EW 7最新文献

{"title":"Supporting broad internet access to TACOMA","authors":"D. Johansen, R. V. Renesse, F. Schneider","doi":"10.1145/504450.504461","DOIUrl":"https://doi.org/10.1145/504450.504461","url":null,"abstract":"The TACOMA system [JRS95] provides operating-system support for mobile processes, or agents, that traverse the hosts of a network in accomplishing some task. A TACOMA agent executing on one host moves to another host by using TCP to communicate with TACOMA software at the destination host. The presumption is that TACOMA software has been installed at any host that might launch or be visited by an agent. This presumption is questionable:• System managers are reluctant to install software that allows arbitrary imported software, like agents, to be executed on their hosts. And, there is good reason for this reluctance.• Hosts are autonomous. So, even were security not a concern, arranging for installation of a piece of non-critical software on a significant fraction of the hosts in a large network is impractical.The network-software installation-problem is not unique to agents or to TACOMA. Any provider of software will be faced with this problem if that software must be installed on autonomous sites of a large network. The speed with which WWW software spread through the Internet was an exception; architects of distributed-application support-software should not plan on having their systems disseminated in such a fashion. But, these architects better have some plan for disseminating their systems, since the utility and success of large networks will depend on offering new services in a timely way.This paper reports experiences in addressing the network-software installation-problem for TACOMA. However, we believe that the techniques employed have utility in other situations as well. The next section gives an overview of TACOMA and the applications it currently supports. Section 3 describes a WWW-based scheme for avoiding software installation at all sites that might launch TACOMA agents; section 4 discusses an email-based scheme. Section 5 concludes with a summary and some observations.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"3 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":"125383415","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":"Towards a world-wide civilization of objects","authors":"Michael Condict, D. Milojicic, F. Reynolds, D. Bolinger","doi":"10.1145/504450.504456","DOIUrl":"https://doi.org/10.1145/504450.504456","url":null,"abstract":"The Internet today corresponds to a Feudal society, where fortress walls (firewalls) surround villages (LANs), little pockets of civilization connected by lawless highways (insecure networks) infested by bandits (hackers). The emergence of the World Wide Web and Java have shown the way towards a true civilization of electronic objects, although it does not yet exist. To assist in its evolution, we propose to extend the World Wide Web and Java with object-oriented, distributed OS services, implemented in Java. The goal is to make it commonplace for applications and objects to be distributed across unrelated sites and for mobile objects and agents to travel and trade freely around the world. We describe some problems such a system faces, such as in the areas of security and performance, and give a high-level design that addresses them.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"203 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":"132080852","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 flexible hybrid concurrency control model for collaborative applications in large scale settings","authors":"G. Pierre, Clive K. Liu","doi":"10.1145/504450.504498","DOIUrl":"https://doi.org/10.1145/504450.504498","url":null,"abstract":"Large-scale collaborative applications are difficult to build because of their high concurrency control needs and the heterogeneity of the underlying architecture. Due to these difficulties, only a few large-scale applications have been developed, such as Usenet or irc. To facilitate the realisation of such applications, we propose a more precise definition of the application's needs, in order to provide a good \"quality\" of cooperation when it is needed, and cheaper cooperation when it is acceptable. The model of LaSCoW (Large Scale Collaborative Work) allows the applications to be partitioned into separate consistency domains, each domain implementing its own collaboration policy.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"58 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":"133415675","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":"AFS and the web: competitors or collaborators?","authors":"M. Satyanarayanan, M. Spasojevic","doi":"10.1145/504450.504468","DOIUrl":"https://doi.org/10.1145/504450.504468","url":null,"abstract":"Over the last few years, the World-Wide Web [2] has risen to dominance as a mechanism for wide-area information access. Each day brings new reports of the growth of the Web, and this trend shows no signs of abating any time soon. To many people, the Web and the Internet are synonymous. Unfortunately, success has exposed many limitations of the Web such as its tendency to overload the network and servers, its limited ability to control access to sensitive data, its lack of mechanisms for data consistency, and its susceptibility to network and server failures. It is now widely recognized that these problems must be solved for the continued growth of the Web.With much less fanfare, another world-wide information system, AFS, has also been operational on the Internet. AFS was originally designed to support the file sharing needs of a campus-sized community of five to seven thousand workstations [11, 15]. In current parlance, AFS was conceived as an information sharing mechanism for the Intranet of an organization. Since then, AFS has been evolved to function effectively over the Internet [17, 21]. Many organizations have been part of a single distributed Unix file name space supported by AFS. As of 1994, this system spanned well over 100 organizations world-wide, with each organization typically containing many tens or hundreds of clients. Measurements reported in a recent paper [20] confirm that AFS does indeed function effectively at this scale.The goal of this paper is to critically compare these two mechanisms for world-wide information access. We begin by asking the following questions: What are the relative strengths and weaknesses of the two mechanisms? Which of these differences are superficial, and which are deep? Why is the Web so much more visible and popular?In performing this comparison, it is important to keep in mind that the two mechanisms are not addressing precisely the same problem. While AFS has the relatively narrow and well-defined goal of provided distributed Unix file access, the goal of the Web is broader and less explicit. Further, AFS is now stable and mature while many aspects of the Web are still evolving. In spite of these caveats, we believe that a comparison of the two mechanisms will provide useful insights.Our comparison shows that the Web and AFS are not really competing technologies. Rather, they represent complementary technologies that may be used together for mutual advantage. We present real-life examples to confirm that this potential can indeed be realized in practice.