A backflow prevention apparatus and method are provided for use in irrigation systems. The constellation provides time-continuous visibility with at least one satellite to any point above 25 North latitude. The method further includes transferring the packet to a receive ring associated with the VNIC, wherein the RR is located on the NEM, providing the network express manager with a receive descriptor, transferring the packet to the guest OS memory using the receive descriptor, and notifying the guest OS that the packet is in the guest OS memory. In a deterministic phase, compressed deterministic test patterns from an external tester are applied to the decompressorPRPG. The mattress is supported on slats mounted between the stringers.