📚 4 Network Hardware | 网络硬件
Network hardware is the physical equipment that allows computers and other digital devices to connect, communicate and share information across a network. These devices transmit, receive, forward and control data signals. For IGCSE Science and Computer Science students, network hardware is a core topic because it explains how the internet and local networks actually work in everyday life.
网络硬件是让计算机和其他数字设备能够连接、通信并共享信息的物理设备。这些设备负责发送、接收、转发和控制数据信号。对 IGCSE 科学与计算机科学学生来说，网络硬件是核心主题，因为它解释了互联网和局域网在现实生活中是如何工作的。
Network hardware can be divided into active and passive devices. Active devices, such as routers and switches, make decisions about where data should go. Passive devices, such as cables and patch panels, only provide physical pathways and do not change the data. Understanding this difference helps students design and describe simple networks accurately.
网络硬件可分为有源设备和无源设备。路由器、交换机等有源设备会决定数据的去向；电缆、配线架等无源设备只提供物理通道，不改变数据。理解这一区别有助于学生准确地设计和描述简单网络。
1. What Is Network Hardware? | 什么是网络硬件
Network hardware refers to the physical components used to build a computer network. Examples include network interface cards, switches, routers, wireless access points, modems and the cables that connect them. Each piece of hardware performs a specific job in moving data from one device to another.
网络硬件是指用于构建计算机网络的物理组件。例子包括网络接口卡、交换机、路由器、无线接入点、调制解调器以及连接它们的电缆。每种硬件在将数据从一台设备传输到另一台设备时都执行特定的任务。
In a typical network, hardware works together in layers. A computer first uses its network interface card to send data. A switch forwards the data within the local network, and a router sends it to other networks. A modem converts the signal for transmission to the internet service provider.
在典型网络中，硬件分层协同工作。计算机首先使用网络接口卡发送数据。交换机在局域网内转发数据，路由器将数据发送到其他网络。调制解调器则转换信号，以便传输给互联网服务提供商。
2. Network Interface Card (NIC) | 网络接口卡
A network interface card, or NIC, is the hardware component that connects a computer to a network. It can be built into the motherboard or added as a separate expansion card. The NIC converts digital data from the computer into electrical, optical or radio signals suitable for the network medium.
网络接口卡（NIC）是计算机连接网络的硬件部件。它可以集成在主板上，也可以作为独立扩展卡安装。NIC 将计算机的数字数据转换为适合网络介质的电信号、光信号或无线电信号。
Each NIC has a unique MAC address assigned by the manufacturer. This address is stored in the card's firmware and is used to identify the device on a local network. A wireless NIC performs the same role as a wired NIC, but it uses radio waves to transmit and receive data.
每块 NIC 都有制造商分配的唯一 MAC 地址。该地址存储在网卡固件中，用于在局域网内标识设备。无线网卡的作用与有线网卡相同，但它使用无线电波来发送和接收数据。
3. MAC Addresses and Identification | MAC 地址与设备识别
A MAC address is a 48-bit identifier usually written as six pairs of hexadecimal digits, for example 00:1A:2B:3C:4D:5E. The first half identifies the manufacturer, and the second half is unique to the device. This address operates at Layer 2 of the OSI model.
MAC 地址是一个 48 位标识符，通常写成六组十六进制数，例如 00:1A:2B:3C:4D:5E。前半部分标识制造商，后半部分在设备中唯一。它工作在 OSI 模型的第 2 层。
Switches use MAC addresses to forward frames only to the correct destination. Unlike IP addresses, MAC addresses do not normally change when a device moves between different networks; they remain tied to the NIC itself. This is why MAC addresses are useful for identifying physical devices.
交换机利用 MAC 地址将帧只转发到正确的目的地。与 IP 地址不同，设备在不同网络之间移动时 MAC 地址通常不会改变；它始终与网卡本身绑定。这就是 MAC 地址可用于识别物理设备的原因。
4. Hubs and Repeaters | 集线器与中继器
A hub is a simple hardware device that connects several Ethernet devices together. When a hub receives a data packet on one port, it repeats that packet to all other ports. This creates unnecessary traffic and increases the chance of data collisions.
集线器是一种连接多台以太网设备的简单硬件。当集线器在一个端口收到数据包时，会将该数据包重复发送到所有其他端口。这会产生不必要的流量，并增加数据冲突的可能性。
A repeater is even simpler: it receives a weakened signal and regenerates it at full strength so the signal can travel a longer distance. Repeaters do not read addresses or filter data; they only boost the signal. Hubs are now largely replaced by switches because hubs share bandwidth among all ports and operate in half-duplex mode.
中继器更简单：它接收衰减的信号，并以完整强度重新生成信号，使信号能够传输更远的距离。中继器不读取地址，也不过滤数据，只增强信号。集线器如今基本已被交换机取代，因为集线器在所有端口之间共享带宽，并且工作在半双工模式。
5. Switches: Intelligent Forwarding | 交换机：智能转发
A switch is a networking device that connects devices within the same local area network. Unlike a hub, a switch learns the MAC address of each connected device and builds a MAC address table. It then forwards an incoming frame only to the port where the destination device is connected.
交换机是在同一局域网内连接设备的网络设备。与集线器不同，交换机会学习每台连接设备的 MAC 地址并建立 MAC 地址表。然后，它只将收到的帧转发到目标设备所连接的端口。
This forwarding method greatly reduces unnecessary traffic and allows full-duplex communication, meaning devices can send and receive data at the same time. Switches therefore increase network efficiency and are essential in modern wired networks.
