Introduction This section details the purpose and scope of the reliability prediction procedure and indicates changes from the previous issue （SR-332， Issue 1， May 2001）。 1.1 Purpose and Scope A prediction of reliability is an important element in the process of selecting equipment for use by telecommunications service providers and other buyers of electronic equipment. As used here， reliability is a measure of the frequency of equipment failures as a function of time. Reliability has a major impact on maintenance and repair costs and on the continuity of service. The purpose of this Reliability Prediction Procedure （RPP） is to document recommended methods for predicting device and unit hardware reliability. This procedure also documents a recommended method for predicting serial system hardware reliability. It contains instructions for suppliers to follow when providing predictions of their device， unit， or serial system reliability （hereinafter called “product” reliability）。 It also can be used directly by telecommunications service providers for product reliability evaluation. Device and unit failure rate predictions generated using this procedure are applicable for commercial electronic products whose physical design， manufacture， installation， and reliability assurance practices meet the appropriate Telcordia （or equivalent） generic and product-specific requirements. This procedure cannot be used directly to predict the reliability of a non-serial system. However， the unit reliability predictions resulting from application of this procedure can be input into system reliability models for prediction of system-level hardware reliability parameters. Troubles caused by transient faults， software problems， procedural errors， or unexpected operating environments can have a significant impact on system-level reliability. Therefore， system hardware failures represent only a portion of the total system trouble rate. Currently， this procedure also includes some discussion of system-level operating and configuration information that may affect overall system reliability. The procedure directs the requesting organization to compile this information in cases where the unit-level reliability predictions are computed for input to a specific system reliability model. This system-level information is not directly necessary for computation of the unit-level reliability predictions， but these information requirements are not currently addressed in any other Telcordia requirements document and， therefore， are included in this Special Report （SR）.