Patent ID: 7454521

Claim:
A method for determining a bound around a reference time such that the reference time is determined to have occurred between a first bound limit and a second bound limit, the method comprising the steps of: transmitting a protected reference time request from a first computing device to a higher level computing device, wherein the higher level computing device is a level closer to a reference time source; storing a transmittal time, according to a clock of the first computing device, when the protected reference time request was transmitted to the higher level computing device; receiving a response from the higher level computing device at the first computing device, the response comprising a protected reference time source response, the reference time source response comprising the reference time, and a collection of protected reference time requests from each first level computing device that had transmitted the collection of protected reference time requests to the reference time source prior to the reference time; storing a receipt time, according to the clock of the first computing device, when the response from the higher level computing device was received at the first computing device; setting the first bound limit at the transmittal time when the protected reference time request was transmitted to the higher level computing device; and setting the second bound limit at the receipt time when the response from the higher level computing device was received.