The explosive growth in data centric traffic and demand for diverse services are driving the migration of optical communication systems toward packet switched networks. Optical packet switched (OPS) networks offer the unique combination of encompassing the enormous capacity of the optical domain while providing versatile connectivity afforded by individual packet routing.
The key performance metrics of OPS networks at the logical layer, including throughput, latency, scalability, and packet-loss-rates have been studied extensively for various architectures. However, the physical layer performance, a critical measure of the feasibility of packet switched networks intended for implementation in the optical domain, is not well understood in this context. In OPS networks optical packets are typically self-routed through a complex web of interconnection topologies. The exact path any packet may take is not often known, as the routing mechanism may be performed statistically to achieve fairness and load balancing. Furthermore, the data structure carried within the packet may be diverse and include data encoded in different bitrates and modulation formats.
Thus, whereas it may be shown that the logical topology scales in terms of the network layer performance metrics, it does not necessarily follow that the physical layer with complex optical packet propagation also scales in terms of maintaining end-to-end signal integrity.
In this proposed exploratory research the PI will aim to achieve a methodology for evaluating the integrated physical/logical layers performance in OPS networks that truly encompasses the diverse set of scaling metrics and captures the complex nature of optical signal propagation in these networks. To accomplish these goals an experimental investigation will be performed employing a unique, integrated system of a fully connected 12-port OPS network containing 36 switching elements. This experimental test-bed will enable direct coupling between numerical and analytical modeling with realistic data propagated end-to-end through a complete implemented OPS network.
Intellectual Merit: The proposed exploratory research will establish a novel methodology for bridging the gap between the network logical and physical layers in OPS communication systems. These activities will create the groundwork for an emerging field of research that integrates two currently separate disciplines. The merging of the logical and physical layers will enable an integrated systems approach to a new understanding of the critical performance metrics for OPS networks. Unlike electronic systems, the physical layer of optical communication systems is subject to numerous impairments arising from the interactions (linear and nonlinear) of the optical field with the transport medium, switching elements, and amplifiers. Thus, the total complex system performance cannot be decoupled into its physical and logical component layers and must be studied in an integrated fashion. The tools to perform this investigation however do not yet exist. In this proposed exploratory research program the PI will perform realistic traffic routing experiments in a completely implemented optical packet switched network element. These experiments will stress the physical layer scalability as incoming packets to each of the ultra-high capacity ports may contain payload data that spans the WDM C-band. The entire payload is transparently routed end-to-end through the network element and thus may include a diverse set of modulation speeds and formats encoded along the multiple payload wavelengths. These experimental investigations by directly coupling the physical and logical layers, will enable the creation of a truly integrative systems model for the performance of OPS networks.
Broader Impact: Clearly, the migration of optical communication systems is headed toward dynamic networks driven by the explosive growth of packetized data centric traffic. OPS networks offer the potential of exploiting the enormous capacity of lightwave communications while delivering fine grained connectivity to a multitude of traffic destinations via individual packet routing. The diverse set of data structures, encoding, and modulation schemes enabled by the transparent end-to-end payload path creates a network element that can potentially seamlessly evolve with many new network generations. Test-bed experiments and modeling employed to demonstrate the integrated physical/logical layers performance scalability will enable intelligent design of future ultra-high capacity packet switched systems.
