If TFTP server does not contain IP phone configuration file (.e.g., SEP0015C5AABBDD.cnf.xml), the TFTP server returns “Read Error” to the IP Phone
IP phone will then download XmlDefault.cnf.xml from the TFTP server.
IP phone will update its firmware based on the phone load information defined in the configuration file.
IP phone will then register to the CUCM server configured for auto registration defined in XmlDefault.cnf.xml.
CUCM will automatically create a phone device record in the database and assign a DN from the configured auto registration range to the first line of the device and then create the configuration file (SEP0015C5AABBDD.cnf.xml).
IP phone will then download the configuration file (SEP0015C5AABBDD.cnf.xml) and register to the CUCM.