A cable modem termination system (100, 520), comprising: a memory, on which instructions are stored; and a processor configured to execute instructions stored on the memory to execute at least the following processing: determining a first quantity related to uncorrectable erroneous codewords and a second quantity related to other codewords except the erroneous codewords in a data packet received by the cable modem termination system (100, 520) from a modem via a channel; calculating a first metric relating the first quantity to the second quantity; and in response to the first metric exceeding a first threshold for a first predetermined time, determining the channel as a damaged channel; wherein the cable modem termination system (100, 520) is characterized in that the processor is further configured to execute instructions stored on the memory to perform at least the following processing: determining a third quantity related to uncorrectable erroneous test codewords and a fourth quantity related to other test codewords except the erroneous test codewords in test data received by the cable modem termination system (100, 520) from the modem via the channel; calculating a second metric relating the third quantity to the fourth quantity; and in response to the second metric being lower than a second threshold for a second predetermined time, determining the channel as an available channel. a memory, on which instructions are stored; and a processor configured to execute instructions stored on the memory to execute at least the following processing: determining a first quantity related to uncorrectable erroneous codewords and a second quantity related to other codewords except the erroneous codewords in a data packet received by the cable modem termination system (100, 520) from a modem via a channel; calculating a first metric relating the first quantity to the second quantity; and in response to the first metric exceeding a first threshold for a first predetermined time, determining the channel as a damaged channel; wherein the cable modem termination system (100, 520) is characterized in that the processor is further configured to execute instructions stored on the memory to perform at least the following processing: determining a third quantity related to uncorrectable erroneous test codewords and a fourth quantity related to other test codewords except the erroneous test codewords in test data received by the cable modem termination system (100, 520) from the modem via the channel; calculating a second metric relating the third quantity to the fourth quantity; and in response to the second metric being lower than a second threshold for a second predetermined time, determining the channel as an available channel. determining a first quantity related to uncorrectable erroneous codewords and a second quantity related to other codewords except the erroneous codewords in a data packet received by the cable modem termination system (100, 520) from a modem via a channel; calculating a first metric relating the first quantity to the second quantity; and in response to the first metric exceeding a first threshold for a first predetermined time, determining the channel as a damaged channel; wherein the cable modem termination system (100, 520) is characterized in that the processor is further configured to execute instructions stored on the memory to perform at least the following processing: determining a third quantity related to uncorrectable erroneous test codewords and a fourth quantity related to other test codewords except the erroneous test codewords in test data received by the cable modem termination system (100, 520) from the modem via the channel; calculating a second metric relating the third quantity to the fourth quantity; and in response to the second metric being lower than a second threshold for a second predetermined time, determining the channel as an available channel. determining a third quantity related to uncorrectable erroneous test codewords and a fourth quantity related to other test codewords except the erroneous test codewords in test data received by the cable modem termination system (100, 520) from the modem via the channel; calculating a second metric relating the third quantity to the fourth quantity; and in response to the second metric being lower than a second threshold for a second predetermined time, determining the channel as an available channel.