Configuration - Cisco Catalyst 2000 Configuration Handbook

250 Cisco LAN Switching Configuration Handbook
The switch and phone can communicate over an 802.1Q trunk, with voice traffic in a
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separate voice VLAN ID (VVID). Voice class of service (CoS) information can be
propagated across the trunk.
A Cisco IP Phone performs the following steps during initialization:
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Configuration

(Optional) Detect an inline-powered device:
1.
(interface) power inline {auto | never}
By default, the switch attempts to discover an inline-powered device on a switch
port (auto). Use the off (COS) or never (IOS) keyword to disable inline power detec-
tion.
Caution After a powered device has been detected and power has been applied to a
switch port, the switch waits four seconds to see that the device has initialized and the link
is established. If not, power is removed from the switch port.
If you unplug the powered device within the four-second delay and plug a regular Ethernet
device in its place, power will still be applied, and the device could be damaged. Wait at
least ten seconds before swapping devices on a switch port.
Inline power is detected by the switch, if needed.
The phone triggers a CDP exchange. The actual amount of required power is
sent to the switch, while the VVID number is sent to the phone. The phone can
also receive instructions on how to extend the QoS trust boundary.
A special 802.1Q trunk is negotiated between the phone and the switch, if a
VVID is to be supported. On Catalyst 4000 and 6000 switches, the trunk is
negotiated through Dynamic Trunk Protocol (DTP) messages.
A DHCP request is made.
A DHCP reply is sent to the phone, containing the IP address and TFTP server
address (DHCP option 150).
The TFTP server is contacted for a phone configuration file. A list of Cisco
Unified Communications Manager (CUCM) servers is also obtained.
Registration with a CallManager server is performed. A directory number (DN)
is obtained so that calls can be placed and received.