
This is a scan of the Operations Support Systems - Operation, Maintenance, and Administration section of the AT&T Practices Master Index, as shown above.
This practice (Master Index) provides an index to all practices developed and maintained by AT&T Technologies, Inc., and identified under the 9-digit numbering plan. These practices are documents authorized by AT&T Technologies, Inc., as the recommended instructions and criteria for planning, engineering, installing, operating, and maintaining telecommunications equipment and software products designed and manufactured by AT&T Technologies, Inc. These practices also play an important part in the training of personnel.
A 9-digit (XXX-YYY-ZZZ) numbering plan is used for AT&T Practices with each practice being assigned an unique 9-digit number in accordance with the subject matter covered. This plan permits organizing information into various categories to simplify and improve indexing. This plan also provides a convenient means for ordering, distributing, and filing practices.
In the 9-digit numbering plan, the first three digits, XXX, identify major categories of information and are referred to as division numbers. The fourth digit, xxx-Y, identifies a subdivision of a given category of information and is referred to as the layer number. The fifth and sixth digits, xxx-yYY, represent a further breakdown and are referred to as sublayer numbers. This scheme permits the breakdown of a division into subcategories of information. The last three digits, xxx-yyy-ZZZ, identify individual practices within a grouping (layers and sublayers) and are referred to as key numbers.