Networks are systems that are formed by links. For example, roads that connect groups of people together create a physical network. Connections with your friends create your personal network. Websites that allow individuals to link to each other’s pages are called social networking sites.
People use the following networks every day:
- Mail delivery system
- Telephone system
- Public transportation system The public transportation system shown in the figure is similar to a computer network. The cars, trucks, and other vehicles are like the messages that travel within the network. Each driver defines a starting point (source computer) and an ending point (destination computer). Within this system there are rules, similar to stop signs and traffic lights, which control the flow from the source to the destination.
Computer networks consist of a variety of devices. Some devices can serve either as hosts or peripherals. A host is any device that sends and receives information on the network. A printer connected to your laptop is a peripheral. If the printer is connected directly to a network, it is acting as a host.
Many different types of host devices can connect to a network. Some of the more common ones are shown in Figure .
Note: An Internet Protocol phone, which is known as an IP phone, connects to a computer network instead of the traditional telephone network. Computer networks are used in businesses, homes, schools, and government agencies. Many networks are connected to each other through the Internet. A network can share many different types of resources .
Computer networks contain many devices that exist in between the host devices. These intermediary devices ensure that data flows from one host device to another host device. The most common intermediary devices are shown in the figure.
A switch is used to connect multiple devices to the network. A router is used to forward traffic between networks. A wireless router connects multiple wireless devices to the network. In addition, a wireless router often includes a switch so that multiple wired devices can connect to the network. An access point (AP) provides wireless connectivity, but has fewer features than a wireless router. A modem is used to connect a home or small office to the Internet.
Communication across a network is carried on a medium. The medium provides the channel over which the message travels from source to destination. The plural for medium is media.
Network devices are linked together using a variety of media. As shown in Figure 1, these media are:
- Copper cabling – Uses electrical signals to transmit data between devices
- Fiber-optic cabling – Uses glass or plastic fiber to carry information as light .
- Wireless connection – Uses radio signals, infrared technology, or satellite transmissions Local area network (LANs), wide area networks (WANs), and wireless networks are discussed in the next topic. The Cloud will be used throughout this course to represent connections to the Internet. The Internet is often the medium for communications between one network and another network.