![]() DHCP options include items such as default gateway, DNS server information, domain name information, and so on. When the Cisco IP Phone accepts the offer, it receives all the DHCP options that go along with the DHCP request. The DHCP server responds with an IP address offer.The Cisco IP Phone sends a DHCP request asking for an IP address on its voice VLAN.The Cisco IP Phone now knows what VLAN it should use. As the Cisco IP Phone powers on, the Cisco switch delivers voice VLAN information to the IP phone using CDP as a delivery mechanism.If the IP phone and switch support PoE, the IP phone receives power through either Cisco-proprietary PoE or 802.3af PoE. The Cisco IP Phone connects to an Ethernet switchport. ![]() Here is the Cisco IP Phone boot process, start to finish: ![]() By understanding the IP Phone boot process, you can more fully understand how the Cisco IP Phone operates (which aids significantly in troubleshooting Cisco IP Phone issues). Now that you learned about the VLAN architecture used with Cisco IP Phones, we can turn our attention to the IP Phones themselves. > IP Phone downloads softkey template from CUCM.Understanding the Cisco IP Phone Boot Process > Call Processing Server ( CUCM or CME) checks the database for the MAC address of the requested IP Phone to send the operating configuration if the MAC address is available. > If the IP Phone finds active call processing server in the list, it registers to the server by using SIP ( Open Standard) or SCCP protocol. This process continues until the IP phone registers successfully or the list of call processing agents is exhausted. > If this fails, the IP phone moves to the next server in the configuration file. > The Cisco IP phone then attempts to contact the first call processing server (the primary server) listed in its configuration file to register. > If the IP Phone needed to upgrade its software then it downloads the firmware from TFTP Server. Included in the configuration file is a list of valid call processing agents ( CUCM or CME). ![]() > After the Cisco IP phone has the IP address of the TFTP server, it contacts the TFTP server and downloads its configuration file. ![]()
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