Issues in providing a reliable multicast facility

Issues involved in point-to-multipoint communication are presented and the literature for proposed solutions and approaches surveyed. Particular attention is focused on the ideas and implementations that align with the requirements of the environment of interest. The attributes of multicast receiver groups that might lead to useful classifications, what the functionality of a management scheme should be, and how the group management module can be implemented are examined. The services that multicasting facilities can offer are presented, followed by mechanisms within the communications protocol that implements these services. The metrics of interest when evaluating a reliable multicast facility are identified and applied to four transport layer protocols that incorporate reliable multicast

An Approach for Supporting Ad-hoc Modifications in Distributed Workflow Management Systems

Supporting enterprise-wide or even cross-organizational business processes is a characteristic challenge for any workflow management system (WfMS). Scalability at the presence of high loads as well as the capability to dynamically modify running workflow (WF) instances (e.g., to cope with exceptional situations) are essential requirements in this context. Should the latter one, in particular, not be met, the WfMS will not have the necessary flexibility to cover the wide range of process-oriented applications deployed in many organizations. Scalability and flexibility have, for the most part, been treated separately in the relevant literature thus far. Even though they are basic needs for a WfMS, the requirements related with them are totally different. To achieve satisfactory scalability, on the one hand, the system needs to be designed such that a workflow instance can be controlled by several WF servers that are as independent from each other as possible. Yet dynamic WF modifications, on the other hand, necessitate a (logical) central control instance which knows the current and global state of a WF instance. For the first time, this paper presents methods which allow ad-hoc modifications (e.g., to insert, delete, or shift steps) to be performed in a distributed WfMS; i.e., in a WfMS with partitioned WF execution graphs and distributed WF control. It is especially noteworthy that the system succeeds in realizing the full functionality as given in the central case while, at the same time, achieving extremely favorable behavior with respect to communication costs

Fleets: Scalable Services in a Factored Operating System

Current monolithic operating systems are designed for uniprocessor systems, and their architecture reflects this. The rise of multicore and cloud computing is drastically changing the tradeoffs in operating system design. The culture of scarce computational resources is being replaced with one of abundant cores, where spatial layout of processes supplants time multiplexing as the primary scheduling concern. Efforts to parallelize monolithic kernels have been difficult and only marginally successful, and new approaches are needed. This paper presents fleets, a novel way of constructing scalable OS services. With fleets, traditional OS services are factored out of the kernel and moved into user space, where they are further parallelized into a distributed set of concurrent, message-passing servers. We evaluate fleets within fos, a new factored operating system designed from the ground up with scalability as the first-order design constraint. This paper details the main design principles of fleets, and how the system architecture of fos enables their construction. We describe the design and implementation of three critical fleets (network stack, page allocation, and file system) and compare with Linux. These comparisons show that fos achieves superior performance and has better scalability than Linux for large multicores; at 32 cores, fos's page allocator performs 4.5 times better than Linux, and fos's network stack performs 2.5 times better. Additionally, we demonstrate how fleets can adapt to changing resource demand, and the importance of spatial scheduling for good performance in multicores

SocialLink: a Social Network Based Trust System for P2P File Sharing Systems

In peer-to-peer (P2P) file sharing systems, many autonomous peers without preexisting trust relationships share files with each other. Due to their open environment and distributed structure, these systems are vulnerable to the significant impact from selfish and misbehaving nodes. Free-riding, whitewash, collusion and Sybil attacks are common and serious threats, which severely harm non-malicious users and degrade the system performance. Many trust systems were proposed for P2P file sharing systems to encourage cooperative behaviors and punish non-cooperative behaviors. However, querying reputation values usually generates latency and overhead for every user. To address this problem, a social network based trust system (i.e., SocialTrust) was proposed that enables nodes to first request files from friends without reputation value querying since social friends are trustable, and then use trust systems upon friend querying failure when a node\u27s friends do not have its queried file. However, trust systems and SocialTrust cannot effectively deal with free-riding, whitewash, collusion and Sybil attacks. To handle these problems, in this thesis, we introduce a novel trust system, called SocialLink, for P2P file sharing systems. By enabling nodes to maintain personal social network with trustworthy friends, SocialLink encourages nodes to directly share files between friends without querying reputations and hence reduces reputation querying cost. To guarantee the quality of service (QoS) of file provisions from non-friends, SocialLink establishes directionally weighted links from the server to the client with successful file transaction history to constitute a weighted transaction network , in which the link weight is the size of the transferred file. In this way, SocialLink prevents potential fraudulent transactions (i.e., low-QoS file provision) and encourages nodes to contribute files to non-friends. By constraining the connections between malicious nodes and non-malicious nodes in the weighted transaction network, SocialLink mitigates the adverse effect from whitewash, collusion and Sybil attacks. By simulating experiments, we demonstrate that SocialLink efficiently saves querying cost, reduces free-riding, and prevents damage from whitewash, collusion and Sybil attacks

Client server computing and cooperative processing

https://egrove.olemiss.edu/aicpa_guides/1387/thumbnail.jp