In Networking, two illustrations of congestion control are just fantastic IMO.
First one is [1], by Chiu and Jain (page 7, figure 5), showing that Additive Increase / Multiplicative decrease is the only simple policy that converges among 2 senders (with rates x and y) to a rate that is fair (along the y=x diagonal) and efficient (along the x+y=Bandwidth). This is the basis of the algorithm that made TCP (and the Internet as we know it today) possible.
The other one is this diagram from BBR [2] (from the paper in [3]), that shows how BBR sets the window ("amount in flight") to the bandwidth-delay product (BDP) of the bottleneck link (the "volume" of the pipe in a water analogy). The cool thing is that you can only measure the delay of the link if you window is <= the BDP, and you can only measure the bandwidth if your window is >= the BDP, so the algorithm has to hover around this point to make sure it can determine both.
Chiu-Jain plots are great for getting a grasp of AIMD. Another related one I like is the figure illustrating ack-clocking in Van Jacobson's original congestion control paper - Figure 1 here: https://ee.lbl.gov/papers/congavoid.pdf
First one is [1], by Chiu and Jain (page 7, figure 5), showing that Additive Increase / Multiplicative decrease is the only simple policy that converges among 2 senders (with rates x and y) to a rate that is fair (along the y=x diagonal) and efficient (along the x+y=Bandwidth). This is the basis of the algorithm that made TCP (and the Internet as we know it today) possible.
The other one is this diagram from BBR [2] (from the paper in [3]), that shows how BBR sets the window ("amount in flight") to the bandwidth-delay product (BDP) of the bottleneck link (the "volume" of the pipe in a water analogy). The cool thing is that you can only measure the delay of the link if you window is <= the BDP, and you can only measure the bandwidth if your window is >= the BDP, so the algorithm has to hover around this point to make sure it can determine both.
[1] Chiu and Jain, Analysis of the Increase and Decrease Algorithms for Congestion Avoidance in Computer Networks, 1989, https://www.cse.wustl.edu/~jain/papers/ftp/cong_av.pdf
[2] https://dl.acm.org/cms/attachment/9cf72499-b32d-4426-914b-cd...
[3] BBR: Congestion-Based Congestion Control https://queue.acm.org/detail.cfm?id=3022184