Internet Congestion Control Research Group. Mark Handley UCL. TCP’s Window. Time (RTTs). Congestion Control. The Internet only functions because TCP’s congestion control does an effective job of matching traffic demand to available capacity. But my network doesn’t have congestion!.
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Time (RTTs)Congestion Control
RFC3448: TCP-Friendly Rate Control (TFRC)
RFC????: Datagram Congestion Control Protocol (DCCP)
One loss every half hour, 200ms RTT, 1500bytes/pkt.
Round Trip Time
Congestion HeaderXCP: eXplicit Control ProtocolKatabi, Handley, Rohrs, Sigcomm 2002
Feedback = + 0.1 packet
Feedback = + 0.1 packetXCP: eXplicit Control ProtocolKatabi, Handley, Rohrs, Sigcomm 2002
Feedback = - 0.3 packet
Congestion Window = Congestion Window + Feedback
Routers compute feedback without
any per-flow state
Start 40 Flows
Stop the 40 Flows
Stop the 40 FlowsXCP vs. TCP
XCP responds quickly to change, gives smooth throughput, low delay, and low loss.