Communication Networks and Internet Technologies: notes

Networks

A network is two or more computers linked to share data, devices (like a printer) and an internet connection.

• LAN (local area network): one building or school.
• WAN (wide area network): across towns or countries. The internet is the biggest WAN.
• MAN (metropolitan area network): one city.
• PAN (personal area network): devices around one person, often by Bluetooth.

Topologies

• Star: every device connects to a central switch. One cable failing affects one device only; the switch failing stops all.
• Bus: all devices share one backbone cable with terminators at each end. Cheap, but a break stops the network.
• Ring: each device connects to two others in a circle; data travels one way.
• Mesh: devices have many links, so data can take another route if one fails.

Transmission

• Simplex: one direction only (radio broadcast). Half duplex: both ways but one at a time (walkie-talkie). Full duplex: both ways at once (phone call).
• Media: twisted pair cable, coaxial cable, fibre optic (fast, long distance, light signals), and wireless (Wi-Fi, Bluetooth, microwave, satellite).
• Mobile technology: phones reach the internet over 3G, 4G and 5G networks, and share data by Bluetooth or a hotspot.

Devices

• Switch: joins devices in a LAN and sends data only to the right one.
• Router: joins different networks and picks the route, for example a LAN to the internet.
• Modem: converts digital signals to analogue and back for a phone line.
• NIC (network interface card): lets a computer join a network; it has a unique MAC address.

Internet

• An ISP (Internet Service Provider), such as Liquid or TelOne, connects you to the internet.
• Services: the World Wide Web, email, file transfer, video calls, cloud storage.
• Protocols are agreed rules: HTTP/HTTPS (web pages), FTP (file transfer), SMTP and POP3/IMAP (email), TCP/IP (sending data across the internet).
• Cloud services store files and run software on remote servers you reach over the internet.