Physical-layer attacks in all-optical WDM networks

The high data rates employed by transparent optical networks (TONs) based on Wavelength Division Multiplexing (WDM) make them most suitable for satisfying today´s intensive growth of network traffic. The absence of optoelectronic conversion at intermediate nodes forming all-optical connections, called lightpaths, provides total data transparency to data formats and protocols in such networks. However, it also allows for malicious signals to propagate through parts of the network without being discarded at such intermediate nodes. Certain vulnerabilities of the main physical components in TONs, i.e., optical fibers, amplifiers and switches, can be exploited to perform malicious attacks on the physical layer. Most failure and attack management approaches are reactive and focus on network recovery after a fault or an attack has already occurred. Recently, novel, prevention-oriented safety strategies have been proposed to aid attack localization and source identification in network planning phase. This paper provides an overview of optical network component vulnerabilities which can be exploited to perform attacks and known attack methods which can disrupt the proper functioning of the optical network. Furthermore, it gives an overview of network planning approaches which deal with physical-layer security issues in TONs and emphasizes the need for new, preventive strategies for decreasing the vulnerability of transparent optical networks.