Repeaters.
Repeaters are the most basic type of active network equipment. They operate solely at the physical layer, receiving a signal on one port, or connection, and rebroadcasting it on all of its other ports. They can extend a network beyond the limits imposed by the wiring by boosting the signal level.

Most advertisements for "hubs" are referring to multiport repeaters.
They usually come with a number of ports that are multiples of 12 and allow the network to support up to that number of workstations. Some hubs are stackable, which means they have a special connector that allows a district to easily connect more than one hub together. Others come as chassis systems for which support additional cards, each card having another 12 ports.

Switches.
Switches are an advanced form of repeaters. They also act at the physical level by repeating the signal. Unlike repeaters that repeat an incoming packet out all of its ports, a switch looks at the destination of the packet and only sends it to the port of the destination.  This can reduce excess traffic on a network since it isolates each port and send fewer packets to each port, thereby reducing collisions and increasing the performance of the network.

Bridges.
Bridges operate at a higher level than repeaters, working at the data link layer and looking at the actual packets that are on the network. When they receive a packet, they store the entire packet in memory, verify its correctness, and retransmit it on the correct port. This allows them to connect different types of Ethernet networks together such as a 10baseT and a coax network. They also reset the "3-4-5 rule" for each port, making each port its own network. This is because it stores the entire packet and rebroadcasts it, isolating each port from the others. Like switches, they look at the destination of the packet and only send it to the port where the destination is located, reducing traffic on the network.

Routers.
Routers operate at the network level. They receive a packet, view its destination, and determine if the packet is destined for a network that is directly connected to the router or if it is destined for a network further away. If it is the first it sends the packet to the correct port. If it is the latter, it sends the packet to the next router along the path to the packet's final destination. For this reason, routers typically connect between a LAN and a WAN to limit the traffic on the WAN to only packets that need to cross it. Additionally, because routers look at the network information from a packet, they can convert between different network protocols.

NICs.
The network interface card (NIC) is an add-on board that serves as the connection between the client computer and the network infrastructure. In other words, to hook all your computers together, a special electronic circuit card called a NIC goes inside each computer. That's where you plug in the cable that connects the computer to the network. Some computers come with built-in network interfaces and do not require an additional NIC. You will find that NICs vary in cost depending on the type of protocol they support. For example, 10BaseT NICs are inexpensive when compared to FDDI NICs.

Cables.
Unshielded twisted pair (UTP) wire.
Unshielded twisted pairhas been used by telephone companies for years to attach phones for local service. Today it is used not only for voice applications, but also in data-network applications. Because of the use of UTP in data communications, seven specifications have emerged, ranging from Category 1 for voice grade to Category 7 for ultrahigh-speed data. Today's EIA/TIA standard is to use Category 5 UTP for LANs. Category 5 UTP has four distinct twisted pairs of wire within an outer sheath. This wire can handle data transfer rates in excess of 155 Mbps (megabits per second) and is likely to be supported for many years to come. It has become the most common media type for LANs today.

Fiber optic cable.
Fiber optic cableuses light instead of electricity to carry data. This accounts for two of its advantages: (1) Data can be moved at extremely high speeds without generating interfering RF (radio frequency) signals and (2) Data transmission is not affected by the proximity of electrical equipment or high-voltage transmission. Most fibers are made of glass, plastic, or plastic-clad glass. The fibers are somewhat flexible, and the degree of flexibility depends on the fiber diameter. There are three components to optical fiber: the core, the cladding, and the coating. The cladding blocks exterior light sources and restricts the internal light to the core only. The coating is usually plastic and surrounds the cladding. Its purpose is to protect the fiber from physical and environmental damage.

There are two categories of fiber: single mode and multimode.
Single-mode fiber has a smaller diameter core, generally uses laser as a light source, and can transmit data in excess of 25 miles without having to regenerate the signal.

Multimode fiber has a larger diameter core, generally uses low-cost, light-emitting diodes as a light source, and can transmit data up to a mile. LANs and campus networks usually make use of multimode fiber. Both categories of fiber are generally much more expensive than twisted pair wire. Because of this, fiber is usually limited to situations where long distance runs or very high speeds are needed.

Coaxial cable.
Coaxial cable is probably the most well-known type of cable. The term coaxial denotes a class of cable that has several layers of material surrounding a common axis. A center conductor, either solid or stranded, is surrounded by a nonconductive material, covered by a shielding material, then covered by an abrasion-resistant jacket. At one time, coaxial cable was the only media available for use in data networking. Today, the most common use of coaxial cable is for video distribution, while UTP and fiber are commonly used in data networking.

Wireless media.
Several new technologies allow for the use of radio or microwave transmission for data networks. Wireless systems have special applications in interbuilding communication and might be useful in your campus or district networks. Be aware that there are trade-offs with wireless. Reliability, cost, and performance should be carefully analyzed.