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IEEE International conference on Multimedia Computing and systems (ICMCS)

作者： K.L.E. Law B. Nandy A. Chapman Nortel Limited Ottawa Canada

With the wide-spread popularity of the World-Wide Web (WWW), network and server load increases dramatically. Caching proxies have been introduced to improve the system performance with the assumption that a page will be fetched many times before it is destroyed or modified. However the increase in user requests has driven up to the limit of the proxy performance. The authors present a distributed proxy server architecture that can increase the service availability, provide system scaleability, coupled with load balancing capability. The system employs TCP-based switching mechanism which has a finer session granularity, and more dynamic control on resource allocation.

关键词： World Wide Web Web server network servers Delay Bandwidth control systems internet Protocols IP networks System performance

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Analyzing stability in wide-area network performance

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performance Evaluation Review 1997年第1期25卷 2-12页

作者： Balakrishnan, Hari Stemm, Mark Seshan, Srinivasan Katz, Randy H. Univ of California at Berkeley Berkeley United States

The internet is a very large scale, complex, dynamical system that is hard to model and analyze. In this paper, we develop and analyze statistical models for the observed end-to-end network performance based on extensive packet-level traces (consisting of approximately 1.5 billion packets) collected from the primary Web site for the Atlanta Summer Olympic Games in 1996. We find that observed mean throughputs for these transfers measured over 60 million complete connections vary widely as a function of end-host location and time of day, confirming that the internet is characterized by a large degree of heterogeneity. Despite this heterogeneity, we find (using best-fit linear regression techniques) that we can express the throughput for Web transfers to most hosts as a random variable with a log-normal distribution. Then, using observed throughput as the control parameter, we attempt to quantify the spatial (statistical similarity across neighboring hosts) and temporal (persistence over time) stability of network performance. We find that internet hosts that are close to each other often have almost identically distributed probability distributions of throughput. We also find that throughputs to individual hosts often do not change appreciably for several minutes. Overall, these results indicate that there is promise in protocol mechanisms that cache and share network characteristics both within a single host and amongst nearby hosts.

关键词： Wide area networks

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Window-based error recovery and flow control with a slow acknowledgement channel: A study of TCP/IP performance

Window-based error recovery and flow control with a slow ack...

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Proceedings of the 1997 16th IEEE Annual conference on Computer Communications, INFOCOM. Part 1 (of 3)

作者： Lakshman, T.V. Madhow, U. Suter, Bernhard Lucent Technologies Holmdel United States

With the envisaged growth in internet access services over networks with asymmetric links such as Asymmetric Digital Subscriber Line (ADSL) and Hybrid Fiber Coax (HFC), it becomes crucial to evaluate the performance of window-based protocols over systems in which the reverse link is considerably slower than the forward link. Even if the actual bandwidth asymmetry is moderate, high effective asymmetries can result because of bidirectional traffic. Our objective is to determine, whether TCP/IP performs reasonably in a setting in which the reverse link is the primary bottleneck. Our main results are: (1) For both the prevalent Tahoe version with Fast Retransmit and the Reno version of TCP, we determine the throughput as a function of buffering, round-trip times and normalized asymmetry (taken to be the ratio of the transmission time of ACKs in the reverse path to that of data packets in the forward path). We identify three modes of operation which are dependent on the forward buffer sizes and the normalized asymmetry. (2) Asymmetry increases TCP's already high sensitivity to random packet losses that might be caused by transient bursts in real-time traffic. Specifically, random loss leads to significant throughput deterioration when the product of the loss probability, the asymmetry and the square of the bandwidth delay product is large. (3) Congestion in the reverse path adds considerably to TCP's unfairness when multiple connections share the reverse link. Link bandwidth sharing is unfair even for connections with identical round-trip times and hence use of per connection buffer allocation on the reverse path appears essential.

关键词： network protocols

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Dynamic congestion control and error recovery over a heterogeneous internet

Dynamic congestion control and error recovery over a heterog...

