Abstract

Signal quality monitoring is an important issue for the design, operation, and maintenance of optical transport networks (OTN). From a network operator point of view, monitoring techniques are required to establish connections, establish protection or/and restoration, perform mainte nance, and establish service level agreement. In order to achieve these functions, monitoring techniques should satisfy some general requirements: in-service (non-intrusive) measurement, signal deterioration detection (both SNR degradation and waveform distortion), fault isolation (localize impaired section or node), transparency and scalability (irrespective of signal bit rate and signal formats), and simplicity (small size and low cost). There are several approaches that make it possible to detect various impairments, including both digital and analog techniques: bit error rate (BER) estimation, error block detection, optical power measurement, optical SNR evaluation with spectrum measurement, Q-factor monitoring, and pilot tone detection.^1–9 A fundamental performance monitoring parameter of any digital transmission system is its end-to-end bit error rate (BER). However, the BER can be correctly evaluated only with an outside service BER measurement, by using a known test bit pattern, in place of the real signal. On the other hand, in-service measurement can only give rough estimates through the measurement of digital parameters (e.g., error block detection and error count in forward error correction) or analog parameters (e.g., OSNR and Q-factor).

© 2002 Optical Society of America