Trends in Layered Network Management of ATM, SONET, and WDM Technologies For Network Survivability and Fault Management

Because of the advent of a newero transmission technologies, such as ATM switches and Wavelength Division Multiplexing (WDM), and the intermixing with a oldero technologies, such as SONET Add-Drop Multiplexers (ADMs) and Digital Cross-Connect Systems (DCSs), an important aspect of current work in fault management in the analysis of and response to network failures in multilayered networks. For the last ® ve years, the survivability performance group of T1 (T1A1.2) in the U.S. has had the responsibility of characterizing network outages and the survivability methods used to counteract them. One of the principal techniques that T1 established is the modeling of different network layers. T1’ s inaugural technical report, A Technical Report on Network Survivability Performance, (T1 Technical Report Number 24, November 1993), characterizes the public networks of today as consisting of multiple layers, mainly distinguished by the general technology of equipment that does the switching or cross-connect function within that layer. Four layers (from top to bottom) are de® ned: service, logical, system, and physical, wherein the physical layer is further subdivided into the media and geographi cal sub-layers. Within this framework, each layer is composed of one or more networks (or subnetworks), with each network composed of connections (an active exchange of information between two network points), nodes (equipment that switch or route connections), and links (logical or physical transport of signals between node-pairs). The networks in different layers are coupled, in that the units of link-capacity of a network at one layer, sometimes referred to as a a cliento network, are transported by connections in a lower layer (a servero ) network. In terms of the