Traffic forecasting is an important means to facilitate network capacity planning by predicting necessary link upgrades and link additions, but it is generally unable to take into account events that are hard to predict, e.g., breaking news, denial-of-service attacks, and failures. These events, which may be typically short-lived but whose impact on the network traffic load is significant, together with the hard to predict traffic due to the server farm based architecture of the Internet will increase the amount of unpredictable traffic. The so-called network lifetime metric, which measures the ability of a network to sustain unexpected changes and shifts in traffic load, is becoming increasingly important. Very recently reported preliminary results show that the widely deployed bidirectional rings provide the smallest network lifetime, whereas chordal rings perform best in terms of network lifetime. In this paper, we first provide extensive numerical investigations of the network lifetime of bidirectional rings for realistic initial traffic scenarios. We then provide more detailed insights into the network lifetime of chordal rings and show that chordal rings not necessarily outperform bidirectional rings. Finally, we examine meshed rings and a novel hybrid ring-star network which clearly outperform not only bidirectional but also chordal rings in terms of network lifetime for a wide range of unexpected traffic changes and shifts

Both wavelength-division-multiplexing (WDM) networks with a ring architecture and WDM networks with a star architecture have been extensively studied as solutions to the ever increasing amount of traffic in the metropolitan area. Studies typically focus on either the ring or the star and significant advances have been made in the protocol design and performance optimization for the WDM ring and the WDM star, respectively. However, very little is known about the relative performance comparisons of ring and star networks. In this paper, we conduct a comprehensive comparison of a state-of-the-art WDM ring network with a state-of-the-art WDM star network. In particular, we compare time-slotted WDM ring networks (both single-fiber and dual-fiber) with tunable-transmitter and fixed-receiver (TT-FR) nodes and an arrayed-waveguide grating-based single-hop star network with tunable-transmitter and tunable-receiver (TT-TR) nodes. We evaluate mean aggregate throughput, relative packet loss, and mean delay by means of simulation for Bernoulli and self-similar traffic models for unicast traffic with uniform and hot-spot traffic matrices, as well as for multicast traffic. Our results quantify the fundamental performance characteristics of ring networks versus star networks and vice versa, as well as their respective performance limiting bottlenecks and, thus, provide guidance for directing future research efforts.