Information Technology Reference
In-Depth Information
Chapter 3, “Understanding the Cisco IP Phone Concepts and Registration,” and Chapter 4,
“Getting Familiar with CME Administration,” put configurations in place that are key to a
working CME system. It is wise to take a high-level review of these concepts before you
jump into the configuration of the IP phones.
Just about all the concepts discussed so far focus on the boot process of the Cisco IP Phone.
The following list outlines the Cisco IP Phone boot process, which is illustrated in Figure 5-1:
1.
The 802.3af PoE switch sends a small DC voltage on the Ethernet cable, detects an
unpowered 802.3af device, and supplies power to the line.
2.
The switch delivers voice VLAN information to the Cisco IP Phone using Cisco Dis-
covery Protocol (CDP).
3.
The IP Phone sends a Dynamic Host Configuration Protocol (DHCP) request on its
voice VLAN. The DHCP server replies with IP addressing information, including
DHCP Option 150, which directs the IP phone to the TFTP server.
4.
The IP phone contacts the TFTP server and downloads its configuration file and
firmware.
5.
Based on the IP address listed in the configuration file, the IP phone contacts the call
processing server (the CME router, in this case), which supports VoIP functions.
Key
To p i c
CME Router
DHCP Server
TFTP Server
V
1
2
3
4
5
Cisco IP Phone
Figure 5-1
Cisco IP Phone Boot Process
