Single-Link Failure Detection in All-Optical Networks Using Monitoring Cycles and Paths
In this paper, we consider the problem of fault localization in all-optical networks. We introduce the concept of monitoring cycles (MCs) and monitoring paths (MPs) for unique identification of single-link failures. MCs and MPs are required to pass through one or more monitoring locations. They are constructed such that any single-link failure results in the failure of a unique combination of MCs and MPs that pass through the monitoring location(s). For a network with only one monitoring location, we prove that three-edge connectivity is a necessary and sufficient condition for constructing MCs that uniquely identify any single-link failure in the network. For this case, we formulate the problem of constructing MCs as an integer linear program (ILP).We also develop heuristic approaches for constructing MCs in the presence of one or more monitoring locations. For an arbitrary network (not necessarily three-edge connected), we describe a fault localization technique that uses both MPs and MCs and that employs multiple monitoring locations. We also provide a linear-time algorithm to compute the minimum number of required monitoring locations.Through extensive simulations, we demonstrate the effectiveness of the proposed monitoring technique.
Algorithm / Technique used:
Optical networks have gained tremendous importance due to their ability to support very high data rates using the dense wavelength division multiplexing technology. With such high data rates, a brief service disruption in the operation of the network can result in the loss of a large amount of data. Commonly observed service disruptions are caused by fiber cuts, equipment failure, excessive bit errors, and human error. It is desired that these faults be uniquely identified and corrected at the physical layer before they are even noticed at higher layers. Therefore, it is critical for optical networks to employ fast and effective methods for identifying and locating network failures. Some failures, such as optical cross-connect port blocking and intrusion, can affect a single or a specific subset of wavelengths within a link. Other failures, including fiber cuts and high bit error rates (BERs), may affect all the wavelengths that pass through a fiber duct.
In this work, we focus on the detection of the latter type of failures, and present a fault detection technique that can uniquely localize any single-link failure. For ease of explanation, we use the notion of failure, although the treatment applies as well to assessing other metrics that significantly impact the link performance, such as optical power, optical signal-to-noise ratio (SNR), and BER. In order to rapidly measure the performance of a link (or a collection of links), it is essential to analyze the signal in the optical domain via optical spectrum analyzers (monitors).
Various optical-level mechanisms for failure detection were proposed in the literature. These include optical spectral analysis, optical power detection, pilot tones, and optical time domain reflectometry (OTDR). a failure detection scheme was proposed, in which monitors are assigned to each optical multiplexing and transmission section.
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