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Hectal
Phase 2Intermediate3 of 8 in Networking

Transport: TCP, UDP & Ports

Ports and sockets, the TCP handshake and teardown, reliability and congestion control, connection states like TIME_WAIT, and when UDP (and QUIC) is the better choice.

IP gets packets to the right host. The transport layer gets bytes to the right PROGRAM, and TCP makes that delivery reliable and ordered. Almost every production mystery involving timeouts, 'connection reset', or exhausted ports lives here.

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4 topics ~28 min 5 code blocks & diagrams
Start with the first topic
1
2.1

Ports, Sockets & Connections

A port identifies a program on a host; a connection is uniquely identified by five values: protocol, source IP, source port, destination IP, destination port.

7 min 1 code practice

2
2.2

The TCP Handshake and Teardown

TCP opens every connection with a three-way handshake (SYN, SYN-ACK, ACK) and closes it with FIN/ACK exchanges or an abrupt RST; each costs round trips, which is why connection reuse matters so much.

7 min 1 diagram 1 code practice

3
2.3

Reliability, Flow Control, Congestion & Connection States

TCP guarantees ordered, reliable delivery with sequence numbers, acknowledgements, and retransmission, adapts its speed to the receiver and the network, and moves through states like ESTABLISHED, TIME_WAIT, and CLOSE_WAIT that tell you what's happening.

7 min 1 code practice

4
2.4

UDP, and QUIC Built on Top of It

UDP sends independent datagrams with no connection, ordering, or retransmission; it's the right choice when speed matters more than perfection, and it's the foundation of QUIC and HTTP/3.

7 min 1 code practice