Networks: Congestion Control1 Congestion Control

Networks: Congestion Control Congestion Figure 7.50

Networks: Congestion Control3 Offered load Throughput Controlled Uncontrolled Figure 7.51

Networks: Congestion Control4 Congestion Control Host-Centric –TCP Congestion Control Mechanisms Router-Centric –Queuing Algorithms at the router

Networks: Congestion Control5 Router-Centric Congestion Queues at outgoing link drop packets to implicitly signal congestion to TCP sources. Choices in queuing algorithms: –FIFO (FCFS) Drop-Tail –Fair Queuing (FQ) –Weighted Fair Queuing (WFQ) –Random Early Detection (RED) –Explicit Congestion Notification (ECN)

Networks: Congestion Control6 Drop Tail Router FIFO queueing mechanism that drops packets when the queue overflows. Introduces global synchronization when packets are dropped from several connections.

Networks: Congestion Control7

8 Congestion window Round-trip times Slow start Congestion avoidance Congestion occurs Threshold Figure 7.63 TCP Congestion Control