Architecture and Access Protocol for a Wavelength-Selective Single-Hop Packet Switched Metropolitan Area Network

Abstract

Current SONET/SDH metro ring networks create the so–called metro gap which prevents high– speed clients from tapping into the vast amounts of bandwidth available in the backbone. To bridge this gap we propose and investigate by means of analysis and simulation a novel arrayed– waveguide grating (AWG) based single–hop wavelength division multiplexing (WDM) network with a physical star topology. Star networks offer a better optical power budget than ring and bus networks and are easy to install, configure, manage, and troubleshoot. Unlike their multihop counterparts single–hop networks provide a minimum mean hop distance (unity), inherent transparency, future–proofness, easy upgradability, simplified management, and an improved throughput–delay performance since no bandwidth is wasted due to packet forwarding. Owing to spatial wavelength reuse the AWG keeps the wavelength pool small which enables the deployment of fast tunable transceivers with a negligible tuning time. The proposed network consists of an AWG with wavelength–insensitive combiners (splitters) attached to each AWG input (output) port, where the splitters are used for realizing optical multicasting. Due to its completely passive nature the network is cost–effective and reliable. Each node at the network periphery is equipped with one single tunable transceiver and one low–cost broadband light source which is spectrally sliced for broadcasting control information. Direct sequence spread spectrum techniques are deployed to improve the network security and enable simultaneous transmission of data and control within the same wavelength channel without requiring any additional control wavelength and receiver. Each node has access to all wavelengths resulting in efficient multicasting and load balancing. Wavelengths are on–demand allocated by means of a reservation medium access control (MAC) protocol which provides both packet and circuit switching. By not fixed assigning the reservation slots and deploying performance enhancing reservation ALOHA (R–ALOHA) and code division multiple access (CDMA) the network is made scalable. All nodes have global knowledge and schedule variable–size packets on a deterministic first–come–first–served and first–fit basis without requiring explicit acknowledgements guaranteeing fairness, decreased latency, and quality of service (QoS) and completely avoiding both channel and receiver collisions of data packets. The network efficiency is significantly increased by spatially reusing all wavelengths at each AWG port, exploiting multiple free spectral ranges (FSRs) of the AWG, and wormhole scheduling. For unicast packet switched traffic our AWG based network achieves a mean wavelength utilization of more than 100%, a mean channel utilization of approximately 53%, and a mean aggregate throughput that is about 70% larger than the maximum aggregate throughput of the DT–WDMA access protocol that runs on a PSC based single–hop metro WDM network. Partitioning in conjunction with spatial wavelength reuse and exploiting the reservation phases of the MAC protocol allow for very efficient multicasting. Furthermore, the presented single–hop network significantly reduces the complexity of the protocol stack in that routing is replaced with simple wavelength tuning and the data link layer can be omitted. By using computationally efficient multiobjective optimization tech-