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Unformatted text preview: If we care about eﬃciency: – Maximize total traﬃc in network – Aà༎B: 1 unit, Bà༎C: 1, and Aà༎C, 0 – Total traﬃc rises to 2 units! A 1 B 1 C 264 29 11/4/13 The Slippery No7on of Fairness • Why is “equal per ﬂow” fair anyway? – Aà༎C uses more network resources (two links) than Aà༎B or Bà༎C – Host A sends two ﬂows, B sends one • Not produc7ve to seek exact fairness – More important to avoid starva7on – “Equal per ﬂow” is good enough 265 Generalizing “Equal per Flow” • Bokleneck for a ﬂow of traﬃc is the link that limits its bandwidth – Where conges7on occurs for the ﬂow – For Aà༎C, link A–B is the bokleneck A 1 B 10 C Bokleneck 266 30 11/4/13 Generalizing “Equal per Flow” (2) • Flows may have diﬀerent boklenecks – For Aà༎C, link A–B is the bokleneck – For Bà༎C, link B–C is the bokleneck – Can no longer divide links equally … A 1 B 10 C 267 Max Min Fairness • Intui7vely, ﬂows boklenecked on a link get an equal share of that link • Max min fair alloca7on is one that: – Increasing the rate of one ﬂow will decrease the rate of a smaller ﬂow – This “maximizes the minimum” ﬂow 268 31 11/4/13 Max Min Fairness (2) • To ﬁnd it given a network, imagine “pouring water into the network” 1. Start with all ﬂows at rate 0 2. Increase the ﬂows un7l there is a new bokleneck in the network 3. Hold ﬁxed the rate of the...
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This document was uploaded on 04/04/2014.
 Fall '09

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