Vertical service code
A vertical service code (VSC) is a special code dialed prior to (or instead of) a telephone number that engages some type of special telephone service or feature.
Contents
Description
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; as more services are developed, those that use 2 or 3 as the first digit are sometimes three digits in length.
History
In North American telephony, VSCs were developed by AT&T Corp. as Custom Local Area Signaling Services or CLASS codes (sometimes LASS) in the 1960s and 70s.
Their use became ubiquitous throughout the 1990s and eventually became a recognized standard.
As CLASS was an AT&T trademark, the term "vertical service code" was adopted by the North American Numbering Plan Administration.
The use of the word "vertical" is a somewhat dated reference 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 (or horizontally) to another telephone company.
See also
- Mobile dial code
- Pat Fleet – Prompt voice for most U.S. AT&T implementations of VSC features
- Public switched telephone network
- Signalling System 7
- Telephony
External links
- Vertical service code @ Wikipedia
