Optical Network Control: Architecture, Protocols, and Standards

3.6. When Things Go Wrong

One of the most important aspects built into optical transport systems is their “self-diagnosis” capability. That is, the ability to detect a problem (i.e., observe a symptom), localize the problem (i.e., find where it originated), and discover the root cause of the problem. In fact, SONET and SDH include many mechanisms to almost immediately classify the root cause of problem. This is done by monitoring the signal integrity between peers at a given layer, and also when transferring a signal from a client (higher) layer into a server (lower) layer (Figure 2-17).

In the following, we first consider the various causes of transport problems. Next, we examine how problems are localized and how signal quality is monitored. ...