A method of transmitting or retransmitting a packet in a communication system. The hardware device handles certain functions in hardware, thereby permitting the microprocessor at the lighting device to incur substantially less processing load. When used with a previously known blood handling system, the present filter apparatus facilitates priming and the addition of additional blood handling elements during operation of the blood handling system. When the truck door is open, the strap can be pulled to a desired length and held at that desired length.