This is the name of a valid file stored on the TFTP server which contains the tone definitions. A missing or invalid file name will cause a failure in the configuration of this entry. If this entry points to a build-in tone plan predefined in firmware, then this name will be: 'BUILTIN'. Provisionable file names are not allowed to have the string 'BUILTIN' as their names. This field may be from 1 to 32 alphabetic, numeric, or underscore characters (no embedded spaces) long for a valid entry. A NULL entry will consist of a single space character of length one.