1,721,160 research outputs found
On Calibrating Measurements of Packet Transit Times
No full textWe discuss the problem of detecting errors in measurements of the total delay experienced by packets transmitted through a wide-area network. We assume that we have measurements of the transmission times of a group of packets sent from an originating host, A, and a corresponding set of measurements of their arrival times at their destination host, B, recorded by two separate clocks. We also assume that we have a similar series of measurements of packets sent from B to A (as might occur when recording a TCP connection), but we do not assume that the clock at A is synchronized with the clock at B, nor that they run at the same frequency. We develop robust algorithms for detecting abrupt adjustments to either clock, and for estimating the relative skew between the clocks. By analyzing a large set of measurements of Internet TCP connections, we find that both clock adjustments and relative skew are sufficiently common that failing to detect them can lead to potentially large errors when an..
An Analysis of Using Reflectors for Distributed Denial-of-Service Attacks
No full textAbstract — Attackers can render distributed denial-of-service attacks more difficult to defend against by bouncing their flooding traffic off of reflectors; that is, by spoofing re-quests from the victim to a large set of Internet servers that will in turn send their combined replies to the victim. The resulting dilution of locality in the flooding stream compli-cates the victim’s abilities both to isolate the attack traffic in order to block it, and to use traceback techniques for lo-cating the source of streams of packets with spoofed source addresses, such as ITRACE [Be00a], probabilistic packet marking [SWKA00], [SP01], and SPIE [S+01]. We discuss a number of possible defenses against reflector attacks, find-ing that most prove impractical, and then assess the degree to which different forms of reflector traffic will have char-acteristic signatures that the victim can use to identify and filter out the attack traffic. Our analysis indicates that three types of reflectors pose particularly significant threats: DNS and Gnutella servers, and TCP-based servers (particularly Web servers) running on TCP implementations that suffer from predictable initial sequence numbers. We argue in con-clusion in support of “reverse ITRACE ” [Ba00] and for the utility of packet traceback techniques that work even for low volume flows, such as SPIE. I
A Survey of Support For Implementing Debuggers
No full textThe degree to which hardware and operating systems support debugging strongly influences the caliber of service that a debugger can provide. We survey the different forms in which such support is available. We limit our survey to lower-level debugger design issues such as accessing the debugged program's state and controlling its execution. The study concentrates on those types of support that make overall debugger performance efficient and that support debugger features for ferreting out hard-to-find bugs. We conclude with an overview of state-of-the-art debuggers and a proposal for a new debugger design
Towards a Framework for Defining Internet Performance Metrics
No full textThe Internet's tremendous growth represents a triumph of standardization, since it is only through standardization that so many different networks using so many different designs can smoothly exchange data. The standardization of Internet measurement, however, has not matched the explosive growth of the network as a whole. Even such basic notions as how to measure the throughput or delay along an Internet path lack a standardized framework. Instead it has become increasingly difficult to diagnose problems or determine whether one is receiving promised performance. In this paper we outline how a measurement framework might be developed to support Internet diagnosis and performance evaluation. We propose terminology to use in defining standards, including the key notions of metric as the fundamental property we wish to measure, methodology as a way to attempt to measure the property, and measurement as the result of a specific application of a methodology. We develop a basic contrast be..
Growth Trends in Wide-Area TCP Connections
No full textWe analyze the growth of a large research laboratory's widearea TCP connections over a period of three years. Our data consisted of seven month-long traces of all TCP connections made between the site and the rest of the world. We find that many TCP protocols exhibited exponential growth in the number of connections made and bytes transferred, even though the number of hosts at the site only grew linearly. The exponential growth of most of the major TCP protocols began tapering off with the final datasets, while relatively new information-retrieval protocols such as Gopher and WorldWide Web exhibited explosive growth during the same time. Our study also found that individual users greatly affected the site's traffic profile by the inadvertent or casual initiation of multiple, periodic wide-area connections; that exponential growth is fed in part by more users "discovering" the Internet and in part by existing users increasingly incorporating use of the Internet into their work patterns..
Fast, approximate synthesis of fractional gaussian noise for generating self-similar network traffic
No full textRecent network traffic studies argue that network arrival processes are much more faithfully modeled using statistically self-similar processes instead of traditional Poisson processes [LTWW94, PF95]. One difficulty in dealing with selfsimilar models is how to efficiently synthesize traces (sample paths) corresponding to self-similar traffic. We present a fast Fourier transform method for synthesizing approximate self-similar sample paths for one type of self-similar process, Fractional Gaussian Noise, and assess its performance and validity. We find that the method is as fast or faster than existing methods and appears to generate close approximations to true self-similar sample paths. We also discuss issues in using such synthesized sample paths for simulating network traffic, and how an approximation used by our method can dramatically speed up evaluation of Whittle's estimator for H, the Hurst parameter giving the strength of long-range dependence present in a self-similar time series
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