Cisco 7821 Installationshandbuch - Seite 39

Phone Power Requirements

Power Outage

Your access to emergency service through the phone requires that the phone receive power. If a power interruption

occurs, service or emergency calling service dialing does not function until power is restored. If a power failure or

disruption occurs, you may need to reset or reconfigure the equipment before you can use service or emergency calling

service dialing.

You can reduce the amount of energy that the Cisco IP Phone consumes by using Power Save mode.

In Power Save mode, the backlight on the screen is not lit when the phone is not in use. The phone remains in Power

Save mode until the user lifts the handset or presses any button. Set up each phone to enable or disable Power Save

settings.

Note

Cisco IP Phones 6821 and 7811 and Cisco IP Conference Phones 7832 and 8832 don't support

Power Save Mode.

The phone and the switch negotiate the power that the phone consumes. Cisco IP Phones operate at multiple power

settings, which lowers power consumption when less power is available.

After a phone reboots, the switch locks to one protocol (CDP or LLDP) for power negotiation. The switch locks to the

first protocol (containing a power Threshold Limit Value [TLV]) that the phone transmits. If the system administrator

disables that protocol on the phone, the phone cannot power up any accessories because the switch does not respond to

power requests in the other protocol.

We recommend that you always enable Power Negotiation (default) when connecting to a switch that supports power

negotiation.

If Power Negotiation is disabled, the switch may disconnect power to the phone. If the switch does not support power

negotiation, disable the Power Negotiation feature before you power up accessories over PoE. When the Power

Negotiation feature is disabled, the phone can power accessories up to the maximum that the IEEE 802.3af-2003

standard allows.

Note

• When CDP and Power Negotiation are disabled, the phone can power accessories up to

15.4W.

• Cisco IP Phones 6841 and 6861 don't support the Power Negotiation over LLDP feature.

Installation Guide for Cisco IP Phone with Multiplatform Firmware

Technical Details