这种转发方式大大减少了不必要的流量，并支持全双工通信，即设备可以同时发送和接收数据。因此，交换机提高了网络效率，是现代有线网络不可或缺的设备。
Exam questions often ask students to explain why a switch is better than a hub. The key points are reduced collisions, dedicated bandwidth per port, and the ability to learn MAC addresses.
考题常要求学生解释为什么交换机优于集线器。关键点是减少冲突、每个端口拥有专用带宽，以及能够学习 MAC 地址。
6. Routers and Gateway Functions | 路由器与网关功能
A router connects different networks together, such as a home LAN and the internet. It forwards data packets based on IP addresses and uses routing tables to choose the best path. A router can also perform Network Address Translation (NAT), allowing many private IP addresses to share one public IP address.
路由器将不同网络连接在一起，例如家庭局域网和互联网。它根据 IP 地址转发数据包，并使用路由表选择最佳路径。路由器还能执行网络地址转换（NAT），让多个私有 IP 地址共享一个公共 IP 地址。
A router often acts as a gateway, the device that sits at the boundary of a network. When a computer wants to send data to a device outside its local network, it sends the packet to the default gateway, which is usually the router.
路由器通常充当网关，即位于网络边界的设备。当计算机要向局域网之外的设备发送数据时，它会将数据包发送到默认网关，这通常是路由器。
Routers operate at Layer 3 of the OSI model because they inspect IP addresses, not MAC addresses. This allows them to connect networks that use different Layer 2 technologies.
路由器工作在 OSI 模型的第 3 层，因为它检查的是 IP 地址而不是 MAC 地址。这使得路由器能够连接使用不同第 2 层技术的网络。
7. Wireless Access Points | 无线接入点
A wireless access point (WAP) allows wireless devices to connect to a wired network. It converts data frames between wired Ethernet and wireless radio signals. In a home network, the router often includes a built-in access point, but larger businesses use separate WAPs to extend coverage.
无线接入点（WAP）允许无线设备连接到有线网络。它在有线以太网和无线无线电信号之间转换数据帧。在家庭网络中，路由器通常内置接入点，但大型企业会使用独立的 WAP 来扩大覆盖范围。
A WAP broadcasts an SSID (service set identifier), which is the network name users see on their devices. Modern access points support Wi-Fi standards such as 802.11ac and 802.11ax, offering higher speeds and better handling of many devices.
WAP 广播 SSID（服务集标识符），也就是用户在设备上看到的网络名称。现代接入点支持 802.11ac 和 802.11ax 等 Wi-Fi 标准，提供更高的速度，并能更好地处理多台设备。
Security is important for wireless networks. WAPs should use encryption such as WPA2 or WPA3 to protect data, because wireless signals can be intercepted by nearby devices.
无线网络的安全性很重要。WAP 应使用 WPA2 或 WPA3 等加密来保护数据，因为无线信号可能被附近的设备截获。
8. Modems and Internet Connection | 调制解调器与互联网连接
A modem (modulator-demodulator) converts digital signals from a computer into a form suitable for transmission over telephone lines, cable systems or fibre. At the receiving end, another modem converts the signal back into digital data.
调制解调器（modem，调制-解调器）将计算机的数字信号转换为适合通过电话线、有线电视系统或光纤传输的形式。在接收端，另一个调制解调器将信号转换回数字数据。
In many home networks, the modem connects to the internet service provider (ISP), and a separate router or combined modem-router provides local network functions. Fibre connections may use an ONT (optical network terminal) instead of a traditional modem.
在许多家庭网络中，调制解调器连接到互联网服务提供商（ISP），而独立路由器或调制解调器-路由器组合提供局域网功能。光纤连接可能使用 ONT（光网络终端）而不是传统调制解调器。
The key difference between a modem and a router is that a modem brings the internet connection into the building, while a router distributes that connection to multiple devices and routes traffic between them and the internet.
调制解调器和路由器的关键区别在于，调制解调器将互联网连接引入建筑物，而路由器将该连接分配给多个设备，并在它们与互联网之间路由流量。
9. Transmission Media: Copper, Fibre and Wireless | 传输介质：铜缆、光纤与无线
Network hardware also includes the physical media through which data travels. Twisted-pair copper cables, such as Cat5e and Cat6, are common in LANs. They carry electrical signals, are inexpensive and easy to install, but suffer from interference and limited distance.
网络硬件还包括数据传输经过的物理介质。双绞铜缆（如 Cat5e 和 Cat6）在局域网中很常见。它们传输电信号，价格便宜且易于安装，但会受到干扰并受距离限制。
Fibre-optic cables carry data as light pulses through glass or plastic fibres. They offer very high bandwidth, low attenuation and immunity to electromagnetic interference, making them suitable for long-distance and high-speed links.
光纤电缆通过玻璃或塑料纤维以光脉冲传输数据。它们提供非常高的带宽、低衰减且不受电磁干扰，因此适合长距离和高速链路。
Wireless media use radio waves or infrared. Wireless is flexible and supports mobility, but its speed and reliability can be affected by distance, walls, interference and the number of connected devices.
无线介质使用无线电波或红外线。无线方式灵活并支持移动性，但其速度和可靠性会受到距离、墙壁、干扰以及连接设备数量的影响。
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