Extension of Phone Power Saving Measures: Backlight on Only During Core Working Hours

The University Computer Center also wants to contribute to the university-wide efforts to save energy. Unfortunately, many of our systems have to offer 24/7 availability and therefore cannot switch to an energy-saving mode. Measures to reduce power consumption have already been successfully implemented in the past for publicly accessible computers, for example in the training pools.

The Cisco Voice-over-IP telephony is one of the last systems, where further possibilities for energy saving exist. Chemnitz University of Technology currently operates 4000 telephones of different generations with a power requirement of 6 watts for older Cisco telephones and less than 3 watts for the new Cisco 7811 and Cisco 8851 devices.

All Cisco phones with a screen backlight offer a sleep mode that turns off the screen backlight. During sleep mode, the phone is still fully operational, allowing you to make and receive phone calls. However, the power requirement is reduced by 10% to 20% during this time.

You can tell that a device is in sleep mode when the screen is off, but a normally unlit button near the screen is lit. On a Cisco 8851, the ring below the screen is illuminated as shown in the picture, on a Cisco 7945 and 7965 this is the button on the lower right edge of the screen.

We have reduced the times when the phone screen is always active to the core working hours of Monday – Friday, 9:00 – 15:00. Outside this time window, the phone goes into sleep mode. However, as soon as a call comes in, you lift the handset or press a key, and the screen backlight is automatically reactivated. A woken phone will automatically go back to sleep after 60 minutes of inactivity.

During the TU Chemnitz closure period at the turn of the year 2022/23, the phones will also be put into deep sleep mode. In this mode, the phones require less than 1 watt, but can no longer receive calls. Parallel calling as well as call forwarding are not affected by the phones’ deep sleep mode. To wake up the phones and make them ready to receive again, one of the keys on the left/right of the screen must be pressed.

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