Virtual channel

In most telecommunications organizations, a virtual channel is a method of remapping the program number as used in H.222 Program Association Tables and Program Mapping Tables to a channel number that can be entered via digits on a receiver's remote control.

A "virtual channel" was first used for DigiCipher 2 in North America and then later used and referred to as a logical channel number (LCN) for private European Digital Video Broadcasting extensions widely used by the NDS Group and NorDig in other markets.

Pay television operators were the first to use either of these systems as a method of channel reassignment and/or rearrangement that suited their need to group multiple channels by their content or origin as well as to a lesser extent to localize advertising to a particular market.

Free-to-air ATSC uses the DigiCipher 2 method to maintain the same radio frequency channel allocation that the NTSC channel was using when both were simulcasting so the same number could bring up either service.

Virtual circuit

A virtual circuit (VC) is a mean of transporting data over a packet switched computer network in such a way that it appears as though there is a dedicated physical layer link between the source and destination end systems of this data. The term virtual circuit is synonymous with virtual connection and virtual channel. Before a connection or virtual circuit may be used, it has to be established, between two or more nodes or software applications, by configuring the relevant parts of the interconnecting network. After that, a bit stream or byte stream may be delivered between the nodes; hence, a virtual circuit protocol allows higher level protocols to avoid dealing with the division of data into segments, packets, or frames.

Virtual circuit communication resembles circuit switching, since both are connection oriented, meaning that in both cases data is delivered in correct order, and signalling overhead is required during a connection establishment phase. However, circuit switching provides a constant bit rate and latency, while these may vary in a virtual circuit service due to factors such as: