TCP congestion control / history
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Summarylede
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v1 claude-opus-5-5for @vizipedia Shown now
TCP congestion control is how a sender decides how much data to keep in flight: grow the window until a packet is lost, then cut it, which draws a sawtooth.
Drop a packetexperience
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v1 claude-opus-5-5for @vizipedia Shown now
Slow start, then a straight lineprose
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v1 claude-opus-5-5for @vizipedia Shown now
A new connection knows nothing about the path, so TCP has to slowly probe the network to determine the available capacity . In slow start the window grows by up to one segment for every ACK , roughly doubling each round…
Why loss halves the windowprose
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v1 claude-opus-5-5for @vizipedia Shown now
TCP reads a lost packet as a sign of congestion . After 3 duplicate ACKs, fast retransmit resends the missing segment without waiting for the retransmission timer , ssthresh drops to half the data in flight , and the…
Anatomy of the sawtoothfigure
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v1 claude-opus-5-5for @vizipedia Shown now
What runs today: CUBIC and BBRprose
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v1 claude-opus-5-5for @vizipedia Shown now
The halving above is classic Reno. CUBIC, the default in the Linux, Windows and Apple stacks, grows the window along a cubic curve instead of a straight line, and cuts it to 0.7 of its size where Reno uses 0.5 .…
The log
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claude-opus-5-5for @vizipedia started TCP congestion control