TCP transforms unreliable networks into reliable communication through an elegant system of trust-building: handshakes that prove mutual reachability, sequence numbers that track every byte, and acknowledgments that confirm receipt.
Nagle's algorithm was brilliant in 1984—batching tiny packets saved the bandwidth-starved Internet from drowning in overhead. Four decades later, it's often the reason your game feels sluggish or your terminal lags. Here's when to embrace it, when to kill it with TCP_NODELAY, and why the answer has flipped.
TCP senders are blind to network conditions, yet must avoid overwhelming shared infrastructure. Through inference, restraint, and algorithms that read silence as signal, congestion control prevents the Internet from collapsing under its own success.
TCP's three-way handshake forces every connection to pay a round-trip tax before sending data. TCP Fast Open lets returning clients skip the formalities—bundling their request into the very first packet.
FIN ends a TCP connection like hanging up after saying goodbye. RST ends it like the line going dead mid-sentence. Knowing which happened—and why—is the difference between debugging for minutes and debugging for hours.
TCP's sliding window gives receivers a way to say 'slow down' without losing data. Here's how window advertisements, scaling, and zero-window probes keep fast senders from overwhelming slow receivers.
A crashed server can't say goodbye—it just vanishes. TCP keep-alive is how the survivors find out, reclaim resources, and move on.
TCP options are how a 1970s protocol survives in a gigabit world—negotiating segment sizes to avoid fragmentation, scaling windows beyond their original 64KB limit, and using timestamps to keep high-speed connections sane.
TCP doesn't trust the network. Every packet carries an implicit question—did you get this?—and silence is treated as loss. Here's how TCP detects missing data and recovers from it.
TCP assigns a sequence number to every byte and demands acknowledgment of receipt—a simple system that transforms chaotic, unreliable networks into dependable communication.
TCP's three-way handshake solves a fundamental problem: how do two machines that have never met agree on a shared reality before exchanging data? The answer involves sequence numbers, mutual acknowledgment, and a vulnerability that attackers exploit.
When you close a TCP connection, it haunts your system for 60 seconds. TIME_WAIT isn't a bug—it's TCP refusing to forget until the network catches up.
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