Episode 1 — Fundamentals / 1.3 — Internet Protocols

1.3 — Internet Protocols: Quick Revision

Compact cheat sheet. Print-friendly.

How to use this material (instructions)

Skim top-to-bottom in one pass before quizzes or interviews.
If a row feels fuzzy — open the matching lesson: README.md → 1.3.a…1.3.e.
Deep practice — 1.3-Exercise-Questions.md.
Polish phrasing — 1.3-Interview-Questions.md.

TCP vs UDP (master table)

	TCP	UDP
Connection	Yes (handshake)	No
Reliability	Retransmit + order	Best-effort
Flow control	Yes	No
Congestion control	Yes	No (apps may add)
Header (typical min)	20+ bytes	8 bytes
Common uses	HTTP/1.1–2, SSH, SMTP	DNS (small), QUIC base, VoIP, games

TCP 3-way handshake

Client                         Server
  |-- SYN ---------------------->|
  |<-- SYN-ACK ------------------|
  |-- ACK ---------------------->|
  |        ESTABLISHED            |

Key terms (one-liners)

Term	One-liner
ISN	Initial sequence number; starting point for byte tracking
ACK	Acknowledges bytes received; drives retransmissions
RTT	Round-trip time; drives timeouts and CC behavior
SYN flood	Half-open connection exhaustion attack
SYN cookies	Avoid storing full state until ACK proves legitimacy
QUIC	UDP-based transport with TLS 1.3 + streams (HTTP/3)
HOL blocking	Later work blocked waiting on an earlier lost segment

“Which protocol?” quick picks

Need	Pick
Must not lose bytes / strict order	TCP (or QUIC streams with app semantics)
Minimize setup latency for tiny messages	Often UDP (DNS)
Web at scale with modern stacks	HTTP/3 / QUIC
Stealth / anonymity	Not TCP/UDP lesson — wrong tool; VPN/Tor are different layers

← Back to 1.3 — Internet Protocols (README)