MEASURING AND REDUCING ENERGY-CONSUMPTION OF NETWORK INTERFACES IN HAND-HELD DEVICES

Next generation hand-held devices must provide seamless connectivity w hile obeying stringent power and size constrains. In this paper we exa mine this issue from the point of view of the Network Interface (NI). We measure the power usage of two PDAs, the Apple Newton Messagepad an d Sony Magic Link, and four NIs, the Metricom Ricochet Wireless Modem, the AT&T Wavelan operating at 915 MHz and 2.4 GHz, and the IBM Infrar ed Wireless LAN Adapter. These measurements clearly indicate that the power drained by the network interface constitutes a large fraction of the total power used by the PDA. We then examine two classes of optim izations that can be used to reduce network interface energy consumpti on on these devices: transport-level strategies and application-level strategies. Simulation experiments of transport-level strategies show that the dominant cost comes not from the number of packets sent or re ceived by a particular transport protocol but the amount of lime that the NI is in an active but idle state. Simulation experiments of appli cation-level strategies that significant energy savings can be made wi th a minimum of user-visible latency.