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Implement a Simple Congestion Control Algorithm

hard7/8

Implement TCP Connection Teardown (FIN/ACK Sequence)Use a TUN/TAP Interface to Inject Your TCP Stack

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Compiler

2.0s Limit 256MB

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Implementation

Implement a simulation of TCP congestion control.

Requirements:

Initialize cwnd = 1 MSS and ssthresh = 64 KB
Implement slow start: double cwnd each RTT until ssthresh
Implement congestion avoidance: linear growth (+1 MSS per RTT)
Simulate packet loss with both timeout and 3 duplicate ACKs
On timeout: set ssthresh = cwnd/2, cwnd = 1 MSS
On fast recovery: set ssthresh = cwnd/2, cwnd = ssthresh + 3*MSS
Show AIMD behavior: additive increase, multiplicative decrease
Print cwnd and ssthresh after each event

Why This Matters

The Reno-style AIMD you implement here was the Linux default until 2006, when CUBIC replaced it as the kernel's tcp_congestion_control default; Google's BBR, used across YouTube and Google Cloud, takes an entirely different model-based approach precisely because AIMD's sawtooth wastes bandwidth on high-BDP links. Every video call or file download you do rides on one of these algorithms deciding, packet by packet, how hard to push the network.

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main.c

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