This standard applies to Layer 1, dedicated digital services, which are characterized by established transmission paths (i.e., no access or disengagement functions). Therefore, this standard defines performance parameters relevant to the information transfer phase only. This standard provides a list of the performance parameters and measurement methods needed by users, vendors, and providers of dedicated digital communications services, to characterize the user-observable performance of these services (i.e., it does not address the causes of errors). It also provides a formula for arriving at the thresholds of performance that will indicate the transitions between the available and unavailable states. A given service will only reference those parameters or thresholds that are applicable to that service. The network-specific parameters are for performance allocation and network control. End users may use the concepts in this standard to measure end-user-to-end-user performance and availability. Formerly known as T1.503-2002(R2006).