PeriodicTime is used only to set the 'phase' of the GPS scan. The actual value of PeriodicTime can be arbitrarily far into the past or future. For example, if PeriodicInterval is 86400 (a day) and if PeriodicTime is set to UTC midnight on some day (in the past, present, or future) then periodic GPS scans will occur every day at UTC midnight. These MUST begin on the very next midnight, even if PeriodicTime refers to a day in the future. The Unknown Time value indicates that no particular time reference is specified. That is, the CPE MAY locally choose the time reference, and needs only to adhere to the specified PeriodicInterval. If absolute time is not available to the CPE, its periodic GPS scan behavior MUST be the same as if PeriodicTime parameter was set to the 'Unknown Time' value. The absolute UTC time will be specified as follows (ref: RFC1902): YYYYMMDDHHMMZ, where: YYYY - four digits of year MM - month (01 through 12) DD - day of month (01 through 31) HH - hours (00 through 23) MM - minutes (00 through 59) Z - the character 'Z' denotes Greenwich Mean Time (GMT). For example, '199502192015Z' represents 8:15pm GMT on 19 February 1995. The value of this parameter is not persistent. TR-069/TR-181 reference: Device.FAP.GPS.PeriodicTime.