Djamel Amar

Spectrum fragmentation issue in flexible optical networks: analysis and good practices

Flexible grid optical networks allow an efficient utilization of spectrum resources using 12.5-GHz frequency slot multiples instead of a fixed spacing, introducing however spectrum fragmentation (SF). In the literature, SF is often assumed to be a serious problem specifically in a dynamic traffic context. It is mostly related to the bandwidth blocking ratio due to the lack of relevant comparison criteria and efficient metrics. Besides, in operator core network, traffic behavior is instead incremental and it is forecasted for short periods of time in addition to some operational constraints that make of it a specific context. In this work, we present an exhaustive analysis and an accurate evaluation for SF issue in flexible optical networks. We also propose new metric for fragmentation measurements and some approaches to address such a problem.

Multilayer restoration in elastic optical networks

Optical restoration is known to be an effective way to save on network overall cost, using the same available equipment previously used before the failure occurs. However, when backup paths are too long, some regenerators can be required bringing into question the expected gain. In this work, we show that transponder datarate elasticity is a successful approach to address this issue, taking benefit of best effort traffic low priority in a multilayer context.

Optical power control in GMPLS control plane

The exponential traffic growth in optical networks has triggered the evolution from fixed-grid to flex-grid technology. This evolution allows better spectral efficiency and spectrum usage over current optical networks in order to facilitate huge dynamic traffic demands. The promise of flex-grid technology in terms of increasing the number of optical channels established over optical links, however, may not be sustainable because of the associated increase in optical amplification power. In this work, we detail a power control process that takes advantage of link optical power and channel optical signal-to-noise ratio (OSNR) margins to allow network operators to support this optical power increase while maintaining the use of legacy optical amplifiers. New generalized multiprotocol label switching (GMPLS) protocol extensions are proposed on which to integrate the optical power control process in the control plane. The performance of the process is evaluated in terms of the blocking ratio and network throughput over fixed-grid and flex-grid networks. Results show that controlling optical power benefits from the flex-grid technology in terms of spectrum and capacity gain and reduces optical connection blocking.

Class-of-service-based multilayer architecture for traffic restoration in elastic optical networks

In this work, we propose and investigate a class-of-service-based multilayer architecture for traffic restoration in elastic optical networks. This architecture benefits from both data rate elasticity and low quality of service requirements of best-effort traffic in IP-over-WDM optical networks, combining 1 + 1 IP protection for gold traffic and optical restoration for best-effort traffic. Numerical simulations reveal that the proposed architecture can further reduce capital expenditures, even with the significant extra cost of elastic transponders.

On the legacy amplifier limitation in flexgrid optical networks

Flexgrid technology is an interesting solution to improve network capacity. However, for a given spectral band, it gives rise to the increase of the number of channels, requiring more amplification power in respect with the conventional fixed grid technology. In this work, we demonstrate that re-engineering the link margins allows supporting this increase while keeping in use legacy amplifiers.

Traffic forecast impact on spectrum fragmentation in gridless optical networks

Gridless Technology increases the spectral efficiency of optical fiber transmissions, introducing however spectrum fragmentation. In this work, we show that traffic forecast permits to avoid spectrum fragmentation, even with an uncertainty of 10% on the growth rate.

WDM slot sharing of colored optical packets for latency improvement and Class of Service differentiation

The optical packet switching technology has been identified as a key technology to offer data rate and modulation format transparency, fine switching granularity and efficient bandwidth utilization. The ANR N-GREEN project proposes a novel over-dimensioned switch/router node with colored optical packet concept. In this work, we propose a new WDM slot sharing approach that significantly improves N-GREEN node-level latency, and show that it is quite effective for Class of Service differentiation in the optical domain.

Link Design and Legacy Amplifier Limitation in Flex-Grid Optical Networks

Flex-grid technology is an effective means to improve the spectral efficiency of optical communication. For a given amplifier spectral bandwidth, it gives rise to the increase in the number of optical channels as it reduces channel spacing. Therefore, in order to reap full benefits from the flex-grid saved spectrum, further amplification power is required with respect to conventional fixed grid. This is a strong limitation if the legacy amplifiers cannot meet this new requirement due to their optical power limits. In this paper, we demonstrate that exploiting the link margins allows the support of this increase while maintaining in use legacy amplifiers.

Optical power control to efficiently handle flex-grid spectrum gain over existing fixed-grid network infrastructures

The exponential traffic growth in optical networks has triggered the evolution from Fixed-Grid to Flex-Grid technology. This evolution allows better spectral efficiency and spectrum usage over current networks in order to facilitate dynamic and huge traffic demands. The integration of Flex-Grid technology increases the number of optical channels established over optical links, leading, however, to an increase in amplification power and possibly saturating optical amplifiers. In this work, we propose a power adaptation process that takes advantage of link optical signal to noise ratio (OSNR) margins to allow network operators to support this power increase while maintaining the use of legacy amplifiers. Results show that controlling channel optical power benefits from the Flex-Grid in terms of spectrum and capacity gain using in-place amplifier infrastructure.