hich are required of record-keepers, specify the absolute minimum acceptable requirements and generally apply to safety, protection, performance and compatibility. Optional advisory criteria, which are considered to be above the minimum requirements, are viewed as desirable enhancements to the standard. Identifiers, as specified by the standard, are included as part of the record assigned to each element of the telecommunica- tions infrastructure and must be unique. Enclosed identifiers may include additional information-cable, termination position, work area or closet location. Labels, including these identifiers, must meet the legibility, defacement, adhesion and exposure requirements of Underwrit- ers Laboratory 969 and should be affixed in accordance with the UL-969 standard. Bar codes, when included on labels, must use either Code 39, conforming to USS-39, or Code 128, conform- ing to USS-128. Labels must also be color-coded to distinguish demarcation points and campus, horizontal, and riser or back- bone termination points. Pathways must be labeled at all endpoints located in tele- communication closets, equipment rooms or entrance facilities. All horizontal and riser/backbone cables must be labeled at each end. All splice closures must be marked or labeled. Termination hardware, including termination positions, must also be labeled, except where high termination densities make such labeling im- practical. The telecommunications main grounding busbar, as well as each bonding conductor and telecommunications grounding busbar, must be marked or labeled. Finally, each telecommuni- cations space, whether telecommunications closet, equipment room or work area, must be labeled. Each record defined in the standard must contain certain re- quirement information and required linkages to other specified records. Linkages define the logical connections between identi- fiers and records. Identifiers then may point to more than one record. Descriptions of optional information and linkages to 266 - The Telecom Handbook C