EW 7最新文献

{"title":"Structured virtual synchrony: exploring the bounds of virtual synchronous group communication","authors":"Katherine Guo, W. Vogels, R. V. Renesse","doi":"10.1145/504450.504488","DOIUrl":"https://doi.org/10.1145/504450.504488","url":null,"abstract":"Multipoint communication protocols that offer group membership and virtually synchronous message delivery are commonly believed to be heavyweight and non-scalable. To meet the needs of large-scale computer-supported collaborative work, distributed parallel computing, and future worldwide applications, we designed the Structured Virtual Synchrony (SVS) protocol. The protocol has been implemented as part of Horus, a group communication system developed at Cornell University. It scales up to 800 members, while achieving a one-way latency of 100 milliseconds over groups of 500 members.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121313795","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Migrants: self-moving object clusters","authors":"E. Jul","doi":"10.1145/504450.504494","DOIUrl":"https://doi.org/10.1145/504450.504494","url":null,"abstract":"In a world connected by an Information Superhighway there will be many smaller highways, roads, and even paths to users. Users will roam around and touch upon the access paths at many different point with varying path bandwidths. Upon each access, the user will expect to see data, objects, and computations essential to his or her needs.\u0000We propose to provide such access using Migrant which, in a nutshell (excuse the pun), encapsulates small units of data, objects, and computation. The central idea behind migrants is that of carving out a subset of objects in an object based system where the subset represents some small part of one (or more) applications and letting this subject, called a migrant chase down the user wherever the user accesses the WorldWide net.\u0000A migrant can be considered a small agent containing essential data (and computations) which furthermore are aware of the network and are willing to travel as to find the user. For example, a simple migrant could contain a mail message plus information on where the migrant might rendez-vous with the user. On the way, the migrant may decide to replicate itself, so as to better show up wherever the user connects to the network next.\u0000Migrants must be application defined because they need to contain a suitable summary of some subset of the application. The application programmer defines distilling functions as to create migrants. The idea is that migrants are mini-replicas and are themselves replicable---an ability which is useful when trying to chase down the users. For example, a migrant may replicate itself by being sent to multiple plausible locations of the user.\u0000Migrants can also produce migrants of their own, e.g., a mail message migrant can produce a smaller migrant (max. 160 characters) that can be transmitted via the Short Message Service (SMS) of the GSM cellular system.\u0000Migrants can also be created at the user end, e.g., a user can create a migrant using a cellular phone by sending a SMS message. Upon receipt the migrant expands itself into a 257 real task, e.g., sending a real mail message, accessing a database, requesting the creation of a file migrant (e.g., to order retrieval of a file), etc.\u0000At the implementation level, migrants can be considered a form of active messages in that they contain the necessary code to identify and hook up with the application or user (or other migrant) that they are looking for. The underlying support layer is to provide transportation, location information, and location hints that the migrant can use in chasing down its destination. Thus the underlying transport layer must make parts of its information available to migrants. In many cases, a hunting migrants will not have to do much chasing because the underlying system has up-to-date location information and network connections to the destination. However, by exposing location information, migrants can then apply their own policy concerning the chasing to be done. This can include the further rep","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"21 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116989788","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Mobile host tracking and resource discovery","authors":"A. Baggio, Ian Piumarta","doi":"10.1145/504450.504481","DOIUrl":"https://doi.org/10.1145/504450.504481","url":null,"abstract":"In mobile environments, as computers move to unknown networks, they need to discover new services, applications, and other network resources. Since the performance characteristics of such environments are often poor (due mainly to wireless communications and the restricted power of machines), mobile hosts require access to the nearest equivalent of some resource. On the other hand, services and applications located on the fixed part of the network may need to be aware of mobile host locations, in order to redirect messages, replies, references, files, displays, and so on. To achieve such resource discovery and mobile host tracking, a possible solution is to use a mechanism that supports remote object references --- Stub-Scion Pair Chains --- extended to allow host movement, disconnection and reconnection. Given this mechanism, we are able to install on both the fixed and mobile parts of the network some dedicated objects that allow the management of resource accesses and locations of mobile hosts, via tables and chains of references.