In P2P systems, the speed of searching for desired lists of sharable files is one of the most important measurement issues in evaluation of overall system performance. Although the searching schemes of existing non-structured P2P systems have been improved to enhance speed considerably, they still never reach to the level of those of the centralized and structured systems. In this paper, we propose a multi-node global directory in P2P systems, where all the lists of sharable resources of the joining peers are aggregated and divided into the chosen nodes while keeping collating sequence as a whole to make one big linked list. Thus in indexed sequential searching, the system provides us with convenience of using the command like 'dir' of MS-DOS, and in general keyword searching, which is naturally impossible for the structured P2P systems, the searching speed is even faster than those of centralized P2P systems since a small list segment is scanned at each node synchronously in parallel
24012185
Dynamic Scheduling Mechanism for Result Certification in Peer to Peer Grid Computing
In a peer to peer grid computing environment, volunteers have heterogeneous properties and dynamically join and leave during execution. Therefore, it is essential to adapt to an unstable and widely distributed environment. However, existing scheduling and result certification mechanisms do not adapt to such a dynamic environment. As a result, they undergo high overhead, performance degradation, and scalability problems. 
 
To solve the problems, we propose a new scheduling mechanism for result certification. The proposed mechanism applies different scheduling and result certification algorithms to different volunteer groups that are classified on the basis of their properties such as volunteering service time, availability, and credibility. It also exploits mobile agents in a distributed way in order to adapt to a dynamic peer to peer grid computing environment.
14154834
Region-based stage construction protocol for fault tolerant execution of mobile agent
Fault tolerance is essential to the development of reliable mobile agent systems in order to guarantee continuous execution of mobile agents. For this purpose, previous work has proposed fault tolerant protocols for mobile agent execution based on stage construction. However, when previous protocols are applied to a multiregion mobile agent computing environment, the overhead of work such as monitoring, election, voting and agreement is increased. We propose a region-based stage construction (RBSC) protocol for fault tolerant execution of mobile agents in a multiregion mobile agent computing environment. The RBSC protocol uses new concepts of quasiparticipant and substage in order to put together some places located in different regions within a stage in the same region. Therefore, the RBSC protocol decreases the overhead of stage works. Consequently, the RBSC protocol decreases the total execution time of mobile agents.
1688268
Mobile Agent Based Adaptive Scheduling Mechanism in Peer to Peer Grid Computing
In a peer to peer grid computing environment, volunteers are exposed to failures such as crash and link failures. In addition, since volunteers can dynamically join and leave executions and they are not dedicated only to a peer to peer grid computing, the executions of volunteers are stopped or suspended more frequently than in a grid computing environment. These failures result in the delay and blocking of the executions of tasks and even partial or entire loss of the executions. In addition, these failures make it difficult for a volunteer server to schedule tasks and manage the allocated tasks as well as volunteers. Existing peer to peer grid computing systems, however, do not deal with these failures in scheduling mechanisms. Moreover, since existing scheduling mechanisms are performed only by a volunteer server in a centralized way, there is a high overhead. 
 
To solve these problems, we propose a mobile agent based adaptive scheduling mechanism (MAASM). We implemented MAASM in Korea@Home and ODDUGI mobile agent system. The MAASM reduces the overhead of volunteer server by using mobile agents in scheduling procedure in a distributed way. In addition, it tolerates the various failures(especially, volunteer autonomy failures) which frequently occur in a peer to peer grid computing environment. Consequently, MAASM guarantees reliable and continuous executions in spite of the failures, so it decreases total execution time.
41968338
Group-Based Scheduling Scheme for Result Checking in Global Computing Systems
This paper considers the problem of correctness to fault-tolerance in global computing systems. Global computing system has been shown to be exposed to intentional attacks, where authentication is not relevant, network security techniques are insufficient. To guarantee correctness for computation, fault-tolerance schemes have been used to majority voting and spot-checking but these schemes intend to high computation delay because are not applied scheduling scheme for result checking. In this paper, we propose a new technique called GBSS(Group-Based Scheduling Scheme) which guarantee correctness and reduce computation delay by using fault-tolerant scheduling scheme to the result checking. Additionally, simulation results show increased usable rate of the CPU and increased performance of the system.
6394953
Accelerating Database Processing at e-Commerce Sites
Most e-commerce Web sites dynamically generate their contents through a three-tier server architecture composed of a Web server, an application server, and a database server. In such an architecture, the database server easily becomes a bottleneck to the overall performance. In this paper, we propose WDBAccel, a high-performance database server accelerator that significantly improves the throughput of the database processing, and thus that of the overall Web site. WDBAccel eliminates costly, complex query processing needed to obtain query results by reusing previous query results for subsequent queries. This differentiates WDBAccel from other database cache systems, which replicate a database into multiple conventional DBMS’s and distribute queries among them. We evaluate the performance of WDBAccel by using the queries of the TPC-W benchmark. The measurement results show that WDBAccel outperforms DBMS-based cache systems by up to an order of magnitude.
46451597
The RETOS operating system: kernel, tools and applications
19983253
A selective DVS technique based on battery residual
Abstract Conventional research on DVS assumes that the battery, which is the power source of most mobile devices, provides constant power; the battery, however, has unique discharge characteristics due to its chemical properties. Based on the residual characteristics of the battery, this paper presents a practical approach towards a battery-aware DVS mechanism that can easily be applied to conventional operating systems. The proposed policy monitors the battery residual in runtime, classifies the current battery state as one of three—the recovery effect region, the rate capacity region and the alarm region—then applies a suitable DVS algorithm according to each region, which takes advantage of the underlying battery characteristics. Experiments on commercial PDAs (iPAQ5550 and Zaurus SL-860 PDA) running MPEG applications showed that our policy significantly extends the battery lifetime, compared to the conventional DVS method, with only a marginal QoS degradation.
7326399
A Scalable Update Management Mechanism for Query Result Caching Systems at Database-Driven Web Sites
A key problem in using caching technology for dynamic contents lies in update management. An update management scheme should be very efficient without imposing much extra burden to the system, especially to the original database server. We propose an scalable update management mechanism for query result caching in database-backed Web sites. Our mechanism employs a two-phase consistency checking method, which prunes out unaffected queries at the earliest possible moment. The method scales well with a high number of cached instances.
15388195
Dynamically Weighted Hidden Markov Model for Spam Deobfuscation
Spam deobfuscation is a processing to detect obfuscated words appeared in spam emails and to convert them back to the original words for correct recognition. Lexicon tree hidden Markov model (LTHMM) was recently shown to be useful in spam deobfuscation. However, LT-HMM suffers from a huge number of states, which is not desirable for practical applications. In this paper we present a complexity-reduced HMM, referred to as dynamically weighted HMM (DW-HMM) where the states involving the same emission probability are grouped into super-states, while preserving state transition probabilities of the original HMM. DWHMM dramatically reduces the number of states and its state transition probabilities are determined in the decoding phase. We illustrate how we convert a LT-HMM to its associated DW-HMM. We confirm the useful behavior of DW-HMM in the task of spam deobfuscation, showing that it significantly reduces the number of states while maintaining the high accuracy.