物件導向軟體之架構(Object-Oriented Software Construction)探討

An apparatus for transmitting a file with enhanced transmission security through a network includes a file-splitting processor that splits the file into a plurality of message segments and addresses the plurality of message segments to a plurality of addresses assigned to a receiving host. The apparatus includes a message segment transmitter for transmitting the plurality of message segments to the receiving host.

Camouflage of network traffic to resist attack

The phenomenal growth in popularity of the World Wide Web (WWW, or the Web) has made WWW traffic the largest contributor to packet and byte traffic on the NSFNET backbone. This growth has triggered recent research aimed at reducing the volume of network traffic produced by Web clients and servers, by using caching, and reducing the latency for WWW users, by using improved protocols for Web interaction.Fundamental to the goal of improving WWW performance is an understanding of WWW workloads. This paper presents a workload characterization study for Internet Web servers. Six different data sets are used in this study: three from academic (i.e., university) environments, two from scientific research organizations, and one from a commercial Internet provider. These data sets represent three different orders of magnitude in server activity, and two different orders of magnitude in time duration, ranging from one week of activity to one year of activity.Throughout the study, emphasis is placed on finding workload invariants: observations that apply across all the data sets studied. Ten invariants are identified. These invariants are deemed important since they (potentially) represent universal truths for all Internet Web servers. The paper concludes with a discussion of caching and performance issues, using the invariants to suggest performance enhancements that seem most promising for Internet Web servers.

Web server workload characterization: the search for invariants

This paper discusses the design and performance of a hierarchical proxy-cache designed to make Internet information systems scale better. The design was motivated by our earlier trace-driven simulation study of Internet traffic. We challenge the conventional wisdom that the benefits of hierarchical file caching do not merit the costs, and believe the issue merits reconsideration in the Internet environment.

The cache implementation supports a highly concurrent stream of requests. We present performance measurements that show that our cache outperforms other popular Internet cache implementations by an order of magnitude under concurrent load. These measurements indicate that hierarchy does not measurably increase access latency. Our software can also be configured as a Web-server accelerator; we present data that our httpd-accelerator is ten times faster than Netscape's Netsite and NCSA 1.4 servers.

Finally, we relate our experience fitting the cache into the increasingly complex and operational world of Internet information systems, including issues related to security, transparency to cache-unaware clients, and the role of file systems in support of ubiquitous wide-area information systems.

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A hierarchical internet object cache

A client-server interactive television program guide system is provided. An interactive television program guide client is implemented on user television equipment. The interactive television program guide provides users with an opportunity to define expressions that are processed by the program guide server. The program guide server may provide program guide data, schedules reminders, schedules program recordings, and parentally locks programs based on the expressions. Users' viewing histories may be tracked. The program guide server may analyze the viewing histories and generates viewing recommendations, targets advertising, and collects program ratings information based on the viewing histories.

Client-server electronic program guide

A technique for automatic, transparent, distributed, scalable and robust caching, prefetching, and replication in a computer network that request messages for a particular document follow paths from the clients to a home server that form a routing graph. Client request messages are routed up the graph towards the home server as would normally occur in the absence of caching. However, cache servers are located along the route, and may intercept requests if they can be serviced. In order to be able to service requests in this manner without departing from standard network protocols, the cache server needs to be able to insert a packet filter into the router associated with it, and needs also to proxy for the homer server from the perspective of the client. Cache servers may cooperate to service client requests by caching and discarding documents based on its local load, the load on its neighboring caches, attached communication path load, and on document popularity. The cache servers can also implement security schemes and other document transformation features.

A method and system for distributed caching, prefetching and replication

Foreword. Preface. 1. Introduction. 2. Replication of Data. 3. Replication of Processes. 4. Replication of Objects. 5. Replication of Messages. 6. Replication in Heterogeneous, Mobile, and Large-Scale Systems. 7. The Future of Replication. A: Systems. B: Further Readings. C: Serializability Theory. References. Index.

Replication techniques in distributed systems

With the increasing demand for document transfer services such as the World Wide Web comes a need for better resource management to reduce the latency of documents in these systems. To address this need, we analyze the potential for document caching at the application level in document transfer services. We have collected traces of actual executions of Mosaic, reflecting over half a million user requests for WWW documents. Using those traces, we study the tradeoffs between caching at three levels in the system, and the potential for use of application-level information in the caching system. Our traces show that while a high hit rate in terms of URLs is achievable, a much lower hit rate is possible in terms of bytes, because most profitably-cached documents are small. We consider the performance of caching when applied at the level of individual user sessions, at the level of individual hosts, and at the level of a collection of hosts on a single LAN. We show that the performance gain achievable by caching at the session level (which is straightforward to implement) is nearly all of that achievable at the LAN level (where caching is more difficult to implement). However, when resource requirements are considered, LAN level caching becomes muck more desirable, since it can achieve a given level of caching performance using a much smaller amount of cache space. Finally, we consider the use of organizational boundary information as an example of the potential for use of application-level information in caching. Our results suggest that distinguishing between documents produced locally and those produced remotely can provide useful leverage in designing caching policies, because of differences in the potential for sharing these two document types among multiple users. >

Application-level document caching in the Internet

A technique fulfills service requests in a system of computers that communicate as nodes within a network. The technique involves sending, in response to an initial service request that requests a service provided by a primary server node, a mobile agent from the primary server node to an intermediate node. The mobile agent indicates to the intermediate node that a secondary server node is capable of providing the service. The technique further involves intercepting, at the intermediate node, a subsequent service request sent from a client node to the primary server node, the subsequent service request requesting the service, and sending an instruction from the intermediate node to the secondary server node. The instruction instructs the secondary server node to provide the service. The technique further includes providing, in response to the instruction, the service from the secondary server node to the client node.

Extending network services using mobile agents

A technique for automatic, transparent, distributed, scalable and robust replication of document copies in a computer network wherein request messages for a particular document follow paths from the clients to a home server that form a routing graph. Client request messages are routed up the graph towards the home server as would normally occur in the absence of caching. However, cache servers are located along the route, and may intercept requests if they can be serviced. In order to be able to service requests in this manner without departing from standard network protocols, the cache server needs to be able to insert a packet filter into the router associated with it, and needs also to proxy for the home server from the perspective of the client. Cache servers cooperate to update cache content by communicating with neighboring caches whenever information is received about invalid cache copies.

Abdelsalam A. Heddaya

Papers

A method and system for distributed caching, prefetching and replication

Replication techniques in distributed systems

Application-level document caching in the Internet

Extending network services using mobile agents

Protocol for distributing fresh content among networked cache servers