Multi-state power management of communication links

The continuing speed increases of communication links at all levels from intra-server interconnects all the way to WAN results an increasing amount of network power consumption. Thus an effective, multi-level and multi-scale power management of communication links is increasingly important. In this paper we propose algorithms that can reduce link power consumption by exploiting three key attributes: (a) available non-operational low power (or sleep) states, (b) link width modulation, and (c) link speed modulation. Although shutting down inactive links at coarse time scales is well known, our emphasis is primarily on finer-time granularities and can be used in addition to coarse grain methods. The paper explores considerations in designing such algorithms and provides some specific algorithms and their parameterization. We show that the link width modulation is the most attractive alternative when available, but other controls are also useful. The techniques explored can be applied to a wide variety of links in modern systems.