Method and system for monitoring data flow in an IP network device

User input values define an inspection window for evaluating a desired traffic element portions of a bitstream. Offset and reference values determine the start of the window with respect to the bitstream and values for a filter register and mask registers define the size of the window. As the bitstream 'passes through' the window, the bits in the window are compared to bits in the filter and mask registers. Traffic element portions that match the criteria of the window are stored into a storage device formed with a FPGA. Filter controls that are also formed with, the FPGA determine that the window criteria are met; and send a control signal to a capture apparatus gate to permit the current bitstream portion into a storage device that is also formed with the FPGA. The stored element portions are later evaluated by the CMTS and/or operation personnel.