In addition to learning about the switch type your service provider uses, you also need to know what Service Profile Identifiers (SPIDs) are assigned to your connection.

The ISDN carrier provides a SPID to identify the line configuration of the ISDN service.

SPIDs are a series of characters (that can look like phone numbers) that identify your network to the switch at the CO.

After you're equipment is identified, the switch links the services you ordered to the connection.

Work on standards for ISDN began in the late 1960s.

A comprehensive set of ISDN recommendations was published in 1984 and is continuously updated by the Consultative Committee for International Telegraph and Telephone (CCITT), now the International Telecommunication Union Telecommunication Standardization Sector (ITU-T).