Phone Startup Process
When connecting to the VoIP network, the Cisco Unified IP Phones go through a standard startup process, described in the following steps. Depending on your specific network configuration, not all of these steps may occur on your Cisco Unified IP Phone.
Obtain ower from the switch If a phone is not using external power, the switch provides in-line power through the Ethernet cable attached to the phone.
Load the stored phone image The Cisco Unified IP Phone has non-volatile Flash memory in which it stores firmware images and user-defined preferences. At startup, the phone runs a bootstrap loader that loads a phone image stored in nonvolatile flash. Using this image, the phone initializes its software and hardware.
Configure VLAN If the Cisco Unified IP Phone is connected to a Cisco Catalyst switch, the switch next informs the phone of the voice VLAN defined on the switch. The phone needs to know its VLAN membership before it can proceed with the Dynamic Host Configuration Protocol (DHCP) request for an IP address.
Obtain an IP address If the Cisco Unified IP Phone is using DHCP to obtain an IP address, the phone queries the DHCP server to obtain one. If your network does not use DHCP, you must assign static IP addresses to each phone locally.
Access a TFTP server
In addition to assigning an IP address, the DHCP server directs the Cisco Unified IP Phone to a TFTP Server. If the phone has a statically defined IP address, you must configure the TFTP server locally on the phone; the phone then contacts the TFTP server directly.
Note You can also assign an alternative TFTP server to use instead of the one assigned by DHCP.
Request the CTL file
The TFTP server stores the certificate trust list (CTL) file. This file contains the certificates necessary for establishing a secure connection between the phone and Cisco Unified Communications Manager.
For more information, see Cisco Unified Communications Manager Security Guide, “Configuring the Cisco CTL Client” chapter.
Request the ITL file.
The phone requests the ITL file after it requests the CTL file. The ITL file contains the certificates of the entities that the phone can trust. The certificates are used for authenticating a secure connection with the servers or authenticating a digital signature signed by the servers.
For more information, see Cisco Unified Communications Manager Security Guide, “Security by Default” chapter.
Request the configuration file
The TFTP server has configuration files, which define parameters for connecting to Cisco Unified Communications Manager and other information for the phone.
Contact Cisco Unified Communications Manager
The configuration file defines how the Cisco Unified IP Phone communicates with Cisco Unified Communications Manager and provides a phone with its load ID. After obtaining the file from the TFTP server, the phone attempts to make a connection to the highest priority Cisco Unified Communications Manager on the list. When security is implemented, if the security profile of the phone is configured for secure signaling (encrypted or authenticated), and the Cisco Unified Communications Manager is set to secure mode, the phone makes a TLS connection. Otherwise, it makes a nonsecure TCP connection.
If the phone was manually added to the database, Cisco Unified Communications Manager identifies the phone. If the phone was not manually added to the database and auto-registration is enabled in Cisco Unified Communications Manager, the phone attempts to auto-register itself in the Cisco Unified Communications Manager database.
Autoregistration is disabled when you configure the CTL client. In this case, the phone must be manually added to the Cisco Unified Communications Manager database.