of performance management and fault management, respectively. Maintenance consists of both preventive and corrective procedures that are designed to (a) prevent troubles and identify potential troubles before they affect service, and (b) detect a network failure that impacts performance and make the appropriate repairs. A typical seven-step maintenance process consists of: Trouble Detection – Detect trouble by continuous monitoring, periodic tests, per-call or other pre-action tests, or other automatic processes. Trouble Notification – Send notification of a specific event or condition to a local display or Operations System (OS). Trouble notifications include output messages and visual and audible alarms. Service Recovery – Minimize the degradation of service by automatic or manual protection actions. Trouble Verification – Determine whether the reported condition still exists. Trouble Isolation – Isolate the trouble to its source, preferably to a single field-repairable element, e.g., circuit pack. Repair – Fix or replace the faulty element. Repair Verification and Return to Service – Verify that the trouble has been fixed and return the element to service. Telcordia GR-474 establishes trouble-detecting and reporting criteria for signal transmission failures and internal hardware or software anomalies. GR-474 provides proposed generic requirements that pertain to the Fault and Performance Management functions in transport and switching NEs used for alarm surveillance and control. GR-474 complements recent criteria in industry standards such as ITU-T Recommendation M.3100, G.707, and G.709, and ANSI T1. State models A network element state model facilitates cross domain network management and promotes a multi-vendor environment. The standard definitions and mappings allow Operations Systems to gather state information from NEs and integrate it into a consistent representation of the status of the entire managed network and each of the services that it supports. Telcordia GR-1093 discusses the two primary state models in industry. One is the Telcordia State Model, which consolidates the state models previously described in several Telcordia documents. By consolidating the models, changes and expansions to the models can be presented and can evolve in a coordinated fashion. Also, inconsistencies and redundancy may be averted. The other model is the International Organization for Standardization (ISO) State Model, which is defined in ITU-T Recommendation X.731. The state of an entity represents the current condition of availability of the underlying resource or service in the NE from the point of view of management. In the context of the Telcordia State Model, the term "entity" represents an entry in a TL1