Network Protocols

Preview — 3 of 10 questions

What is the correct sequence of the TCP three-way handshake when a client opens a connection to a server?

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Client                    Server
  │──── SYN ────────────────▶│  "I want to connect"
  │◀─── SYN-ACK ────────────│  "OK, I'm ready"
  │──── ACK ────────────────▶│  "Acknowledged, let's talk"
  │                           │
  │══ Data transfer begins ══│

AACK → SYN → SYN-ACK

BCONNECT → ACCEPT → CONFIRM

CSYN → ACK → SYN-ACK

DSYN → SYN-ACK → ACK

A multiplayer game needs to send player position updates 60 times per second. If a position update arrives late, it is useless — the player has already moved. Which protocol is correct?

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TCP behavior for dropped packet:
  Frame 1: pos(x=10, y=20) ✓
  Frame 2: pos(x=12, y=22) ✗ (dropped)
  TCP detects loss → STOPS sending Frame 3 → retransmits Frame 2
  Frame 2 arrives 50ms later → Frame 3 delivered → but Frame 2 is now outdated!
  Result: stuttering, head-of-line blocking

UDP behavior for dropped packet:
  Frame 1: pos(x=10, y=20) ✓
  Frame 2: pos(x=12, y=22) ✗ (dropped, ignored)
  Frame 3: pos(x=15, y=25) ✓ (delivered immediately)
  Result: one missed frame, smooth movement continues

ATCP — because guaranteed delivery ensures no position updates are lost.

BHTTP/2 — because it multiplexes streams and handles retransmission automatically.

CUDP — because low latency matters more than guaranteed delivery; a dropped position packet is better than a delayed one.

DWebSocket — because WebSocket uses a dedicated protocol for real-time data.

What problem does HTTP/2 multiplexing solve that HTTP/1.1 cannot?

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HTTP/1.1 (pipelining):
  Connection 1: Req A ──▶ [wait for A] ──▶ Res A ──▶ Req B ──▶ Res B
  Connection 2: Req C ──▶ [wait for C] ──▶ Res C
  Browser opens 6 parallel connections to work around this

HTTP/2 (multiplexing on one connection):
  Stream 1: Req A ─────────────────▶ Res A
  Stream 2: Req B ────────────▶ Res B
  Stream 3: Req C ──────────────────────▶ Res C
  (all interleaved on single TCP connection)

AHTTP/2 allows sending requests without TLS, making it faster than HTTPS.

BHTTP/2 allows servers to initiate connections to clients without a prior request.

CHTTP/2 compresses TCP headers at the network level to reduce bandwidth.

DHTTP/2 sends multiple requests and responses over a single TCP connection concurrently, eliminating head-of-line blocking at the application layer.

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