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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.

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