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Cisco Unified IP Phone 8961, 9951, and 9971 Administration Guide for Cisco Unified Communications Manager 8.5 (SIP)
OL-20861-01
Chapter 2 Preparing to Install the Cisco Unified IP Phone on Your Network
Providing Power to the Cisco Unified IP Phone
• Display on Duration—Indicates the length of time that the backlight is active once the backlight is
enabled by the programmed schedule
• Display Idle Timeout—Defines the period of user inactivity on the phone before the backlight is
turned off.
Power Negotiation over LLDP
The phone and the switch negotiate the power that the phone can consume. Cisco Unified IP Phone 8961,
9951, 9971 operate at multiple power settings, which lowers their consumption when less power is
available.
After a phone reboots, the switch locks to one protocol (CDP or LLDP) for power negotiation. It 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, it cannot power up any accessories because the
switch does not respond to power requests in the other protocol.
Cisco recommends that Power Negotiation always be enabled (default) when connecting to a switch that
supports power negotiation.
If disabled, the switch may disconnect power to the phone. If the switch does not support power
negotiation, then disable the Power Negotiation feature before you power up accessories over PoE.
When the Power Negotiation feature is disabled, the phone can power the accessories up to 12.9W.
Note When CDP and Power Negotiation are disabled, the phone can power the accessories up to 15.4W.
To enable or disable power negotiation, see Table 8-1, “Telephony Features for the Cisco Unified IP
Phone”.
Obtaining Additional Information About Power
For related information about power, refer to the documents shown in Table 2-2. These documents
provide information about the following topics:
• Cisco switches that work with Cisco Unified IP Phones
• The Cisco IOS releases that support bidirectional power negotiation
• Other requirements and restrictions regarding power
Table 2-2 Related Documentation for Power
Document Topics URL
Cisco Unified IP Phone Power
Injector
http://www.cisco.com/en/US/products/ps6951/index.html
PoE Solutions http://www.cisco.com/en/US/netsol/ns340/ns394/ns147/ns412/net
working_solutions_package.html
Cisco Catalyst Switches http://cisco.com/en/US/products/hw/switches/index.html
Integrated Service Routers http://www.cisco.com/en/US/products/hw/routers/index.html
Cisco IOS Software http://www.cisco.com/en/US/products/sw/iosswrel/products_ios_
cisco_ios_software_category_home.html