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--- skills:network [2026/06/17 13:20] – [Layer 4: Transport] phong2018
+++ skills:network [2026/06/17 13:29] (current) – phong2018
@@ Line 16: / Line 16: @@
 **Purpose:** Define application rules and message formats.
-**Examples Protocol: **
+**Application-layer protocols**
+These protocols operate at the **Application Layer (Layer 7)** and define how applications exchange data.
+^ Protocol ^ Full Name ^ Typical Transport Layer ^ Common Use Cases ^
+| HTTP | HyperText Transfer Protocol | TCP | Web pages, REST APIs |
+| HTTPS | HTTP over TLS/SSL | TCP | Secure web pages, secure APIs |
+| WebSocket | Full-duplex web communication protocol | TCP | Real-time chat, notifications, live updates |
+| RESP | Redis Serialization Protocol | TCP | Communication between Redis clients and servers |
+| AMQP | Advanced Message Queuing Protocol | TCP | Message brokers such as RabbitMQ |
+| Kafka Protocol | Apache Kafka binary protocol | TCP | Event streaming and distributed messaging |
+| SMTP | Simple Mail Transfer Protocol | TCP | Sending email |
+| FTP | File Transfer Protocol | TCP | File uploads and downloads |
+| DNS | Domain Name System | UDP (mostly), TCP (sometimes) | Domain name resolution |
+| MQTT | Message Queuing Telemetry Transport | TCP | IoT devices and lightweight messaging |
+===== Notes =====
+* These are **application-layer protocols**, not transport protocols.
+* Most application protocols rely on **TCP** because they require reliable and ordered delivery.
+* **DNS** primarily uses **UDP** for low latency, but switches to **TCP** for large responses and zone transfers.
+* **HTTPS** is essentially:
+<code>
+HTTPS = HTTP + TLS + TCP
+</code>
+* **WebSocket** starts with an HTTP handshake, then upgrades to a persistent TCP connection.
+<code>
+Client
+  ↓
+Application Protocol (HTTP, MQTT, AMQP, RESP)
+  ↓
+Transport Protocol (TCP or UDP)
+  ↓
+IP
+  ↓
+Ethernet / Wi-Fi
+</code>
+===== Examples =====
+<code>
+HTTP/1.1 → TCP → IP → Ethernet
+WebSocket → TCP → IP → Ethernet
+DNS → UDP → IP → Ethernet
+MQTT → TCP → IP → Ethernet
+Kafka → TCP → IP → Ethernet
+HTTPS → TLS → TCP → IP → Ethernet </code>
-* HTTP / HTTPS
-* WebSocket
-* Redis Protocol (RESP)
-* AMQP (RabbitMQ)
-* Kafka Protocol
-* SMTP
-* FTP
-* DNS
-* MQTT
 **Examples of messages:**
@@ Line 76: / Line 121: @@
 **Purpose:** Deliver data between processes.
-==== Transport-layer protocols.====
+^ Feature ^ TCP ^ UDP ^
+| Full Name | Transmission Control Protocol | User Datagram Protocol |
-==== TCP ====
+| Connection Type | Connection-oriented | Connectionless |
+| Reliability | Reliable delivery with ACK and retransmission | Best effort, no delivery guarantee |
-* Connection-oriented
+| Message Ordering | Preserves packet order | No ordering guarantee |
-* Reliable delivery
+| Error Recovery | Automatic retransmission | No retransmission |
-* Ordered messages
+| Flow Control | Yes (sliding window) | No |
-* Retransmission support
+| Congestion Control | Yes | No |
+| Overhead | Higher | Lower |
-Used by:
+| Latency | Higher | Lower |
+| Speed | Slower due to reliability mechanisms | Faster due to minimal overhead |
-* HTTP/1.1
+| Header Size | 20–60 bytes | 8 bytes |
-* HTTP/2
+| Communication Style | Continuous connection between client and server | Independent datagrams |
-* WebSocket
+| Typical Use Cases | Web applications, databases, messaging systems | Real-time communication, gaming, streaming |
-* Redis
-* RabbitMQ
-* Kafka
-==== UDP ====
-* Connectionless
-* Faster
-* No delivery guarantee
-Used by:
+^ Common Protocols and Applications ^ Transport Layer ^
+| HTTP/1.1 | TCP |
+| HTTP/2 | TCP |
+| WebSocket | TCP |
+| Redis (RESP) | TCP |
+| RabbitMQ (AMQP) | TCP |
+| Apache Kafka Protocol | TCP |
+| SMTP | TCP |
+| FTP | TCP |
+| SSH | TCP |
+| DNS | UDP (primarily), TCP (zone transfer and large responses) |
+| VoIP | UDP |
+| Online Games | UDP |
+| WebRTC | UDP |
+| QUIC | UDP |
+| HTTP/3 | QUIC over UDP |
-* DNS
+^ Summary ^ TCP ^ UDP ^
-* VoIP
+| Main Goal | Reliability and correctness | Speed and low latency |
-* Online games
+| Best For | Data that must not be lost | Data that must arrive quickly |
-* WebRTC
+| Example | File download, API requests, email | Video call, live stream, multiplayer game |
-* QUIC (HTTP/3)
+| Real-world Analogy | Registered mail with delivery confirmation | Radio broadcast |
 ===== Layer 3: Network =====