Data Transmission and Networking | 数据传输与网络

📚 Data Transmission and Networking | 数据传输与网络

Data transmission is the movement of digital data between devices, while networking is the practice of connecting devices so they can exchange data. This topic covers how messages are broken into packets, how errors are detected, how data is kept secure, and how devices are organised into local and wide area networks. It is a core topic for Cambridge IGCSE and O Level Computer Science.

数据传输是数字数据在设备之间的移动，而网络是将设备连接起来以便交换数据的实践。本主题涵盖消息如何拆分为数据包、如何检测错误、如何保证数据安全，以及设备如何组织成局域网和广域网。这是 Cambridge IGCSE 和 O Level 计算机科学的核心主题。

1. Data Packets and Packet Switching | 数据包与分组交换

A data packet is a small block of data sent over a network. It usually contains three parts: a header, a payload and a trailer. The header includes the source and destination IP addresses, the packet sequence number and the protocol used. The payload is the actual data being carried, and the trailer contains error-checking information.

数据包是通过网络发送的小数据块。它通常包含三个部分：报头、有效载荷和报尾。报头包含源 IP 地址和目的 IP 地址、数据包序列号以及使用的协议。有效载荷是所携带的实际数据，报尾包含错误检查信息。

Packet switching breaks a large message into packets that travel independently across a network. Routers read the header of each packet and forward it along the best available path. At the destination, the packets are reassembled into the correct order using the sequence numbers.

分组交换将大消息拆分为在网络上独立传输的数据包。路由器读取每个数据包的报头，并沿最佳可用路径转发。在目的地，数据包利用序列号按正确顺序重新组装。

2. Transmission Modes: Simplex, Half-Duplex, Full-Duplex | 传输模式：单工、半双工、全双工

Simplex transmission allows data to travel in one direction only. A typical example is a keyboard sending input to a computer, or a traditional radio broadcast where the receiver cannot send data back.

单工传输只允许数据沿一个方向传输。一个典型例子是键盘向计算机发送输入，或者传统的无线电广播，接收方无法将数据发回。

Half-duplex transmission allows data to travel in both directions, but only one direction at a time. Walkie-talkies and some older Ethernet hubs use half-duplex communication: one device transmits while the other waits.

半双工传输允许数据双向传输，但一次只能一个方向。对讲机和一些较旧的以太网集线器使用半双工通信：一台设备发送时另一台设备等待。

Full-duplex transmission allows data to travel in both directions at the same time. Telephone calls, video conferencing and modern switched Ethernet connections are full-duplex, which makes them more efficient for interactive communication.

全双工传输允许数据同时双向传输。电话通话、视频会议和现代交换式以太网连接都是全双工的，这使得它们在交互通信中效率更高。

3. Serial and Parallel Transmission | 串行与并行传输

Serial transmission sends one bit at a time over a single wire or channel. It is reliable over long distances because there is less chance of interference between bits. USB, Ethernet and fibre optic links all use serial transmission.

串行传输通过单根导线或信道一次发送一位。它在长距离上更可靠，因为位之间干扰的可能性更小。USB、以太网和光纤链路都使用串行传输。

Parallel transmission sends several bits at once over multiple wires. It can be faster over very short distances, but over longer distances the bits can arrive at slightly different times, a problem called skew. It is mainly used inside computers, for example in internal data buses.

并行传输通过多根导线一次发送多个位。在很短距离内它可能更快，但在较长距离上位可能以略微不同的时间到达，这个问题称为偏移。它主要用于计算机内部，例如内部数据总线。

4. Universal Serial Bus (USB) | 通用串行总线 (USB)

Universal Serial Bus (USB) is a widely used standard for serial transmission between a computer and peripheral devices such as keyboards, mice, printers and external storage drives. USB uses twisted-pair wires for data transfer and also provides power to connected devices.

通用串行总线 (USB) 是计算机与键盘、鼠标、打印机和外部存储驱动器等外围设备之间串行传输的广泛使用标准。USB 使用双绞线进行数据传输，还为连接的设备供电。

USB supports hot-plugging, meaning devices can be connected or disconnected without switching off the computer. It is also backwards compatible, so newer USB ports can usually accept older USB devices, although the data transfer speed will be limited to the slower device.

USB 支持热插拔，这意味着设备可以在不关闭计算机的情况下连接或断开。它还具有向后兼容性，因此较新的 USB 端口通常可以接受较旧的 USB 设备，但数据传输速度将受限于较慢的设备。

5. Error Detection Methods | 错误检测方法

Errors can occur during data transmission because of electrical interference, noise or faulty hardware. Several methods are used to detect whether data has been corrupted: parity checks, checksums, echo checks and check digits. Automatic Repeat reQuest (ARQ) is a protocol that uses acknowledgements and timeouts to request retransmission when an error is detected.

数据在传输过程中可能因电气干扰、噪声或硬件故障而产生错误。可以使用几种方法来检测数据是否损坏：奇偶校验、校验和、回波校验和校验位。自动重传请求 (ARQ) 是一种协议，它使用确认和超时在检测到错误时请求重传。

A parity check adds an extra bit to each byte to make the number of 1s either even or odd. For example, the 7-bit ASCII code for ‘A’ is 1000001, which already contains two 1s, so an even parity bit would be 0. The receiver counts the 1s; if the parity is wrong, an error has occurred.

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