Our major purpose in this study is to develop a method for achieving power conservation with a network itself. The proposed power saving approach takes traffic characteristics of network into consideration. If network switch can adapt its processing speed to arrival traffic rate, power saving can be expected depending on the network utilization. The same idea is already materialized just as Intel's Speedstep technology . We first confirm this consideration by measuring the power consumption of some switches and show that a Giga bit Ethernet port consumes 2 or 3 W with an addition of a link. Based on this experiment, we propose a scheme to achieve the dynamic control of the transmission capacity between switches in order to reduce the power consumption based upon the change in traffic volume. To control the transmission speed dynamically and gradually, Link Aggregation is used in our scheme. From simulation studies, we show that the proposed architecture can achieve both high power saving capability and sufficient feasibility.