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"2 4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116797650","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"ParaWeb: towards world-wide supercomputing","authors":"Tim Brecht, H. Sandhu, Meijuan Shan, Jimmy Talbot","doi":"10.1145/504450.504484","DOIUrl":"https://doi.org/10.1145/504450.504484","url":null,"abstract":"In this paper, we describe the design of a system, called ParaWeb, for utilizing Internet or intra-net computing resources in a seamless fashion. The goal is to allow users to execute serial programs on faster compute servers or parallel programs on a variety of possibly heterogeneous hosts. ParaWeb provides extensions to the Java programming environment (through a parallel class library) and the Java runtime system that allow programmers to develop new Java applications with parallelism in mind, or to execute existing Java applications written using Java's multithreading facilities in parallel. Some experimental results from our prototype implementation are used to demonstrate the potential of this approach.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"23 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133981562","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cryptographic support for fault-tolerant distributed computing","authors":"Y. Minsky, R. V. Renesse, F. Schneider, S. Stoller","doi":"10.1145/504450.504472","DOIUrl":"https://doi.org/10.1145/504450.504472","url":null,"abstract":"Mobile processes, or agents, have been proposed for a variety of applications in the Internet and other large distributed systems. But little work has been directed at operating-system support for agents. This paper discusses one aspect of the problem---implementing fault-tolerance without specialized hardware.In traditional client-server settings, a central and trusted host may send all messages and receive all replies, thereby implementing a star-shaped communications pattern. In contrast, an agent can execute autonomously at a succession of remote sites without returning to the host that launched it. Thus, computations structured using agents may consume less network-bandwidth in performing tasks that involve multiple hosts. Moreover, for some settings, it is unrealistic to presume the existence of a central host that remains connected to the network---mobile computing and wireless networks are obvious examples.In an open distributed system, agents comprising an application must not only survive (possibly malicious) failures of the hosts they visit, but they must also be resilient to the potentially hostile actions of other hosts. Correctness of a computation should depend only on hosts that would be visited in a failure-free run. We assume that faulty hosts produce erroneous messages, that they can masquerade as other faulty hosts, but that they cannot assume the identities and do not have access to secrets of non-faulty hosts.Replication and voting are necessary to survive malicious behavior by visited hosts. However, faulty hosts that are not visited by agents can confound a naive replica-management scheme by spoofing. With this in mind, we have been investigating protocols for replication and voting in a family of applications. Our protocols use cryptographic techniques in novel ways. Furthermore, our experiments reveal that fast (correct) hosts can mask delays caused by slow ones, so replication actually speeds up some applications.Section 2 characterizes the family of applications treated in this paper. Section 3 describes experiments we ran to explore performance implications of replication and voting in this setting. The role of cryptographic techniques in our protocols is discussed in section 4. Section 5 contains our conclusions.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"19 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134369988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"System support for mobility","authors":"A. Black, Jon Inouye","doi":"10.1145/504450.504476","DOIUrl":"https://doi.org/10.1145/504450.504476","url":null,"abstract":"As we move closer to world-wide networking and the merger of computing and communications, truly mobile computing---computing while on the move---will become as unexceptional as truly mobile communication (using cellular telephones) is today. However, mobile computing poses new challenges for both system and application designers. Unlike telephony, where a new communications and terminal infrastructure was created to provide a well-understood service (peer-to-peer voice communication), and inter-operability was maintained at the central office, to realize the vision of mobile computing we need to adapt existing applications, and inter-operability must be provided for between peer applications and systems.Almost all of the computer applications that have been built to date make the assumption that their environment is invariant over a significant period of time. Previous generations of bespoke applications were designed around assumptions of computer speed, memory, network bandwidth, communications latency and user interface; changes in these assumptions may have necessitated a new design. Current mass-market (\"shrink-wrapped\") applications more commonly interrogate their environment when they are initialized, but then assume that nothing changes until after they terminate. Even a modest dynamic change, such as reducing the bit-depth of the available display (as might occur when a laptop is unplugged from a stationary monitor), is more than many applications can handle. Similarly, while operating systems are now often built to ascertain at boot time which network devices are available, and to initialize the appropriate drivers, they are