Testbed methods to study physical layer path establishment in long haul optical wavelength switched networks

To cope with increasing traffic, optical networks have steadily adopted faster interfaces. Interfaces working at 40 Gb/s were recently introduced in networks already deployed at 10 Gb/s; moreover, 100 Gb/s interfaces have been demonstrated in laboratory experiments [1]. As this upgrade in bit-rate tends to evolve over time scales faster than the lifetime of deployed systems, wavelength division multiplexed (WDM) systems may be required to support simultaneous transmission of signals modulated at different rates. These signals can have very different transmission properties and optimal designs often employ unique modulation formats for each bit rate. For example, non return to zero on-off keyed modulation is commonly used at 10 Gb/s, whereas phase-shift-keyed modulation formats, such as differential phase shift keying, are used at 40 Gb/s. More complex modulation formats are proposed at 100 Gb/s and recent studies consider the use of orthogonal frequency division multiplexing to make the channel capacity flexible, ranging from 10 up to 100 Gb/s and higher [2]. This wide variation in modulation technologies motivates the use of a network infrastructure that supports transmission heterogeneity without costly changes when a new bit rate or format is introduced. Transparent networks have the advantage of providing a flexible infrastructure with the potential to enable the introduction of new modulation technologies by changing only the extremity interfaces. Optical transparency is possible thanks to the introduction of optical switches, such as wavelength selective switches (WSS), avoiding systematic optoelectronic conversion at nodes, and also thanks to improvements in transmission performance, enabling reaches of several thousand kilometers and many nodes before needing optoelectronic regeneration.