A television network is a telecommunications network for distribution of television content, whereby a central operation provides programming to many television stations or pay TV providers. Until the mid-1980s, television programming in most countries of the world was dominated by a small number of broadcast networks. Many early television networks (e.g. the BBC, NBC or CBS) evolved from earlier radio networks.
In countries where most networks broadcast identical, centrally originated content to all their stations and where most individual TV 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 TV-related occupations continuing to make a difference 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 breaking national 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 than 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 headends or direct-broadcast satellite companies. 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 houses such as Warner Bros. and Sony Pictures can distribute their content to the different networks, and it is common that a certain production house may have programmes on two or more rival networks. Similarly, some networks may import television programmes from other countries, or use archival programming to help complement their schedules.
Some stations or headends have the capability to interrupt the network through the local insertion of TV commercials, station IDs, and emergency alerts. Others completely break away from the network for their own programming, known as regional variation. This is common where small networks are members of larger networks.
As with individual stations and headends, modern network operations centers usually use broadcast automation to handle most tasks. These systems are not only used for scheduling and for playout from video servers, but use exact atomic time from GPS or other sources to maintain perfect synchronization with upstream and downstream systems, so that programming appears seamless to viewers.
