issuance of bell system practices within the bell system started around 1930, when they replaced a similar compendium, the "at&t specifications". initially bsps were identified by mixed alphanumeric sequence numbers designating a section and a specific document number within each section. the sections consisted of one letter and two digits, followed by a period character and a three-digit document number. the version of each document was indicated by an issue number. for example, the section designation "c34.175 issue 1" identified a document entitled "station dials—2 and 4 types—maintenance".