to carry, reroute, or remove traffic (see Figure 3-18). This capability enables the net- work to be dynamically reconfigured in outage situations, network restora- tion, traffic variations, or customer needs for time-of-day service. Other benefits include faster installation of circuits, which is important for data services; reduced need to dispatch personnel for circuit provisioning; and ease of reconfiguration, which makes the system more responsive to changes. Again, although proponents of the Ethernet-based architectures advance autodiscovery and self-provisioning, these concepts remain to be fully developed at this time for carrier-class applications. Figure 3-18 points out an important aspect of integrated OAM&P. In asynchronous networks, there are many network elements provided by dif- ferent vendors. The internal overhead channels for each system are not car- ried from one system to another. Typically, pre-SONET FOTS10 A and FOTS B behave as two distinct systems. Thus, separate operator interfaces are needed to perform OAM&P functions, and supportive communications are not carried through the crossconnect. In a SONET network, supportive communications are maintained from one system to the next. This capabil- ity, called single-ended maintenance, enables an entire network to be con- trolled from a single network element. These concepts are also important to vendors developing new Ethernet-based metro systems. Carriers have Figure 3-18 SONET Digital End-to-end OAM&P Cross- SONET NE SONET NE SONET NE SONET NE support. connect OAM&P Communications Only one OAM&P interface required OAM&P communications are integrated between system A and B and crossconnect. Chapter 3 already moved away from disparate systems, particularly at the network management level. They require systems that span the entire end-to-end link, from the original edge device all the way to the termination edge device. SONET also supports enhanced performance monitoring. As noted, SONET overhead is organized into three layers defined as section