Vertical service code

A vertical service code (VSC) is a sequence of digits and the signals <a href="/facts/Asterisk/qwmtPW5V">star</a> (*) and <a href="/facts/Number_sign/bHYCsWs1">pound/hash</a> (#) dialed on a <a href="/facts/Telephone_keypad/lJWSa85A">telephone keypad</a> or <a href="/facts/Rotary_dial/Jrlloo2h">rotary dial</a> to access certain telephone service features. Some vertical service codes require dialing of a <a href="/facts/Telephone_number/Px4q5qFo">telephone number</a> after the code sequence. On a <a href="/facts/Touch_tone/vg5vFo0X">touch tone</a> telephone, the codes are usually initiated with the <a href="/facts/Asterisk/qwmtPW5V">star key</a>, resulting in the commonly used name star codes. On rotary dial telephones, the star is replaced by dialing 11.
In <a href="/facts/North_American/djNjCQIl">North American</a> <a href="/facts/Telephony/2GwTTepw">telephony</a>, VSCs were developed by the <a href="/facts/American_Telephone_and_Telegraph_Company/BfsX7eX2">American Telephone and Telegraph Company</a> (AT&T) 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 <a href="/facts/North_American_Numbering_Plan_Administration/0QQ8v3ph">North American Numbering Plan Administration</a>. 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 telephone subscriber, going up (vertically) inside the local <a href="/facts/Telephone_exchange/PaRpGm8I">central office</a> instead of out (horizontally) to another telephone company.

Vertical service code open-in-new

Vertical service code