ABSTRACT
VBR (Variable Bit Rate) Level: 3 Definition: A quality of service (QoS) class defined by the ATM Forum for ATM networks, VBR is subdivided into a real-time (RT) class and non real-time (NRT) class. VBR (RT) is used for connections in which there is a fixed timing relationship between samples, such as with VoIP or videoconferencing. VBR (NRT) is used for connections in which there is no fixed timing relationship between samples but that still need a guaranteed quality of service. Transfer rates with VBR vary between a throughput capacity (i.e., a peak rate) and a sustained rate. However, data is not sent at a constant rate (as with CBR). (See also ABR, CBR, and UBR.)
VC (See Virtual Channel.)
V-chip Level: 1 Definition: Refers to the system that reads information encoded in a rated television program and blocks programs from the set based on the rating selected by the user (presumably the parent). Pursuant to FCC rules, half of all new television models 13 inches or larger manufactured after July 1, 1999, and all sets 13 inches or larger manufactured after January 1, 2000, must have V-chip technology. The V-chip is programmed to recognize the following ratings: TV-Y (for anyone), TV-Y7 (directed to children age 7 and above), TV-G (general audience), TV-PG (parental guidance suggested), TV-14 (suitable only for children age 14 and above), and TV-MA (suitable only for those age 17 and older). (See also Filtering.)
FIGURE V-1. Vertical blanking unit.