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"58 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":"126810293","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":"Adding realtime applets and quality of service support to the world wide web","authors":"K. Lakshman, M. Manoharan, R. Yavatkar","doi":"10.1145/504450.504495","DOIUrl":"https://doi.org/10.1145/504450.504495","url":null,"abstract":"Predictable Quality Of Service (QoS) in terms of controlled response time and guaranteed bandwidth is increasingly important in World Wide Web. We propose a variety of enhancements and extensions to the existing Web infrastructure so that Web applications and applets can provide predictable quality of service. The proposed extensions include addition of the notion of QoS to the HTML/HTTP/Java syntax, QoS negotiation and adaptation mechanisms in Java classes and threads, QoS reservation support at the socket and transport protocol layers, and ATM signaling extensions for dynamic QoS re-negotiation over persistent HTTP connections. Our ongoing work includes implementation of these extensions and an evaluation over a testbed consisting of a network of Unix workstations and ATM switches.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"47 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":"127213434","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":"Using events to build large scale distributed applications","authors":"R. Hayton, J. Bacon, J. Bates, K. Moody","doi":"10.1145/504450.504453","DOIUrl":"https://doi.org/10.1145/504450.504453","url":null,"abstract":"We have extended an Interface Definition Language to handle event registration and notification. Clients register interest in specified classes of events, and servers then notify them of any occurrence asynchronously. Event occurrences are identified by parameters which conform to IDL typing constraints and can therefore be used in synchronous method invocations. Methods to handle registration and notification are generic and can be inherited by objects of any class: as a by-product of IDL processing the stubs to handle event creation and decoding are generated automatically. We have implemented a prototype composite event recogniser based on nested finite state machines and have defined an event algebra and language to specify composite events.The approach is inherently scalable in that only events in which an interest has been registered are notified. Alternative approaches lead to polling, mining for event data or being flooded with superfluous events.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"12 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":"133398995","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 multicast-based distributed file system for the internet","authors":"B. Grönvall, I. Marsh, S. Pink","doi":"10.1145/504450.504469","DOIUrl":"https://doi.org/10.1145/504450.504469","url":null,"abstract":"JetFile is a file system designed with multicast as its distribution mechanism. The goal is to support a large number of clients in an environment such as the Internet where hosts are attached to both high and low speed networks, sometimes over long distances. JetFile is designed for reduced reliance on servers by allowing client-to-client updates using scalable reliable multicast. Clients on high speed networks prefetch large numbers of files. On low speed networks such as wireless, special caching policies are used to decrease file access latency. The prototype implementation of JetFile is on the JetStream gigabit local area network which provides hardware support for many multicast addresses. The multicast Internet backbone (Mbone) is the wide area testbed for JetFile.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"16 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":"127574847","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":"Scalable information sharing in large scale distributed systems","authors":"M. Ahamad, S. Bhola, R. Kordale, F. Torres-Rojas","doi":"10.1145/504450.504480","DOIUrl":"https://doi.org/10.1145/504450.504480","url":null,"abstract":"Many application domains have already demonstrated that they can benefit greatly if efficient access can be provided to shared information across widely distributed users. We use the generic term object to describe units of shared information which could include files, web pages or language defined objects. Future applications will require object sharing modes richer than simple browsing. For example, a collaboration system that allows users distributed world-wide (e.g., managers of a multinational company) to interact with each other must manipulate objects that are both read and updated at multiple locations.Several assumptions, which are natural in the context of large scale systems, can be made about scalable object sharing systems. First, such systems will consist of many server nodes that will act as the storehouses for shared objects. These servers will enable access to objects to a much larger number of client nodes. To avoid high latencies and communication costs, servers will store replicated copies of objects frequently accessed by clients in their vicinity. Furthermore, clients will cache objects to reduce access latency and frequency of communication with servers. Both replication at servers and caching at clients result in multiple copies of an object which introduces the problem of maintaining consistency among the copies.Many levels of consistency are possible and the choice of a particular consistency level has implications on the programming as well as performance of a distributed application. Although consistency requirements across copies of a single object are easily seen, such requirements can arise between copies of different but related objects. For example, assume that user 1 writes a memo object ol to produce version o1,1 and later generates its updated version ol,2. User 2 reads ol,2 and writes memo object o2 in response. If user 3 reads memo o2 and wants to read o1 to understand it, it must be provided ol,2 and not o1,1 which could have been cached by it due to a previous read. Thus, consistency requirements exist across copies of ol and o2 even when user 3 accesses them in a read-only mode.We first identify some requirements that must be met by scalable object sharing schemes. We present arguments to demonstrate that existing techniques cannot easily be adapted to meet these requirements. This is followed by an outline of our approach.","PeriodicalId":137590,"journal":{"name":"EW 7","volume":"PP 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":"126405383","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}