Why architecture matters here

TCP failures — bufferbloat, congestion collapse, RTT-limited throughput — trace to specific algorithms. Architecture matters because tuning algorithm + buffers + kernel decides real-world performance.

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The architecture: every piece explained

The top strip is setup + delivery. 3-way handshake SYN/SYN-ACK/ACK. Sequence + ack ensure reliable ordering. Congestion control — CUBIC default, BBR for high-BDP. Window scaling allows beyond 64KB windows.

The middle row is recovery. Slow start ramps up. Fast retransmit on 3 dup ACKs. Nagle + delayed ACK can interact badly. SACK + FRTO improve recovery.

The lower rows are ops. TIME_WAIT closing state affects reuse. TCP tuning via sysctl + BBR. Ops — observability + kernel + long-fat pipes.

TCP — 3WHS + congestion + window + BBR + Naglethe reliable byte stream that runs the internet3-way handshakeSYN/SYN-ACK/ACKSequence + ackreliable bytesCongestion controlCUBIC / BBRWindow scalingbeyond 64KBSlow startramp upFast retransmit3 dup ACKsNagle + delayed ACKbatch tinySACK + FRTOrecoveryTIME_WAITclosing stateTCP tuningsysctl + BBROps — observability + kernel + long-fat pipesstartrecovercoalesceresilienthandletunetuneoperateoperate
TCP internals: handshake + congestion + recovery.
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End-to-end flow

End-to-end: connection opens with 3WHS. Slow start ramps window. Loss triggers fast retransmit + reduces cwnd. BBR tracks bottleneck bandwidth + RTT for higher throughput on long-fat pipes. Close 4-way; TIME_WAIT prevents late segment issues.