Configurable processors enable dramatic gains in energy efficiency, relative to traditional fixed instruction-set processors. This energy advantage comes from three improvements. First, configuration of the instruction set permits a much closer fit of the processor to the target applications, reducing the number of execution cycles required. Second, configuring the processor removes unneeded features, reducing power and area overhead. Third, automatic processor generation tools enable logic optimization, signal switching reductions, and seamless mapping into low-voltage circuits and processes, for very low-power operation. The first improvement has been well-studied. Analysis of the second and third improvements requires detailed circuit and layout experiments, which is the primary focus of this paper.Starting from a range of existing available power saving options, this work explores the tradeoff and analyzes the results: the design priority tradeoff, the process technology impact, and implementing low-power configurable processor using commercial scaled-VDD cell libraries compatible with mainstream SOC practices. These real processor designs can achieve power dissipation approaching 20μW/MHz at 0.8V and close to 10μW/MHz at 0.6V, using production 0.13um libraries. Finally, this work quantifies the dramatic process, voltage and temperature dependence in post-layout leakage power for small processor designs.

As WDM technology matures and multicast applications become increasingly popular, supporting multicast at the WDM layer becomes an important and yet challenging topic. In this paper, we study constrained multicast routing in WDM networks with sparse light splitting, i.e., where some switches are incapable of splitting light (or copying data in the optical domain). Specifically, we propose four WDM multicast routing algorithms, namely, Re-route-to Source, Re-route-to-Any, Member-First, and Member-Only. Given the network topology, multicast membership information, and light splitting capability of the switches, these algorithms construct a source-based multicast light-forest (consisting one or more multicast trees) for each multicast session. The performance of these algorithms are compared in terms of the average number of wavelengths used per forest (or multicast session), average number of branches involved (bandwidth) per forest as well as average number of hops encountered (delay) from a multicast source to a multicast member.

As WDM technology matures, IP over WDM multicast will become a challenging new topic. Supporting multicast at the WDM layer provides additional advantages, but also raises many new issues that do not exist in IP multicast. For example, the limitation on the light splitting capability of switches is one major difficulty in WDM multicast, and in addition, the limitations on both the wavelength conversion capability and optical buffer space may affect multicast routing as well. In this paper, we focus on the IP over WDM multicast routing problem, i.e. how to construct multicast trees at the WDM layer based on IP multicast routing protocols. More specifically, we study how label switched paths for optical label switching can be set up for multicast traffic. We propose two approaches, one without modification of existing IP multicast routing protocols, and the other with modification of existing IP multicast routing protocols.

Supporting WDM multicasting in an IP over WDM network poses interesting problems because some WDM switches may be incapable of switching an incoming signal to more than one output interface. An approach to WDM multicasting based on wavelength-routing, which constructs a multicast forest for each multicast session so that multicast-incapable WDM switches do not need to multicast, was proposed and evaluated previously. Such an approach requires global knowledge of the WDM layer. In this paper, we study WDM multicasting in an IP over WDM network under the framework of multiprotocol label switching (MPLS) using optical burst/label switching (OBS/OLS). We propose a protocol which modifies a multicast tree constructed by distance vector multicast routing protocol (DVMRP) into a multicast forest based on the local information only.