An Initial Performance Evaluation of Rapid PHY Selection (RPS) for Energy Efficient Ethernet

The IEEE 802.3 energy efficient Ethernet (EEE) study group is considering rapid PHY Selection (RPS) as a mechanism to quickly switch the data rate of an Ethernet link to match link data rate with link utilization. When switching the data rate, RPS causes a momentary disruption of the link. This disruption may cause packet loss due to buffer overflow in upstream switches. We emulate RPS using PAUSE flow control and experimentally study the possible effects of RPS on TCP and UDP file transfer. We show that RPS has little or no perceivable effect on performance, but has some subtle effects on TCP throughput if PAUSE flow control is enabled in the file server.