Chapter
3: Web Management
Green Ethernet - Port Power Savings
NGSME48T4H Switch User Manual | 36
3.1.2.2. Green Ethernet - Port Power Savings
EEE is a power saving option that reduces the 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.