An apparatus, system and method provides an out-of-synchronization
detection by using a network layer checksum. A process operating at an
upper layer verifies that a checksum embedded in a network layer header
is correct before encrypting and transmitting a data packet containing
the header and a payload. The data packet is received through a wireless
communication channel at a receiver and decrypted. A calculated checksum
is calculated on the received payload at the receiver and compared to the
received checksum embedded in the header. A key stream used at the
receiver for decrypting the received encrypted data packets is determined
to be out of synchronization with a key stream used at the transmitter to
encrypt the data packets if the calculated checksum is not equal to the
network layer checksum.