Cisco 7821 Administration Manual page 20

Phone Power Requirements
Pin number
3
4
5
6
7
8
Note
Phone Power Requirements
The Cisco IP Phone 7821, 7841, and 7861 can be powered with external power or with Power over Ethernet
(PoE). A separate power supply provides external power. The switch can provide PoE through the phone
Ethernet cable.
Cisco IP Phone 7821, 7841, and 7861 Administration Guide for Cisco Unified Communications Manager 10.0
(SIP)
6
Function
BI_DA+
BI_DD+
BI_DD-
BI_DA-
BI_DC+
BI_DC-
BI stands for bidirectional, while DA, DB, DC and DD stand for Data A, Data B, Data C and Data
D respectively.