4.2 Green Ethernet—Port Power Saving Configuration

The Port Power Saving Configuration page allows you to configure the port power savings features.

EEE is a power saving option that reduces power usage when there is low or no traffic utilization. EEE works by powering down circuits when there is no traffic. When a port gets data to be transmitted all circuits are powered up. The time it takes to power up the circuits is named wakeup time. The default wakeup time is 17 us for 1Gbit links and 30 us for other link speeds.  EEE devices must agree upon the value of the wakeup time in order to make sure that both the receiving and transmitting device has all circuits powered up when traffic is transmitted. The devices can exchange wakeup time information using the LLDP protocol. EEE works for ports in auto-negotiation mode, where the port is negotiated to either 1G or 100 Mbit full duplex mode. For ports that are not EEE-capable the corresponding EEE checkboxes are grayed out and thus impossible to enable EEE for. When a port is powered down for saving power, outgoing traffic is stored in a buffer until the port is powered up again. Because there are some overhead in turning the port down and up, more power can be saved if the traffic can be buffered up until a large burst of traffic can be transmitted. Buffering traffic will give some latency in the traffic.

The Port Power Saving Configuration page has the following parameters:

• Port: The switch port number of the logical port
• ActiPHY: Link down power savings enabled. ActiPHY works by lowering the power of a port if there’s no link. The port is powered up momentarily to determine if the cable is inserted.
• PerfectReach: Cable length power savings enabled. PerfectReach works by determining the cable length and lowering the power for ports with short cables.
• EEE: Controls if EEE is enabled for this switch port.