typically unable to handle dynamic changes in these same attributes.The challenge of mobile computing is that many attributes of the application environment vary as the computer is moved from place to place. Moreover, the degree of variability is enormous. For example, available network bandwidth may vary by five orders of magnitude. Adapting to this variability is the shared responsibility of the application program and the operating system. We do not believe that there is a \"silver bullet\" that will automatically make all applications mobile. But we do believe that the use of the Synthetix specialization methodology will both make the problem tractable and will provide a framework for dividing between the application and the system the responsibility for adapting to change.The remainder of this position paper will describe in more detail the kind of variability that mobile applications will often encounter, and will then outline how we envisage adapting applications and systems to accommodate it.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"126 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122073037","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Techniques for handling scale and distribution in virtual worlds","authors":"K. O'Connell, T. Dinneen, S. Collins, B. Tangney, N. Harris, V. Cahill","doi":"10.1145/504450.504454","DOIUrl":"https://doi.org/10.1145/504450.504454","url":null,"abstract":"Lack of bandwidth and network latency are known to be major impediments to achieving realism in distributed virtual world (vw) applications with a large number of, potentially geographically dispersed, entities. This paper describes a combination of techniques that we are using to overcome these twin problems. The techniques described are intended to reduce both the volume and frequency of communication between the entities that make up the virtual world and include the use of anonymous event-based communication with notify constraints, scoping of event propagation with zones, and use of predictive approaches to replica management. Each of these techniques is described in turn.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"60 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130218835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A framework to support large-scale active applications","authors":"J. Bates","doi":"10.1145/504450.504452","DOIUrl":"https://doi.org/10.1145/504450.504452","url":null,"abstract":"Many applications are emerging which share the characteristic of being active, i.e. driven by asynchronous run-time events. The application areas include multimedia, cooperative working (such as conferencing), intelligent agent architectures, active database and support for user mobility. Prototype active applications are often developed from scratch as monolithic entities and are thus inflexible. Platforms which offer generalized support only usually deal with one application class in isolation.The thesis of this work is that active applications have generic requirements of a supporting platform. Rather than building each application as a monolithic entity, they can be composed of inter-connected sub-components called active objects. These objects can be used interchangeably in a plug-and-play architecture. This encourages on-the-fly application development and assists fast prototyping.This paper is supported by our implementation of a prototype distributed active application support platform. Our software is used to provide examples throughout. Section 1 describes the application requirements which a platform must be able to support. Section 2 describes the model for composing applications. Section 3 describes how a distributed programming platform has been enhanced for run-time object support and to allow new active object classes to be constructed easily. Finally, section 4 concludes.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130353769","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Wide-area information access to multimedia historical sources","authors":"Tim Mills, K. Moody","doi":"10.1145/504450.504462","DOIUrl":"https://doi.org/10.1145/504450.504462","url":null,"abstract":"An object-oriented model has been developed for heterogeneous multimedia data; this model underlies Cobra, a content-based retrieval architecture, which allows quick construction of powerful tools for wide area information access. The system is to be evaluated through case studies, the first of which is a search engine for historical records.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"94 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"117113681","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Bayou: replicated database services for world-wide applications","authors":"K. Petersen, M. Spreitzer, D. Terry, M. Theimer","doi":"10.1145/504450.504497","DOIUrl":"https://doi.org/10.1145/504450.504497","url":null,"abstract":"The Bayou architecture provides scalability, availability, extensibility, and adaptability features that address database storage needs of world-wide applications. In addition to discussing these features, this paper presents Bayou's mechanisms for permitting the replicas of a database to vary dynamically without global coordination. Key is the use of weak consistency replication among autonomous machines and strict adherence to the tenet that no operation should involve more than two machines.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"138 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"1996-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115404039","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}