1. Networks: Congestion Control1 Congestion Control

2. Networks: Congestion Control2 4 8 6 3 2 1 5 7 Congestion Figure 7.50

3. Networks: Congestion Control3 Offered load Throughput Controlled Uncontrolled Figure 7.51

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

5. 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)

6. 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.

7. Networks: Congestion Control7

8. 8 Congestion window 10 5 15 20 0 Round-trip times Slow start Congestion avoidance Congestion occurs Threshold Figure 7.63 TCP Congestion Control