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The changes of the low power modes of the Open flow Switch will create Delay Time. To ensure the transmission of data and quality of packets, routing algorithms and appropriately mechanisms should be proposed follow Delay Time.
In a recent paper by author Dr. T. H. Vu, two new sleep modes were defined for Openflow Switch to save power consumption. Sleep Port mode which is used to turn off one or more Ethernet port when there is no traffic flowing through the ports. In this mode, the switch is running at 125 MHz in order to maintain the operation of other Ethernet ports. Sleep Switch mode which is activated when there is not any traffic going through any Ethernet port. In this case, the switch does not need to process the data flow and can be running at the minimum clock frequency of 3.90625 MHz, while three out of the four Ethernet ports are completely turned off. In this mode, switch still maintains the operation of one Ethernet port at 10Mbps so that the switch can be waken-up immediately to normal operation.
In other paper, Dr. T. H. Vu also suggested the new method that implemented a new Wakeup on LAN (WOL) function for OpenFlow Switches. In this method, an Ethernet port or a switch can auto-wake up when they receive a broadcast packet (WOL packet) from other devices in the network.
“To ensure the transmission of data and quality of packets when the switch is waken-up from low power modes, Delay Time should be measured and calculated carefully” Dr. T. H. Vu said.
In the paper, T. H. Vu shows how Delay Time measures for WOL method of Openflow Switch and builds the test-bed system for his experiments.
Delay time of waking up the Ethernet port (DTWP) or changing the Ethernet port state from 10Mpbs to 1Gbps (DTCP) is defined from the time when the switch receives WOL packet to the time when data packets are transferred. To verify the time when data packets are transferred through switches, Dr. T. H. Vu found out the signal gmii_rx_dv at rgmii_io block. The gmii_rx_dv signal (Reveive Data Valid) is driven by the PHY to indicate the PHY is presenting recovered and decoded data on the RXD. It is asserted during the entire data frame, and so provides an envelope signal for a valid data frame. When rx_dv = 1 the data frame pass through the Ethernet port, and rx_dv = 0 when port is turned off.
To measure delay time of waking up the Ethernet port (DTWP), Dr. T. H. Vu builds two counters, a counter is activated before waking up the Ethernet port, and a counter is activated after waking up the Ethernet port. DTWP is the average value of two counters. The counters will be stopped if the signal rx_dv = 1. To measure the delay time of changing the Ethernet port state from 10Mpbs to 1Gbps (DTCP), Dr. T. H. Vu also builds a counter. However, rx_dv = 0 when the port is turned off while rx_dv = 1 at several times when it operates at 10Mpbs. Therefore, the parameter -window is defined between the maximum IPG and DTCP. Where IPG is the interpacket gap, which is the time between transmissions of Ethernet packets.
From his design and experiments, delay time of waking up the Ethernet port (DTWP) is approximately 1.8 second while delay time of changing the Ethernet port state from 10Mpbs to 1Gbps (DTCP) is around 1.73 second. The time is to configure PHY blocks as Setup Pll, Auto-MDIX or Auto Negotiation.
In the future, Dr. T. H. Vu will research and propose remedies to improve delay time for WOL method of OpenFlow Switch. He will implement this solution to measure and evaluate delay time for OpenFlow Switch based on NetFPGA-10G.
Dr T. H. Vu, Danang College of Technology, The University of Danang, Vietnam.
A paper about the study appeared recently in Journal of Electrical and Electronic Engineering