CLI Reference Guide-R04

Chapter 11 | Interface Commands
Power Savings
– 443 –
Command Usage
◆ IEEE 802.3 defines the Ethernet standard and subsequent power requirements
based on cable connections operating at 100 meters. Enabling power saving
mode can reduce power used for cable lengths of 60 meters or less, with more
significant reduction for cables of 20 meters or less, and continue to ensure
signal integrity.
◆ Power saving mode only applies to the Gigabit Ethernet ports using copper
media.
◆ Power savings can be enabled on Gigabit Ethernet RJ-45 ports.
◆ The power-saving methods provided by this switch include:
■
Power saving when there is no link partner:
Under normal operation, the switch continuously auto-negotiates to find a
link partner, keeping the MAC interface powered up even if no link
connection exists. When using power-savings mode, the switch checks for
energy on the circuit to determine if there is a link partner. If none is
detected, the switch automatically turns off the transmitter, and most of
the receive circuitry (entering Sleep Mode). In this mode, the low-power
energy-detection circuit continuously checks for energy on the cable. If
none is detected, the MAC interface is also powered down to save
additional energy. If energy is detected, the switch immediately turns on
both the transmitter and receiver functions, and powers up the MAC
interface.
■
Power saving when there is a link partner:
Traditional Ethernet connections typically operate with enough power to
support at least 100 meters of cable even though average network cable
length is shorter. When cable length is shorter, power consumption can be
reduced since signal attenuation is proportional to cable length. When
power-savings mode is enabled, the switch analyzes cable length to
determine whether or not it can reduce the signal amplitude used on a
particular link.
Note: Power savings can only be implemented on Gigabit Ethernet ports using
twisted-pair cabling. Power-savings mode on a active link only works when
connection speed is 1 Gbps, and line length is less than 60 meters.
Example
Console(config)#interface ethernet 1/24
Console(config-if)#power-save
Console(config-if)#