TAILIEUCHUNG - Network Congestion Control Managing Internet Traffic phần 8

tự tương quan chức năng của một phân bố Poisson hội tụ không. Các tác giả (Paxson và Floyd 1995) giải thích rõ chính xác điều này có nghĩa: nếu lưu lượng truy cập Internet sẽ theo một quá trình Poisson, và bạn sẽ nhìn vào một dấu vết giao thông, nói rằng, | . THE NATURE OF INTERNET TRAFFIC 183 autocorrelation function of a Poisson distribution converges to zero. The authors of Paxson and Floyd 1995 clearly explain what exactly this means if Internet traffic would follow a Poisson process and you would look at a traffic trace of say five minutes and compare it with a trace of an hour or a day you would notice that the distribution flattens as the timescale grows. In other words it would converge to a mean value because a Poisson process has an equal amount of upward and downward motion. However if you do the same with real Internet traffic you may notice the same pattern at different timescales. When it may seem that a 10-min trace shows a peak and there must be an equally large dip if we look at a longer interval this may not be so in the case of real Internet traffic - what we saw may in fact be a small peak on top of a larger one this can be described as peaks that sit on ripples that ride on waves . This recurrence of patterns is what is commonly referred to as self-similarity - in the case of Internet traffic what we have is a self-similar time series. It is well known that self-similarity occurs in a diverse range of natural sociological and technical systems in particular it is interesting to note that rainfall bears some similarities to network traffic - the same mathematical model a fractional autoregressive integrated moving average fARIMA process can be used to describe both the time series Gruber 1994 Xue et al. 1999 .2 The fact that there is no theoretic limit to the timescale at which dependencies can occur . you cannot count on the aforementioned flattening towards a mean no matter how long you wait has the unhappy implication that it may in fact be impossible to build a dam that is always large Translated into the world of networks this means that the self-similar nature of traffic does have some implications on the buffer overflow probability it does not decrease exponentially with a .

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