Computer Networking has a physical component that is overlaid by the topology describing the way that network nodes are interconnected. The topology of a network is described by diagrams that use symbols denoting network nodes and network links.
The media used to interconnect devices that form a computer network may be:
- Electrical cable
- Optical fiber
- Radio waves
- Infrared signals
The first two categories define the “wired technologies” used in computer networking, while the last two are known as “wireless technologies”.
The following four categories are the best known and used to set up computer networks:
- Twisted pair wire – It is maybe the most used medium, but also the slowest of all. It consists of pairs of twisted insulated copper wires that can be either unshielded or shielded. The transmission speeds may range from 2 Mbps to 10 Mbps.
- Coaxial cable – It is an aluminum or copper wire included in an insulated layer of material with a high dielectric constant. The whole thing is wrapped in a conductive layer. The insulation is designed to minimize distortion and interference. Transmission speeds range from 200 Mbps to 500 Mbps.
- Optical fiber – It is in fact glass fiber that uses light pulses to transmit data. Unlike metal wires, fiber glass is immune to electrical interference and has lower transmission loss. Moreover, optical fibers can carry several wavelengths of light simultaneously, increasing the rate at which information can be sent. Speeds can reach trillions of bits per second. Optical fibers are also used to interconnect continents through undersea cables.
Computer networking based on wireless technologies does not use physical media to transmit signals, but does require relay stations to retransmit the signal if long distances have to be covered.
- Terrestrial microwaves – They use Earth-based receivers and transmitters. These waves are situated in the low-gigahertz range, and, therefore, communications are limited to line-of-sight. Relays are situated at approximately every 48 km.
- Communications satellites – They use microwave radio waves to communicate. These waves are not deflected by the atmosphere of the Earth. The satellites are placed in space, on a geosynchronous orbit at 35,400 km above the equator. They can receive and relay data, voice, and TV signals.
- Radio technologies – They use high-frequency and low-frequency radio signals to transmit data. They enable communications between several devices in a restrained area.
- Cellular and PCS systems – They divide a region into multiple geographic areas and use multiple radio communications technologies. Each area has a radio relay antenna or a low-power transmitter to direct calls from one area to another.
- Free-space optical communication – Another system used in computer networking, working with invisible or visible light, it is usually limited at line-of-sight propagation.