In North American telephony, a vertical service code or VSC is a special code dialed prior to a telephone number that engages some type of special telephone service.
Typically preceded with an asterisk, or * (star), key on the touch tone keypad and colloquially referred to as star codes, most are two digits in length although, as more services are developed, those that use 2 or 3 as the first digit are sometimes three digits in length.
Developed by AT&T as Custom Local Area Signaling Services or CLASS codes (or LASS) in the 1960s and 70's, their use became ubiquitous throughout the 1990s and eventually became a recognized standard. As CLASS was an AT&T trademark, the moniker of Vertical service codes was adopted by the North American Numbering Plan Administration. The use of the word "vertical" is a somewhat arcane tip of the hat to older switching methods and the fact that these services can only be accessed by a local telephone subscriber; going up (or vertically) inside the local central office instead of out to another telephone company.
Contents |
|
