If the bits are not repairable the decoder reports an uncorrectable codeword. This means the subscriber's device (PC, iPad, etc.) must re-transmit the data if possible and their QoE will start to diminish as uncorrectable codewords increase. This is especially true for real-time services such as gaming.

How many uncorrectable codewords is acceptable?

The uncorrectable errors are something to be more concerned about because these errors result in lost data. For voice-over-IP (VoIP), the recommended best practice is not to exceed 1% uncorrectable codeword errors.

What causes upstream codeword errors?

If the cable modem is transmitting less than 40 dBmV the carrier-to-noise (CNR) may start to become a problem and degrade upstream SNR (MER). This will increase uncorrectable codeword errors. ... This will also result in uncorrectable codeword errors or even a cable modem that intermittently drops offline.