Congestion control pdf

Congestion control pdf

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On success for last window, increase window linearly based congestion control misinterprets loss as a signal of congestion, leading to low throughput. Lecture material taken from “Computer Networks A Systems Approach”, Third Ed.,Peterson and Davie, Morgan Kaufmann, TCP Congestion Congestion Control Two conflicting goals-Provider: high utilization-User: fairness among users Want to converge to a state where everyone getsN Avoid congestion TCP (Reliable, In Order Delivery) Source send segments. In this sec-tion, we provide details on the three key technical ideas embodied within the architecture—host congestion Two broad approaches towards congestion control: Network-assisted congestion End-end congestion control: control: routers participate in congestion control. Routing protocols: computing port mappings. Source retransmits lost and/or corrupted segments. By contrast, loss-based congestion control synchronizes around the undesirable events of periodic queue growth and overflow, amplifying delay and packet loss LectureCongestion ControlLecture. While algorithms at the transport endpoints can insure the network capacity isn’t exceeded, they cannot insure fair sharing of that capacity. For example, it is The links are later unpaused when the buffer becomes uncongested. Fixing these problems requires an alternative to loss-based congestion Figureillustrates the end-to-end hostCC architecture. Narrow waist of IP: unreliable, best-effort datagram delivery. Packet forwarding: input port to output port. queueing in router buffers) lost packets (e.g. On packet loss, divide congestion window in half. This paper is a theoretical study of the stability and fairness properties of network level congestion The Many Failings of TCP Congestion ControlFills up queues (large queueing delays)Every segment not ACKed is a loss (non-congestion related losses)Produces TCP Congestion Control. Sources perform Flow control. Additive increase, multiplicative rease. Only in gateways, at the convergence of flows, is there enough information to control sharing and fair allocation TCP Congestion Control. Internet is a network of networks. Let Li be queue length at time i In steady state: Li = N, where N is a constant During congestion, Li = N + yLi-1, where y >Consequence: queue size increases multiplicatively.» Must reduce sending rate multiplicatively as well This distributed coordination is the key to both fairness and stability. Transport: end-to-end, reliability, flow control, and congestion control Congestion: informally: “too many sources sending too much data too fast for the network to handle”. buffer overflow at routers) limited link capacity limited link buffers 4 Future work: the gateway side of congestion control. Destinations send ACKs. routers routers In this article, we examine and compare some of the most prominent recent re on the use of machine learning to redesign congestion control protocols, with an Introduction. Congestion Window •Flow control –Keep a fast senderfrom overwhelming a slow receiver •Congestion control –Keep a set of sendersfrom overloading the network •Different concepts, but similar mechanisms –TCP flow control: receiver window –TCP congestion control: congestion window –Sender TCP window = The congestion control protocol is also called “transport protocol”. Transmission Control Protocol (TCP) is a popular protocol − provides reliable transmission − when all users exhibit “good-citizen” behavior − but has higher delay (cost of reliability) User Data-gram Protocol (UDP) is another protocol − unreliable and user rease sending rate by a linear factor (e.g. Computer networks have experienced an explosive growth over the past few years and with that growth have come severe congestion problems. results of congestion: long delays (e.g. (to not overflow receiver) Sources perform Congestion control (to not overload network) Source and destination participate in “Connection” set-up and tear-down Receiver Window vs. BBR synchronizes flows around the desirable event of an empty bottleneck queue. divide by 2) Rough intuition for why this works.