Network devices, or network equipment, are fundamental components of computer networks. The first network devices typically encountered by those new to the study of computer networks are hubs, switches, bridges, and modems.

Hub

A hub is a network device that connects multiple hosts, as many as there are available ports. A hub generally consists of a few ports. Referring to the ISO/OSI stack, which is the conceptual framework for studying networks, hubs are Level 1 (L1) devices, since network traffic arriving from one port is forwarded to all other ports, occupying the transmission channel not only of the receiving node but also of other nodes. This is a major flaw of hubs, and in fact, technological evolution has meant that they are no longer used. that they are now obsolete devices.

Switches

Hubs have been completely replaced by switches, which in current configurations are currently produced with a large number of ports: at least 8 ports for home use, up to 24 or 48 ports for business use.

Switches, during their operation, are able to self-learn which host is connected to a certain port, thus overcoming the limitation of hubs, which was to repeat traffic from a port on all connected ports.

Switches, which are Layer 2 (L2) devices, are characterized by the fact that network traffic arriving from a port is forwarded only to the recipient's port. In this way, the network is effectively divided into independent segments according to a star topology: imagine that node C wants to communicate with node D during communication between A and B. Not only is this communication possible, but it is also possible to communicate with node D. This is possible, but it will occur without any collisions within the network.

Bridge

The bridge is also an L2 device, primarily used to connect segments of two different networks, such as two LANs (Local Area Networks), which, when connected via the bridge, become an extended LAN. Today, the use of the bridge remains valid as a theoretical concept, but the bridge's functionality is still achieved through switches, connecting the two LANs in point-to-point mode. Bridges forward data "intelligently," meaning they forward traffic to the other segment only if it is directed to a host on that segment.

Modem

The modem is a hardware device that allows an end node to connect to a network using the telephone line. Terminal nodes use
digital signals, while the telephone line uses analog signals: the modem converts between these two types of signals. Specifically, the modem:

• converts the PC's digital signal to analog (modulation) when the computer sends data over the network;
• converts the telephone line's analog signal to digital (demodulation) when the computer receives data.