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Custom Local Area Signaling Services

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Title: Custom Local Area Signaling Services  
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Subject: Intelligent Network, Caller ID, Automatic number identification, Local number portability, Analog Display Services Interface, Call Waiting Deluxe, CLASS
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Custom Local Area Signaling Services

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. 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.

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.

List of vertical service codes

The following are the VSCs generally used in the North American Numbering Plan. Not all of these services are available in all areas, and some are only available to landline or cellular telephones. Some require additional services be purchased from the telephone company to use them.

Local Area Signalling Services (LASS) and Custom Calling Feature Control Codes:[1][2][3]

Service Tone Pulse/rotary
Cancel forwarding[note 1] *30 N/A
Automatic forwarding[note 1] *31 N/A
Notify[note 1] *32 N/A
Intercom ring 1 (short short)[note 2] *51 1151
Intercom ring 2 (short short long)[note 2] *52 1152
Intercom ring 3 (short long short)[note 2] *53 1153
Extension hold[note 2] *54 1154
Malicious caller identification *57 1157
Call blocking *60 1160
Priority call *61 1161
Selective call acceptance *62 1162
Selective call forwarding *63 1163
Caller ID *65 1165
Continuous redial *66 1166
Number display blocking (per call)[note 3] *67 1167
Activate call forwarding on busy *68 1168
Last-call return (incoming) *69 1169
Call waiting disable[note 3] *70 1170
No-answer call transfer *71 1171
Usage sensitive three-way call *71 1171
Call forwarding: start *72 1172
Call forwarding: cancel *73 1173
Speed calling (8 numbers) *74 1174
Speed calling (30 numbers) *75 1175
Anonymous call rejection[note 4] *77 1177
Call blocking disable *80 1180
Priority call disable *81 1181
Caller ID (per call)[note 3][note 5] *82 1182
Selective call forwarding disable *83 1183
Caller ID disable *85 1185
Continuous redial cancel[note 6] *86 1186
Anonymous call rejection disable[note 4] *87 1187
Deactivate call forwarding on busy *88 1188
Last-call return cancel[note 6] *89 1189
Voice-mail *98 1198


See also


 This article incorporates "Federal Standard 1037C".de:Vermittlungstechnische Leistungsmerkmale (öffentliche Netze)

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