n be asked, under manage- ment control, to check for LoL on their incoming fibers. Conversely, where an LSP is being torn down gracefully under the control of a signaling pro- tocol, the LoL condition propagates along the fiber much more quickly than the signaling messages that inform each switch of the situation. In this sit- uation, any downstream OXC that is capable of LoL detection must be pre- vented from raising a false alarm about signal loss. Other management problems in an optical network include communicating information between switches about how optical fiber bundles are addressed at either end of a link and setting up backup links to kick in if a primary link fails. Optical Network Client Interface Currently, optical networks are mostly confined to network cores with existing lower-cost networking tech- nologies bridging the gap between core and edge networks. Therefore, an optical network needs to provide an interface to enable client network devices-such as routers-to dynamically request connections through it over the Optical User-to-Network Interface (O-UNI). All-Optical Networks End Notes 1. For a thorough discussion of these kinds of signaling, see, for example, D. Minoli and G. Dobrowski, Signaling Principles for Frame Relay and Cell Relay Services (Boston: Artech House, 1994). 2. R. A. Barry, "Intelligent Optical Networking, Year 2001: A Practical Perspective," Next-Generation Networks Conference (NGN) 2001 Proceedings. 3. Others, however, state that these proponents prefer the simple diagrams of a few nodes (n) with a few links between them (say, n +m) because these diagrams are much simpler to deal with and to talk around, compared with the reality of the networks that are actually deployed (which indeed look more like the cascaded-ring diagrams that we show throughout this book). Also, because SONET/SDH is historically well suited and optimized for a ring configuration, a way to disentrench SONET is to deprecate the architecture it supports SO well -namely, rings. 4. It is unclear how thes