"This standard provides uniform functions and common criteria for performance monitoring (PM) and alarm/status monitoring for digital transmission signals at DS1 and DS3 rates@ those in the SONET hierarchy@ Asymmetrical Digital Subscriber Line (ADSL)@ and Optical Transport Network (OTN). This standard specifies a basic set of monitoring requirements and provides criteria that are common to a set of standards@ the T1.231 series@ which define applications for a specific level in the hierarchy. The documents@ which are included in the T1.231 series (at the time that this document is approved)@ are listed below: T1.231-2003@ Layer 1 In-Service Transmission Performance Monitoring. T1.231.01-2003@ DSL ?C Layer 1 In-Service Digital Transmission Performance Monitoring. T1.231.02-2003@ DS1 ?C Layer 1 In-Service Digital Transmission Performance Monitoring. T1.231.03-2003@ DS3 ?C Layer 1 In-Service Digital Transmission Performance Monitoring. T1.231.04-2003@ SONET ?C Layer 1 In-Service Digital Transmission Performance Monitoring. Purpose The trend towards integrated services networks is a major driving force behind the present emphasis on PM. These networks must support a variety of services such as voice@ digital data@ and video. Each of these services has its own distinct operational characteristics and sensitivity to various network impairments. Very often@ these impairments are not simple@ ""hard"" failures@ but rather ""soft"" (gradual or intermittent) degradations in performance. PM is thus required to capture these effects and provide a basis for effective network maintenance. In turn@ this will enable telecommunications companies to address the increasing concerns of performance-conscious customers. The objective of PM in maintenance is to allow timely detection of performance degradations or related troubles in various network elements@ preferably before the end user is adversely affected. This requires in-service monitoring of performance as opposed to out of service troubleshooting that is normally performed in response to customer trouble reports or failure indications. A variety of approaches to PM currently exist in the industry. Standardized monitoring is important in light of the present multi-vendor environment@ and the need to resolve responsibilities for end-to-end performance degradations at user-tonetwork and network-to-network interfaces. Therefore@ it is desirable to standardize both basic monitoring capabilities and the accessibility of the collected data both locally and remotely. This standard is written to provide the minimal set of requirements to provide for uniform and consistent PM and alarm/status monitoring for the applicable transmission rates. This standard provides definitions for performance primitives (anomalies and defects)@ performance parameters@ and performance failures. Application This standard describes the functions related to the collection@ storage@ thresholding@ and reporting of PM information. It establishes the PM functions that may be used at network interfaces between telecommunication carriers@ at network boundaries@ and at customer premises to permit compatible maintenance operations. Although this standard establishes ranges over which transmission performance can be measured@ it does not establish any requirements or guidelines for levels of performance. This standard refers to other American National Standards that address transmission and performance criteria. In addition@ this standard also uses ITU-T Recommendation G.7710 as a basis for additional details. In those cases@ where this standard (T1.231-2003) and G.7710 disagree@ this standard shall take precedence."