T. Zami

The relevant impact of the physical parameters uncertainties when dimensioning an optical core transparent network

We illustrate the importance to consider physical uncertainties in the quality of transmission estimators used for impairment constrained based routing. Power uncertainties of 1 dB yield 80% of further regenerators.

Interest of an adaptive margin for the Quality of Transmission estimation for lightpath establishment

We justify a lightpath characteristic dependent margin when estimating the quality of transmission for the establishment of a connection by showing the resulting better prediction accuracy and eventually the reduction of the required transmission resources.

Driving technologies addressing the future dynamic transparent core networks

Reconfigurable transparent networks are now a reality in the core layer thanks to the implementation of innovative transmission and wavelength routing sub-systems. Transparency on a large scale opens up new perspectives in terms of scalability and flexibility. There are numerous promising technologies to achieve that goal but it is likely that only few of them will really prevail in the field. For instance, the compliance with the already installed transmission infrastructures or the power consumption consideration may prevent a technology from appearing in a real optical network. This paper presents some of our current research directions that exhibit a high potential to meet the market requirements for the future dynamic transparent core networks.

Higher capacity with smaller global energy consumption in core optical networks due to elastic channel spacing

We propose a novel model for core optical networks combining benefits of transparent and opaque networks through variable channel spacing. We demonstrate increased capacity at limited energy cost through detailed transmission experiments and network planning.

Importance of reliability when dimensioning an optical transparent network with physical impairments awareness

Optical network telecommunication operators are adopting optical transparency to make the channel routing more flexible, optimize their cost and meet customer requirements. But, the optical signal accumulates physical impairments along the transmission so that its quality should be assessed before setting-up the connection. The relevance of an estimate depends on the uncertain knowledge of the physical parameters. This paper shows the importance of accounting for uncertainties within a physical impairment aware dimensioning tool.

Optimized synergy between 10 Gb/s and 40 Gb/s channels on a partially transparent network

As optical networks are moving towards transparency to save expensive optoelectronic conversions, 40 Gb/s transmission technology appears on the field to meet the increasing capacity requirements. An advantage of transparent network is its independence of the bit rate and modulation format. Hence the transition from 10 to 40 Gb/s in a transparent network can be imagined as a gradual replacement of transponders working at 10 Gb/s with transponders at 40 Gb/s and the co-existence of both bit rates. In this paper we propose a routing method optimizing the exploitation of unused capacity in 40 Gb/s channels and also reducing the number of optoelectronic devices; we name this criterion ‘10/40 Gb/s synergy’. We show that routing 10 Gb/s demands at different bit rates is more performing than a routing at a fixed bit rate; we also show that the synergy minimize the number of required 40 Gb/s transponder as a function of traffic characteristics.

‘10Gb/s-40Gb/s Synergy’ routing to better exploit network capacity

We introduce a new routing method, 10-40 Gb/s synergy, that reduces the blocking probability of at least 15% against classical routing with both bit-rates. The transmission estimator enables better performance.

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.

Robustness of Quality of Transmission estimators for IC-RWA to uneven channel powers in core optical networks

The quality of transmission (QoT) estimators, envisaged to optimize the impairment constraint routing and wavelength assignment (IC-RWA) in optical transparent networks, are often assessed in a steady configuration by means of re-circulation loops and/or transmissions simulations. In such context the powers of the WDM channels are regularly fixed to a given set of values related to a given point of the periodical transmission. But in installed systems these powers may become uneven, for instance because of the imperfect flatness of optical amplifiers gains over the band occupied by the transmitted WDM comb. In such a frame of a most realistic channel power evolution, this paper investigates the predictions accuracy of a QoT estimator in terms of non-linear effects impact. Hence, we achieved transmission simulations of 50 GHz-spaced channels over several network sections featuring optical amplifiers with no perfectly flat gain. Despite such feature, it appears that the non-linear phase remains a well suited parameter to characterize the penalties induced by the non-linear effects provided that the channel powers excursion remains in the range [-1 dB, 1 dB].