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IEEE conference on Decision and control

作者： U. Madhow Coordinated Science Laboratory and ECE Department University of Illinois Urbana IL USA

In the heterogeneous internet of the future, end-to-end transport protocols for error recovery and congestion control must be able to handle large bandwidth delay products, random loss (i.e., loss due to phenomena which occur on a time scale faster than the feedback delay), and possibly asymmetry between the bottleneck link capacities on the data and acknowledgement (ACK) paths. Our objective in this paper is to provide a flavor of transport protocol design and analysis in this scenario by illustrating two key points: (a) Although rigorous analysis for transport protocols over heterogeneous networks is difficult, approximate analysis can be used to obtain rules of thumb that are invaluable for designing network level controls for supporting transport protocols. This is illustrated by showing how our recently developed analytical understanding of TCP/IP, the popular internet transport protocol, leads to network control mechanisms for hiding the time variations and losses of a wireless link from TCP, or for dealing with the effect of asymmetry. (b) While it is not clear that the feedback structure required to apply traditional control schemes is available at the transport layer, application of systems level thinking in protocol design can lead to significant performance gains over TCP/IP. We illustrate this using our recent work on a transport protocol based on a novel ACK format that conveys information sufficient for error recovery and congestion control even with an ACK path of poor quality.

关键词： Error correction Transport protocols TCPIP control systems Delay effects Feedback internet Bandwidth Thumb Level control

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Domain and type enforcement firewalls

Domain and type enforcement firewalls

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Annual Computer Security Applications conference

作者： K.A. Oostendorp L. Badger C.D. Vance W.G. Morrison M.J. Petkac D.L. Sherman D.F. Sterne Trusted Inf. Syst. Inc. Glenwood MD USA Trusted Information Systems Inc. Glenwood MD USA

internet connected organizations often employ an internet firewall to mitigate risks of system penetration, data theft, data destruction, and other security breaches. Conventional internet firewalls, however, impose an overly simple inside vs outside model of security that is incompatible with many business practices that require extending limited trust to external entities. The paper reports on our experience with an enhanced security firewall based on Domain and Type Enforcement (DTE), a strong but flexible form of access control. A DTE firewall provides several benefits. First, it runs application level proxies in restrictive domains, thereby increasing security, and runs network services such as HTTP and FTP under DTE controls, thereby reducing risks that network based attacks will compromise local resources. Second, a DTE firewall coordinates role based security policies that span networks by passing DTE security attributes between DTE clients and servers. These attributes allow security policies at the endpoints to be coordinated; such coordination adds defense in depth to the traditional firewall security perimeter: this permits safe exportation of normally risky services such as NFS. Finally, a DTE firewall interoperates with "non DTE" systems and associates DTE security attributes with these systems so their interaction with DTE clients or servers can be controlled. We describe the design of a prototype DTE firewall system and informally evaluate its security, compatibility, functionality, and performance.

关键词： Data security internet Protection network servers Access control Tunneling Protocols Mobile agents Web server control systems

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Access control in wide-area networks

Access control in wide-area networks

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International conference on Distributed Computing systems

作者： M.A. Hiltunen R.D. Schlichting Department of Computer Science University of Arizona Tucson Tucson USA

Access control involves maintaining information about which users can access system resources and ensuring that access is restricted to authorized users. In wide-area networks such as the internet, implementing access control is difficult, since resources may be replicated, the task of managing access rights may be distributed among multiple sites, and events such as host failures, host recoveries, and network partitions must be dealt with. This paper explores the problem of access control in such an environment, and in particular the inherent tradeoff between security, availability, and performance. Techniques for dealing with access control in the presence of partitions are presented and used as the basis for an algorithm that allows application control over these tradeoffs.

关键词： Access control Intelligent networks File systems IP networks Permission control systems Partitioning algorithms Availability Databases Authentication

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Improving performance of TCP over wireless networks

Improving performance of TCP over wireless networks

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International conference on Distributed Computing systems

作者： B.S. Bakshi P. Krishna N.H. Vaidya D.K. Pradhan Department of Computer Science Texas A and M University College Station TX USA

Transmission control Protocol (TCP) assumes a relatively reliable underlying network where most packet losses are due to congestion. In a wireless network, however, packet losses will occur more often due to unreliable wireless links than due to congestion. When using TCP over wireless links, each packet loss on the wireless link results in congestion control measures being invoked at the source. This causes severe performance degradation. In this paper, we study the effect of: burst errors on wireless links; packet size variation on the wired network; local error recovery by the base station; and explicit feedback by the base station, on the performance of TCP over wireless networks. It is shown that the performance of TCP is sensitive to the packet size, and that significant performance improvements are obtained if a good packet size is used. While local recovery by the base station using link-level retransmissions is found to improve performance, timeouts can still occur at the source, causing redundant packet retransmissions. We propose an explicit feedback mechanism, to prevent these timeouts during local recovery. Results indicate significant performance improvements when explicit feedback from the base station is used. A major advantage of our approaches over existing proposals is that no state maintenance is required at any intermediate host. Experiments are performed using the network Simulator (NS) from Lawrence Berkeley Labs. The simulator has been extended to incorporate wireless link characteristics.

