A modem connects your local network to an internet service provider (ISP), a switch connects devices within the same local network, and a router directs data between different networks. This topic is shared by SL and HL students.
| Device | Main function | Address or signal used |
|---|---|---|
| Modem | Converts or translates signals so data can travel between the ISP's connection and the customer's network equipment | Cable, fibre, DSL, or mobile-network signalling |
| Switch | Forwards data to the correct device within a local area network (LAN) | MAC addresses |
| Router | Forwards data packets between networks, such as a home LAN and the internet | IP addresses |
A switch learns which MAC addresses are connected to its ports. When it receives an Ethernet frame, it sends that frame through the port leading to the intended device, reducing unnecessary traffic within the LAN.
A router examines the destination IP address of a packet and selects a route towards another network. Home routers often also provide DHCP, network address translation, firewall functions, Wi-Fi, and built-in Ethernet switch ports. However, these additional functions are not what defines a router.
A modem handles the connection technology used by the ISP. For example, a cable modem translates between signals on a coaxial cable and data usable by a router. Some fibre connections use an optical network terminal instead of a device commonly called a modem.
A common misconception is that these devices are interchangeable because one household box may perform all three functions. They remain logically distinct: the modem provides the ISP link, the router connects networks, and the switch connects devices inside one network.
For IB Digital Society, this relates to 3.4 Networks and the internet, particularly network components and characteristics. In an exam response, identify each device's distinct function and use precise terms such as LAN, frame, packet, MAC address, and IP address. Avoid defining a router only as “the box that provides Wi-Fi.”
