Congestion Control

Congestion Control - February 13, 2012 Veton Këpuska 1...

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Unformatted text preview: February 13, 2012 Veton Këpuska 1 Computer Networks 2 Congestion Control February 13, 2012 Veton Këpuska 2 Congestion Control Algorithms The situation when to many packets are present in subnet it is called congestion . Congestion Traffic Performance Chart as function of Number of Packets Sent 0.2 0.4 0.6 0.8 1 1.2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Number of Packets in Mil. Packets Delivered [%] Desirable Performance Congested Performance Ideal Maximum Carrying capacity of subnet February 13, 2012 Veton Këpuska 3 Congestion Factors Streams of inputs packets arriving from multiple lines (3-4 or more) needing the same output line => queue buildup. Adding more memory may help to a point but – a study by Nagle suggest that increasing memory to ∞ to accommodate larger queues congestions gets worse not better due to time required to get to the front of the queue (timed out). Slow Processors: Queue build up due to routers slow CPU’s at performing bookkeeping task: Queueing buffers, Updating tables, etc. Low bandwidth lines. Typically the problem is that upgrading one part of the system shifts the bottleneck to the someplace else. The real problem frequently is a mismatched parts of the system. The problem will persist until all components of the system are in balance. February 13, 2012 Veton Këpuska 4 Congestion Control vs. Flow Control Congestion Control has to due with making sure the subnets are able to carry the offered traffic. Thus it is a global issue involving the behavior of all the hosts, all the routers, the store-and forwarding processing within the routers, and all the other factors that tend to diminish the carrying capacity of the subnet. Flow Control relates to point-to-point traffic between a given sender and a given receiver. Its job is to make sure that a fast sender cannot continually transmit data faster than the receiver is able to absorb it. It frequently involves some direct feedback from the receiver to the sender to tell the sender how things are doing at the other end. February 13, 2012 Veton Këpuska 5 Congestion Control vs. Flow Control Example Flow Control Problem: Consider a fiber optic network with a capacity of 1000 Gbps on which a supercomputer is trying to transfer a file to a personal computer at 1 Gbps. Although there is no congestion the supercomputer has to frequently stop in order to allow PC to catch up....
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This note was uploaded on 02/11/2012 for the course ECE 5535 taught by Professor Staff during the Spring '10 term at FIT.

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Congestion Control - February 13, 2012 Veton Këpuska 1...

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