Telecommunication networks are a collection of telecommunications links, switching nodes, and users who communicate with one another through these interconnected nodes. They are used for telecommunication (which is the transmission of information across distances) such as voice, video, text, or data. The nodes in the network are generally called switches or nodes—but they can also be other devices like modems, routers, multiplexers, and exchanges. The links between them connect the nodes and usually refer to the physical cables, optical fibers, and radio waves that carry the information between those nodes. The communications channels are required for every individual user to establish a connection from their terminal to the node that they wish to communicate with; each link of each user is called a communications channel.