Custom Local Area Signaling Services

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Custom Local Area Signaling Services (CLASS) are PSTN telephony intelligent network services beyond basic voice calling, such as caller ID (automatic number identification (ANI)), caller number blocking, automated call return, call blocking or screening. Different IXCs offer various services.

The services rely on the ITU-T standard Signalling System 7 (SS7) connectivity between network switches (SSPs) and databases (800 Database, LNPDB, LIDB, etc.) to operate. The CLASS standards were defined by Bellcore in the 1970s.

Other services such as call forwarding, three-way calling, call waiting, or speed dialing are part of custom calling rather than CLASS.