Vertical service code: Difference between revisions

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{{Globalize|article|USA|2name=the United States|date=December 2019}}

A '''vertical service code''' ('''VSC''') is a sequence of digits and the signals [[asterisk|star]] (*) and number sign (#) dialed on a [[telephone keypad]] or [[rotary dial]] to enable or disable certain telephone service features.<ref name=":0" /> Some vertical service codes require dialing of a [[telephone number]] after the code sequence. On a [[touch tone]] telephone, the codes are usually initiated with the [[Asterisk#Telephony|star key]], resulting in the commonly used name ''star codes''. On rotary dial telephones, the star is replaced by dialing ''11''.

In [[North American]] [[telephony]], VSCs were developed by [[AT&T Corp.]] as '''Custom Local Area Signaling Services''' ('''CLASS''' or '''LASS''') codes 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 ''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 (''vertically'') inside the local [[telephone exchange|central office]] instead of out (''horizontally'') to another telephone company.

==Feature definitions ==