📚 IGCSE Computer Science: Network Hardware Devices Exam Revision | IGCSE计算机：网络硬件设备考点归纳
A computer network is a collection of devices connected together to share data and resources. For IGCSE Computer Science (CIE 0478/0984), you need to know the purpose and function of each network hardware device, how they compare, and when to use them.
计算机网络是一组连接在一起以共享数据和资源的设备集合。在IGCSE计算机科学（CIE 0478/0984）考试中，你需要掌握每种网络硬件设备的用途和功能、它们之间的比较，以及何时使用它们。
1. Network Interface Card (NIC) and MAC Address | 网络接口卡（NIC）与MAC地址
A Network Interface Card (NIC) is a hardware component that enables a device to connect to a network. A wired NIC typically has an Ethernet port and a cable connection, while a wireless NIC uses an antenna to send and receive Wi-Fi signals. Every NIC has a unique Media Access Control (MAC) address assigned by the manufacturer.
网络接口卡（NIC）是一种使设备能够连接到网络的硬件组件。有线网卡通常带有一个以太网端口和线缆连接，而无线网卡使用天线发送和接收Wi-Fi信号。每张网卡都有一个由制造商分配的唯一介质访问控制（MAC）地址。
The MAC address is a 48-bit physical address, usually written as 12 hexadecimal digits grouped in pairs, for example 00:1A:2B:3C:4D:5E. The first 24 bits identify the manufacturer, and the last 24 bits are unique to the device. MAC addresses work at the data link layer and are used to deliver data frames within a local network.
MAC地址是一个48位的物理地址，通常写成12位十六进制数字，并成对分组，例如00:1A:2B:3C:4D:5E。前24位标识制造商，后24位对设备来说是唯一的。MAC地址工作在数据链路层，用于在本地网络内传递数据帧。
- Exam point: The NIC prepares data for transmission and converts it into electrical signals, light pulses or radio waves. 考试要点：NIC负责准备要传输的数据，并将其转换为电信号、光脉冲或无线电波。
- Exam point: A MAC address is not changed by the user and is used for communication on the LAN. 考试要点：MAC地址不会被用户改变，用于局域网内的通信。
2. MAC Address vs IP Address | MAC地址与IP地址的比较
Students often confuse MAC addresses and IP addresses. A MAC address is a physical address assigned to the NIC, while an IP address is a logical address assigned to a device on a network. Both are needed for data to reach the correct destination across the Internet.
学生经常混淆MAC地址和IP地址。MAC地址是分配给NIC的物理地址，而IP地址是分配给网络中设备的逻辑地址。数据要正确到达目的地，两者都必不可少。
| Feature 特征 | MAC Address MAC地址 | IP Address IP地址 |
|---|---|---|
| Type 类型 | Physical 物理地址 | Logical 逻辑地址 |
| Length 长度 | 48 bits 48位 | IPv4: 32 bits; IPv6: 128 bits IPv4为32位；IPv6为128位 |
| Format 格式 | 00:1A:2B:3C:4D:5E | 192.168.1.1 or 2001:0db8:… 如192.168.1.1或2001:0db8:… |
| Assigned by 分配方 | Manufacturer 制造商 | Network administrator or ISP 网络管理员或ISP |
| Changeable 是否可变 | Usually permanent 通常固定 | Can change 可以改变 |
| Layer 工作层 | Data link layer 数据链路层 | Network layer 网络层 |
| Scope 作用范围 | Local network 本地网络 | Internet-wide 全球互联网 |
Exam tip: When a data packet travels across the Internet, IP addresses are used to find the destination network. When the packet reaches that LAN, MAC addresses are used to deliver it to the correct device.
考试提示：当数据包通过互联网传输时，使用IP地址找到目标网络。当数据包到达该局域网后，使用MAC地址将其传送到正确的设备。
3. Router | 路由器
A router is a device that connects two or more networks together. It forwards data packets between different networks, such as a home LAN and the Internet, by reading the IP address in each packet and choosing the best path.
路由器是一种将两个或多个网络连接在一起的设备。它通过读取每个数据包中的IP地址并选择最佳路径，在不同网络之间转发数据包，例如在家庭局域网和互联网之间。
Routers operate at the network layer (Layer 3) and use routing tables to decide where to send data. Many modern routers also include a switch, a wireless access point and a firewall in one device.
路由器工作在网络层（第三层），并利用路由表来决定数据的发送方向。许多现代路由器还将交换机、无线接入点和防火墙集成在一个设备中。
A router can provide Network Address Translation (NAT), which allows multiple devices on a private LAN to share one public IP address when connecting to the Internet. It may also act as a DHCP server, automatically assigning IP addresses to devices.