关键词： Wireless networks Base stations internet Degradation Feedback Computer science Electronic mail Protocols Computer network reliability Propagation losses

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Wideband-CDMA radio control techniques for third-generation mobile communication systems

Wideband-CDMA radio control techniques for third-generation ...

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IEEE conference on Vehicular Technology (VTC)

作者： S. Onoe K. Ohno K. Yamagata T. Nakamura NTT Mobile Communications Network Inc. Yokosuka Kanagawa Japan

The general requirements for the third-generation mobile communication system are to be markedly superior to second-generation systems in terms of services that can be provided and system economy. The wideband-CDMA (W-CDMA) system is a strong candidate for the radio access of the third-generation system. We describe a design approach that makes the most of the merits of W-CDMA, propose radio transmission and system control techniques, and present a performance evaluation of the individual techniques.

关键词： Radio control 3G mobile communication Mobile communication Multiaccess communication Web and internet services control systems Communication system control Standardization Frequency Environmental economics

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Admission control and loss management for an application-level statistical service

Admission control and loss management for an application-lev...

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International conference on network Protocols

作者： G.G. Xie S.S. Lam Department of Computer Science Naval Postgraduate School Monterrey CA USA Department of Computer Science University of Texas Austin Austin TX USA

We present an admission control framework and loss management techniques in support of a guaranteed statistical service. The service is characterized by (i) the loss rate of application data units (ADUs) bounded below a specified value, and (ii) ADU losses distributed evenly among flows subscribing to the service and uniformly over the duration of each flow. Specifically, a flow is modeled as a sequence of bursts, each of which is a sequence of packets that carry the bits of an ADU. The first packet of each burst carries information on the ADU (e.g., its bandwidth requirement). This traffic model enables admission control at the burst level as well as at the flow level. Such a two level admission control approach is very effective in bounding end-to-end ADU loss rates of flows while maintaining high channel utilization in the network. The traffic model also enables simple techniques that can be used at a network channel to distribute ADU losses evenly among flows subscribing to the same statistical service, and to protect high priority ADUs (e.g., 1 frames of MPEG applications).

关键词： Admission control Loss measurement Traffic control Application software performance loss Time measurement Communication system traffic control Delay Web and internet services Quality of service

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Neuro-fuzzy approaches to collaborative scientific computing

Neuro-fuzzy approaches to collaborative scientific computing

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International conference on Neural networks

作者： N. Ramakrishnan A. Joshi E.N. Houstis J.R. Rice Department of Computer Sciences Purdue University West Lafayette IN USA Department of CECS University of Missouri Columbia MO USA

Rapid advances in high performance computing (HPC) and the internet are heralding a paradigm shift to network-based scientific software servers, libraries, repositories and problem solving environments. According to this new paradigm, vital pieces of software and information required for a computation are distributed across a network and need to be identified and 'linked' together at run time; this implies a 'net-centric' and collaborative scenario for scientific computing. This scenario requires the application to dynamically choose the best among several competing resources that can solve a given problem. For these systems to become ubiquitous, efficient mechanisms for collaboration and automatic inference of the abilities of multiple 'compute servers' need to be established. The authors demonstrate a methodology to facilitate collaborative scientific computing. Their idea is comprised of (i) a concept of 'reasonableness' to automatically generate exemplars for learning the mapping from problems to 'servers' and (ii) a neuro-fuzzy technique developed earlier by the authors that conducts supervised classification on the exemplars generated. The techniques work in an on-line manner and cater to mutually non-exclusive classes which are critical in the collaborative networked computing landscape.

关键词： Collaboration Scientific computing network servers Collaborative software Computer networks Collaborative work High performance computing IP networks Software performance Web server

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