ave inventory information on facil- ities available for provisioning and may be used to support provisioning by sending remote-control commands to enable or disable circuits. Many car- riers have an extensive Operations Systems Network (OSN) that trans- ports both the OSS-OSS, OSS-NE, and NE-NE traffic. Chapter 3 Standardization efforts were undertaken in the 1990s to formulate a common operation systems network architecture. The Telecommunications Management Network (TMN) Standards Committee agreed on an OAM&P architecture and formulated implementation standards for it. 9 SONET sup- ports the TMN's architecture for OAM&P data communications. The basic architecture for OAM&P communications as defined by the ITU is shown in Figure 3-17. TMN is a framework for an OSS to communicate with the net- work (more accurately, its network elements), and vice versa. An OSS com- municates with the network elements either directly or through mediation devices. SONET has improved network management compared with the tech- nology before it by providing extra bandwidth and functionality in the over- head structure to facilitate the NE-NE and NE-OSS information flow. The overhead bytes support OAM&P data channels (called data communi- cations channels [DCCs]), enabling communications between intelligent controllers and individual network elements, as well as internode commu- Figure 3-17 Operations Basic TMN Systems architecture. Communications Network Mediation Device Communications Network Network Network Element Element Traditional SONET Architectures nications. This communication, although in band in the physical channel, is logically out of band; in fact, it is in a separate TDM-like channel. In con- trast to this, the emerging Ethernet-based technologies either have no, or very limited, OAM&P data flows (for example, metro systems based on GbE) or are developing in-band messages commingled with the data flow, which carry only a subset of the SONET OAM&P functionality. SONET enables circuits to be remotely enabled or disabled 