路由器可以提供网络地址转换（NAT），允许专用局域网上的多个设备在连接互联网时共享一个公共IP地址。它还可以充当DHCP服务器，自动为设备分配IP地址。
- Router: connects different networks. 路由器：连接不同的网络。
- Switch: connects devices within the same network. 交换机：连接同一网络内的设备。
4. Switch | 交换机
A switch is a device that connects multiple devices within the same LAN, such as computers, printers and servers. It uses MAC addresses to decide which device should receive a data frame.
交换机是一种在同一局域网内连接多个设备的设备，例如计算机、打印机和服务器。它使用MAC地址来决定哪个设备应当接收数据帧。
When a switch receives a frame, it looks up the destination MAC address in its MAC address table and forwards the frame only to the correct port. This is known as unicast delivery and reduces unnecessary traffic compared with a hub.
当交换机收到一个数据帧时，它会在自己的MAC地址表中查找目的MAC地址，并将该帧仅转发到正确的端口。这被称为单播传送，与集线器相比减少了不必要的流量。
A switch learns addresses automatically as devices send data. It maintains a dynamic table that maps each MAC address to a specific port.
交换机会在设备发送数据时自动学习地址。它维护一个动态表，将每个MAC地址映射到特定端口。
Exam point: Switches are intelligent devices because they examine the destination MAC address before forwarding, unlike hubs which simply broadcast.
考试要点：交换机是智能设备，因为它在转发前会检查目的MAC地址，而不像集线器那样简单地广播。
5. Hub | 集线器
A hub is an older, simpler device that connects devices in a LAN. Unlike a switch, a hub broadcasts every incoming signal to all connected devices. The intended device accepts the data, while the others reject it but still waste resources processing it.
集线器是一种较旧、较简单的设备，用于连接局域网中的设备。与交换机不同，集线器将每个进入的信号广播给所有连接的设备。目标设备接收数据，其他设备虽然拒绝数据，但仍会浪费资源处理它。
Because all devices share the same bandwidth, collisions become more likely as more devices are connected. Modern networks use switches instead of hubs because switches provide dedicated bandwidth and reduce collisions.
由于所有设备共享相同的带宽，连接更多设备时冲突的可能性会增大。现代网络使用交换机代替集线器，因为交换机提供专用带宽并减少冲突。
Exam tip: If a question asks about a network with heavy traffic, recommend a switch, not a hub, because a switch sends data only to the intended recipient.
考试提示：如果题目问到流量很大的网络，应推荐交换机，而不是集线器，因为交换机只向目标接收者发送数据。
6. Repeater and Bridge | 中继器与网桥
A repeater is used to extend the distance of a network. It receives a weakened signal, amplifies it and retransmits it. Repeaters work at the physical layer and regenerate the signal so it can travel further without losing quality.
中继器用于延长网络的传输距离。它接收已减弱的信号，放大并重新发送。中继器工作在物理层，重新生成信号，使其能够在质量不下降的情况下传输得更远。
A bridge is a device that connects two LAN segments together. It learns the MAC addresses of devices on each segment and only forwards data packets that need to cross to the other side. This reduces traffic and improves performance.
网桥是一种将两个局域网网段连接在一起的设备。它学习每个网段上设备的MAC地址，并且只转发需要跨越到另一侧的数据包。这减少了流量并提高了性能。
Repeaters are useful in large buildings or campus networks where cable lengths exceed the maximum limit. Bridges help divide a large network into smaller collision domains.
中继器在大型建筑或校园网络中非常有用，因为线缆长度可能超过最大限制。网桥有助于将大型网络划分为更小的冲突域。
Exam tip: Do not confuse them. A repeater simply extends distance; a bridge connects two separate LAN segments and filters traffic.
考试提示：不要混淆两者。中继器仅仅是延长距离；网桥连接两个独立的网段并过滤流量。
7. Modem | 调制解调器
A modem (modulator-demodulator) converts digital signals from a computer into analog signals that can travel over telephone lines or cable systems. It also converts incoming analog signals back into digital signals.
调制解调器（modem，调制器-解调器）将计算机的数字信号转换成可以沿电话线或有线电视系统传输的模拟信号。它还将收到的模拟信号转换回数字信号。
This conversion is necessary because traditional telephone lines carry analog signals, while computers process digital signals. Fibre broadband still requires a modem or optical network terminal (ONT) to connect the ISP’s line to your router.
这种转换是必需的，因为传统电话线传输模拟信号，而计算机处理数字信号。光纤宽带仍然需要调制解调器或光网络终端（ONT）来将ISP的线路连接到路由器。
Do not confuse a modem with a router. A modem connects a home network to the Internet service provider; a router connects different networks together.
不要把调制解调器和路由器混淆。调制解调器将家庭网络连接到互联网服务提供商；路由器则将不同的网络连接在一起。
8. Wireless Access Point (WAP) | 无线接入点
A Wireless Access Point (WAP) allows wireless devices such as laptops, smartphones and tablets to connect to a wired network using Wi-Fi. It acts as a bridge between the wireless and wired parts of a network.
无线
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