What Is TCP/IP
TCP/IP is the protocol family (a set of rules) used by the Internet: devices exchange data according to these rules. It is organized in layers, each with its own job — like sending a package: the application layer writes the content (HTTP/MQTT data), the transport layer attaches the shipping label (TCP/UDP ports), the network layer writes the destination address (IP address), and the link layer does the actual transport (Wi-Fi/Ethernet).
In plain words: the IP address decides "who to send to", the port number decides "which program", and TCP/UDP decides "how it is delivered" — TCP is like registered mail (receipt, reliable, a bit slower), UDP is like regular mail (no guarantee, fast).
TCP vs. UDP
TCP (Transmission Control Protocol): connection-oriented. It establishes a connection with a three-way handshake first; data arrives in order and is retransmitted if lost. Suitable for reliable applications: file transfer, web pages, MQTT, remote login.
UDP (User Datagram Protocol): connectionless. Once sent, it is not tracked; delivery is not guaranteed and packets may arrive out of order. Suitable for real-time/broadcast scenarios: audio/video, games, device discovery (broadcast/multicast).
Port: a number from 0 to 65535; ports below
1024are common service ports (HTTP 80, HTTPS 443, MQTT 1883).
Socket Programming Model
The SDK uses lwIP's BSD Socket API (socket / bind / connect / listen / accept / send / recv, etc.), almost the same as writing network programs on a PC.
Client: socket() creates the socket → connect() connects to the server → send/recv exchange data.
Server: socket() → bind() binds the port → listen() listens → accept() accepts a connection → recv/send communicates with the client.
Network Pages in This Section
The experiment pages related to TCP/IP in this section all share the same Wi-Fi example skeleton:
| Page | Protocol | Role | SDK example |
|---|---|---|---|
| TCP Client | TCP | Client (connects to a server) | examples/wifi/sta/wifi_tcp |
| TCP Server | TCP | Server (waits for connections) | examples/wifi/sta/wifi_tcp |
| UDP Client | UDP | Client | Self-authored |
| UDP Server | UDP | Server (echo) | examples/wifi/sta/wifi_udp |
| UDP Broadcast / UDP Multicast | UDP | One-to-many | Self-authored |
FAQ
Q: Which is better, TCP or UDP? Neither is universally better: choose TCP for reliability, UDP for speed/broadcast. Use TCP when delivery must be confirmed (e.g. control commands); use UDP for real-time audio/video and device discovery.
Q: What happens if the port is wrong? A client cannot connect to the server or receive data; a server that fails to bind prints a bind error. Common ports: HTTP 80, HTTPS 443, MQTT 1883, MQTTS 8883.
Q: Why can the TCP server only handle one client? The example is a single-connection demo (it
accepts one client and loops); in real products, create a task per connection to support multiple clients.
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