A television network or television broadcaster is a telecommunications network for distribution of television program content, where a central operation provides programming to many television stations or pay television providers. Until the mid-1980s, television programming in most countries of the world was dominated by a small number of terrestrial networks. Many early television networks (such as NBC, the ABC, or the BBC) evolved from earlier radio networks. Overview In countries where most networks broadcast identical, centrally originated content to all of their stations and where most individual television transmitters therefore operate only as large "repeater stations", the terms "television network", "television channel" (a numeric identifier or radio frequency) and "television station" have become mostly interchangeable in everyday language, with professionals in television-related occupations continuing to make a differentiation between them. Within the industry, a tiering is sometimes created among groups of networks based on whether their programming is simultaneously originated from a central point, and whether the network master control has the technical and administrative capability to take over the programming of their affiliates in real-time when it deems this necessary – the most common example being during national breaking news events. In North America in particular, many television networks available via cable and satellite television are branded as "channels" because they are somewhat different from traditional networks in the sense defined above, as they are singular operations – they have no affiliates or component stations, but instead are distributed to the public via cable or direct-broadcast satellite providers. Such networks are commonly referred to by terms such as "specialty channels" in Canada or "cable networks" in the U.S. A network may or may not produce all of its own programming. If not, production companies (such as Warner Bros. Television, Universal Television, Sony Pictures Television and TriStar Television) can distribute their content to the various networks, and it is common that a certain production firm may have programs that air on two or more rival networks. Similarly, some networks may import television programs from other countries, or use archived programming to help complement their schedules. Some stations have the capability to interrupt the network through the local insertion of television commercials, station identifications and emergency alerts. Others completely break away from the network for their own programming, a method known as regional variation. This is common where small networks are members of larger networks. The majority of commercial television stations