Alexandros Stavdas

An OXC Architecture Suitable for High Density WDM Wavelength Routed Networks

A novel optical crossconnect architecture, capable for tens of terabit throughput and allowing the integration of wavelength and space switching, is presented for both WP and VWP networks. The architecture offers significant advantages in terms of crosstalk performance and node complexity. In the architecture, there are no crossovers and crosspoints. Therefore, the signal-to-crosstalk ratio per wavelength channel can be very high since each channel is processed independently from the others. This will also allow to introduce other all-optical techniques like adding/dropping of OTDM channels as well as optical regeneration. The proposed architecture is wavelength and link modular and particularly suitable for crossconnects with a very large number of wavelength channels. Performance aspects of a single as well as of a cascade of crossconnects have been simulated using a simulation tool.

A MAC protocol for efficient multiplexing QoS-sensitive and best-effort traffic in dynamically configurable WDM rings

Slotted dynamically re-configurable Metropolitan rings are viewed as a viable alternative to WDM channel overprovisioning since they allow statistical sharing between the channels. A challenge these networks are facing is to simultaneously transport both delay sensitive and best-effort traffic. In this work, a strategy for mixing up different QoS classes efficiently in a dynamically re-configurable ring is proposed. The scheme is based on explicit class reservations for the delay-sensitive first priority traffic, which are allowed to fluctuate in accordance with demand. In contrast, best effort traffic is using only any bandwidth left over by the high QoS traffic, thus exploiting the elastic behaviour of best-effort traffic and its closed loop control. The performance of the proposed mechanism is evaluated via simulations demonstrating access delay below the round trip time for high priority traffic and good overall system efficiency by filling any spare capacity with best-effort traffic, which was buffered during busy periods.

A WDM control architecture and destination conflicts analysis

The well-known Single-hop Wavelength division multiplexing (WDM) networks using passive star topology, provide direct connection between the source and the destination of a data packet but require some pretransmission coordination between the stations over a control channel. Since the electronic processing bottleneck that the single control channel architecture introduces is high, we propose a new WDM control architecture to overcome this problem. Also, we develop and analyse a queueing model of the network in order to obtain the queue length distribution and loss probabilities at the receiving sides of the stations. A rigourous method is developed to examine the receiver collision phenomenon and to evaluate the performance reduction due to the finite number of tuneable receivers at each station and finite population. Copyright

Implementation of medium access control for interconnecting slotted rings to form a WDM metropolitan area network

Feature Issue on Optical Interconnection Networks (OIN). A system of slotted interconnected rings employing a combination of wavelength-division multiple access (WDMA) with time-division multiple access (TDMA) can serve a metropolitan area without electro-optical conversion and buffering of payload except at system entry points. The multiple rings overcome the power budget limitations of the single ring extending the reach of the system to even the largest metropolitan areas, the WDM dimension provides flexibility and ease of evolution, and the TDMA dimension offers the efficiency of multiplexing gain particularly under bursty traffic. The system control information is transferred on a dedicated wavelength and is processed in the electrical domain at the ring nodes and the hub, which interconnects the rings. The algorithms control the access to each ring and the scheduling of slots among the rings, based on explicit reservations, to adapt efficiently to the fluctuating offered load. We present the design and hardware implementation of the access control algorithms for such a system built in the framework of the Information Society Technologies (IST) project DAVID (data and voice over DWDM).

On Multi-λ Packet Labeling for Metropolitan and Wide-Area Optical Networks

Bit-asynchronous optical packet-switched networks are seen as viable candidates for Metropolitan areas. For such networks we are proposing labeling of the optical packets based on multidimensional headers constructed by using a combination of two or more physical properties like time, wavelength, sub-carried frequency, or polarization state. The resulting header can be processed using slower electronics than the line rate without any sacrifice of the information transfer rate and with higher immunity with respect to degradation of the optical signal-to-noise ratio (OSNR). Packet identification as well as header-payload separation is achieved using passive devices. This method for constructing and switching information as well as transporting frames offers potential speed processing gains over the binary case as well as improvements on bit-error rate versus OSNR. The feasibility of using headers constructed by combination of wavelength and in terms of dispersion and spectral efficiency is established as a function of bit-rate and distance. Finally a generic architecture for a suitable optical packet add/drop node is described.

Probability density function of four wave mixing crosstalk in WDM systems

The probability density function of four-wave-mixing crosstalk in wavelength-division-multiplexing systems is derived analytically in a closed-form formula. For dispersion shifted fiber the plots were given for different number of channels, different channel indexes and different channel spacings. The comparison with Gaussian approximation is given, and the limits of its application are pointed out.