Performance Analysis of Energy Saving Scheme with Extra Active Period for LAN Switches

A huge number of LAN switches are currently in use worldwide, so ways in which they can save energy are of great practical interest. A simple way to save power is to switch the interface to sleep mode when no packets are buffered, and to keep it in active mode while there are packets to be transmitted. This would appear to be the most effective energy saving scheme. However, mode switching gives rise to an in-rush current, which causes electrical damage to devices. This problem arises from over-frequent mode switching, which should be avoided. Thus, the main objective is to develop a way to reduce the number of mode switchings that result in quite short duration sleep modes, as these do not contribute so much to energy saving but lead to damage to the device. To this end, a method is adopted which keeps the interface in active mode for an extra period after all packets are flushed out from the buffer; this is the "extra active period". This scheme protects the device at the expense of energy saving efficiency. In this paper, the scheme is evaluated analytically in terms of its power reduction ratio and the frequency of mode changes, by modifying the M/M/1 and IPP/M/1 queuing models. The numerical results show how the duration of the extra active period degrades the energy saving performance while successfully reducing the number of mode changes. These results will enable LAN switches to be designed with energy saving in mind yet within the constraints of device characteristics.