A method for testing the upstream channel of a cable modem system, using a tester, which generates and transmits a known test pattern to the Cable Modem Termination System (CMTS). If there are errors in the packet resulting from the upstream channel, the CMTS discards the packet based on standard Internet Protocol. If there are no errors the packet is returned on the downstream channel to the tester. The tester counts all returned test packets received including test packets with errors resulting in the downstream. Packets with errors are not discarded, but are checked for a portion of the repeating test pattern and checked for the correct number of bits of a test packet. All packets determined to be test packets, including those with errors, are counted over a period of time and compared to the number of packets originally sent.