RINGOSTAR – An Evolutionary Performance Upgrade of Optical Ring Networks

INTERNET traffic volumes are growing and require the transmission capacity of the underlying infrastructure to be continuously extended. A closer look at this infrastructure reveals that the Internet architecturally relies on a three level hierarchy consisting of backbone networks, metropolitan area networks, and local access networks. The national or international backbone networks will provide abundant bandwidth by employing wavelength division multiplexing (WDM) links which are interconnected with reconfigurable optical add-drop multiplexers (OADMs) and optical crossconnects (OXCs). The metropolitan area networks (MANs), or metro networks for short, interconnect the backbone networks with the local access networks that carry the data from and to the individual users. By employing advanced local area network (LAN) technologies, such as Gigabit Ethernet (GbE), and broadband access, such as digital subscriber loop (DSL) and cable modems, access networks provide increasing amounts of bandwidth. Most existing metro networks are based on synchronous optical network/synchronous digital hierarchy (SONET/SDH) technology, a circuit-switched networking technology which carries bursty data traffic relatively inefficiently, thus resulting in a bandwidth bottleneck at the metro level. This bandwidth bottleneck, which is widely referred to as the metro gap, prevents the high-speed clients and service providers in local access networks from tapping into the vast amounts of bandwidth available in the backbone. Numerous metro architectures have been proposed and investigated during the past few years, most of them relying on either a ring or, less common, on a star topology. After comprehensively reviewing and comparing the proposed solutions with respect to the requirements specific to the metropolitan area, we argue that a hybrid ring-star network architecture relying on a single-channel packet-switched ring and a single-hop WDM star network is a promising approach for future metro networks to overcome the metro gap. We propose an architecture and corresponding access protocol for such a hybrid network that we call RINGOSTAR. Existing packet-switched ring networks, such as the IEEE 802.17 Resilient Packet Ring (RPR), can be evolutionary, and therefore cost-efficiently, upgraded to the RINGOSTAR network by connecting a subset of the ring nodes to an optical star network using dark fiber which is abundantly available in metropolitan areas. RINGOSTAR builds on two underlying performance enhancing techniques for ring networks which are proposed in this work. The first technique is called proxy stripping and provides a means to significantly increase the capacity of packet-switched ring networks and makes the fixed ring capacity scalable. The second technique, that we call protectoration, enables both fast and bandwidth efficient recovery from multiple link and/or node failures in ring networks that usually can only recover from single failures. Furthermore, we propose mechanisms to enable Quality of Service (QoS) support and fairness control in RINGOSTAR. We comprehensively evaluate the performance of our proposed architecture and the underlying performance enhancing techniques for various network configurations and traffic scenarios, including self-similar and hot-spot traffic, by means of mathematical analysis and verifying computer simulations. Performance results show that, for instance, when interconnecting 32 out of 256 ring nodes via a star subnetwork, proxy striping increases the network capacity for uniform traffic by a factor almost equal to ten.