Bandwidth for High Speed Networks

# The estimated rate of ow i ri is updated every time a

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Unformatted text preview: time and length of the k packet of ow i. The estimated rate of ow i, ri , is updated every time a new packet is received: k 3 rinew = 1 , e,Tik =K  lik + e,Tik =K riold ; Ti where Tik = tk , tk,1 and K is a constant. We discuss i i the rationale for using the form e,Tik =K for the exponential weight in Section 2.7. In the longer version of this paper 22 we show that, under a wide range of conditions, this estimation algorithm converges. 2.2.2 Link Fair Rate Estimation In this section, we present an estimation algorithm for t. To give intuition, consider again the uid model in Section 2.1 where the arrival rates are known exactly, and assume the system performs the probabilistic dropping algorithm according to Eq. 2. Then, the rate with which the algorithm accepts packets is a function of the current estimate of the fair share rate, which we denote by bt. Letting F  bt denote this acceptance rate, we have F  bt = n X i=1 min ri t; bt : 4 Note that F  is a continuous, nondecreasing, concave, and piecewise-linear function of b. If the link is congested At C  we choose bt to be the unique solution to F x = C . If the link is not congested At C  we take bt to be the largest rate among the ows that traverse the link, i.e., bt = max1in ri t. From Eq 4 note that if we knew the arrival rates ri t we could then compute t directly. To avoid having to keep such per- ow state, we seek instead to implicitly compute bt by using only aggregate measurements of F and A. We use the following heuristic algorithm with three aggregate state variables: b, the estimate for the fair share b b rate; A, the estimated aggregate arrival rate; F , the estimated rate of the accepted tra c. The last two variables b are updated upon the arrival of each packet. For A we use exponential averaging with a parameter e,T=K where T is the inter-arrival time between the current and the previous packet: l b b 5 Anew = 1 , e,T=K  T + e,T=K Aold b b where Aold is the value of A be...
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## This document was uploaded on 03/04/2014 for the course ENG 531 at Rice.

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