L29 - Congestion control Traffic congestion in networks is...

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Congestion control Traffic congestion in networks is a serious problem. Total throughput drops with offered traffic beyond some point, unless input is controlled. Show Figure 5-25. Increased delay leads to acknowledgment timeouts, retransmissions. Large delay is unacceptable for many applications.
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Congestion control tools 1. Route the traffic efficiently. (But if too much traffic, not sufficient.) 2. Tools to learn of congestion problem: a) Routing reports of congestion. b) End-to-end probe packet - measure delay. c) Allow packet-switching nodes to add congestion information to packets as they go by. # Opposite to congestion direction to information source. # In congestion direction so destination can inform source.
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Congestion control tools (continued) 3. Use methods to cut back the offered load. a) Control packet to source nodes, asking them to limit input. b) Require sources to limit rate. c) Refuse or limit new connections. d) Window flow control or permissions 4. Discard some packets, possibly on a priority basis.
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Factors affecting congestion Show Fig. 5-26
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Admission control Choice of route Knowledge, negotiation or enforcement of type and amount of traffic the connection will generate. Refusal of a connection also is possible.
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This note was uploaded on 09/23/2009 for the course CMPEN 362 taught by Professor Johnmetzner during the Spring '09 term at Pennsylvania State University, University Park.

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L29 - Congestion control Traffic congestion in networks is...

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