We can watch videos on smartphones and send messages to friends because computers around the world are connected through a “network.” In this lesson, you will learn about types of networks, the roles of network devices, and an important system called “packet switching” that supports the Internet.
LANs, WANs, and the Internet
A network within a limited area, such as a home or school, is called a LAN (Local Area Network). A wide-area network that connects LANs at distant locations through communication lines is called a WAN (Wide Area Network). The huge “network of networks” created by interconnecting networks around the world is the Internet. From home, you connect to the Internet by signing a contract with an ISP (Internet Service Provider).
Devices That Connect Networks
・Hub: A concentrator that connects multiple devices with cables within a LAN.
・Router: A device that relays communication between different networks and performs route selection (routing). It serves as the gateway between a home LAN and the Internet.
・Access point: A device that connects devices by radio waves using Wi-Fi (wireless LAN).
Client-Server and Peer-to-Peer Systems
There are two ways to divide the roles of computers on a network. In a client-server system, roles are divided between a server that provides services and a client that requests services. Many services, including websites and email, use this system. In contrast, a peer-to-peer (P2P) system does not use a dedicated server; computers communicate directly with one another on an equal basis.
Circuit Switching and Packet Switching
Traditional landline telephones used circuit switching, in which the line to the other party was exclusively occupied during a call. In contrast, the Internet uses packet switching. Data is divided into small units called packets. A header, including the destination and sequence number, is attached to each packet. The packets are then sent and reassembled in their original order on the receiving side.
The advantages of packet switching are: ① a single line can be shared by multiple communications, resulting in high line utilization efficiency; ② even if part of a route fails, data can be diverted through another route, making the system resistant to failures; and ③ even when an error occurs, only the lost packets need to be sent again.
- LAN = local network, WAN = wide-area network, Internet = an interconnected network of networks.
- A router relays communication between different networks and selects routes. A hub is a concentrator within a LAN.
- A client-server system divides roles, while a P2P system treats computers as equals.
- Packet switching sends data in small units. It is efficient and resistant to failures.
Practice Questions
- Explain the difference between a LAN and a WAN.
- Explain the role of a router.
- Give two advantages of packet switching over circuit switching.
Answers and Explanations
- Answer: A LAN is a network within a limited area, such as a home, school, or office. A WAN is a wide-area network that connects LANs at distant locations through communication lines.
Explanation: They are distinguished by the size of the area they cover. The Internet is created by interconnecting networks around the world. - Answer: It relays communication between different networks and examines packet destinations to select and forward packets along the best routes (routing).
Explanation: In a home, it serves as the gateway between the LAN and the Internet. - Answer: ① Because a line can be shared by multiple communications, its utilization efficiency is high. ② Even if part of a route fails, data can be diverted through another route, making the system resistant to failures.
Explanation: “Error handling is efficient because only lost packets need to be sent again” is also correct. Circuit switching exclusively occupies the line throughout a call.