Lectures22_23

Lectures22_23 - QuickTime and a GIF decompressor are needed...

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QuickTime™ and a GIF decompressor are needed to see this picture. QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. LIDS Lectures 22 & 23 Flow and congestion control Eytan Modiano Eytan Modiano Slide 1 Laboratory for Information and Decision Systems
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FLOW CONTROL QuickTime™ and a GIF decompressor are needed to see this picture. QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. LIDS Flow control: end-to-end mechanism for regulating traffic between source and destination Congestion control: Mechanism used by the network to limit congestion The two are not really separable, and I will refer to both as flow control In either case, both amount to mechanisms for limiting the amount of traffic entering the network Sometimes the load is more than the network can handle Eytan Modiano Slide 2 Laboratory for Information and Decision Systems
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WITHOUT FLOW CONTROL QuickTime™ and a GIF decompressor are needed to see this picture. QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. LIDS When overload occurs queues build up packets are discarded Sources retransmit messages congestion increases => instability Flow control prevents network instability by keeping packets waiting outside the network rather than in queues inside the network Avoids wasting network resources Prevent “disasters” Eytan Modiano Slide 3 Laboratory for Information and Decision Systems
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OBJECTIVES OF FLOW CONTROL QuickTime™ and a GIF decompressor are needed to see this picture. QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. LIDS Maximize network throughput Reduce network delays Maintain quality-of-service parameters Fairness, delay, etc. . Tradeoff between fairness, delay, throughput… Eytan Modiano Slide 4 Laboratory for Information and Decision Systems
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FAIRNESS QuickTime™ and a GIF decompressor are needed to see this picture. QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. LIDS Session 1 Session 2 Session 3 Session 4 If link capacities are each 1 unit, then Maximum throughput is achieved by giving short session one unit and zero units to the long session; total throughput of 3 units One concept of fairness would give each user 1/2 unit; total throughput of 2 units Alternatively, giving equal resources to each session would give single link users 3/4 each, and 1/4 unit to the long session Eytan Modiano Slide 5 Laboratory for Information and Decision Systems
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FAIRNESS QuickTime™ and a GIF decompressor are needed to see this picture. QuickTime™ and a Photo - JPEG decompressor are needed to see this picture.
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Lectures22_23 - QuickTime and a GIF decompressor are needed...

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