1. A method to determine a clock time difference between a first terminal and a second terminal, the method comprising: receiving an Internet Protocol packet at the first terminal from the second terminal, the packet having a time stamp indicating the time at which it was sent from the second terminal; determining the time at which the packet arrived at the first terminal; comparing the time stamp and the arrival time to determine a minimal feasible bias; comparing the determined minimal feasible bias to a stored bias; setting the stored bias to the determined minimal feasible bias if the stored bias is less than the minimal feasible bias; and determining a clock time difference at the second terminal using the stored bias.