Juniper Networks G10 CMTS manual CMTS, which reduces the cable modem throughput

HFC Plant Related Issues

•Cable Modem Throughput is Slow

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•	If the throughput of a cable modem seems slow, the cause might be one or more of the
•	following:
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•	! HFC plant issues, such as impulse noise or ingress, that corrupt upstream burst
•	transmissions from the cable modem. A high CERavg value or a low MERavg value in the
•	flap list is indicative of this. Uncorrectable codewords cause packets to be dropped by
•	the CMTS, which reduces the cable modem throughput.
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•	If the CER value is high, but the CERavg value is low, this suggests that burst noise is
•	occurring, but its duration is too short to render a codeword uncorrectable. However, you
•	should investigate the source of the noise as part of your preventive HFC plant
•	maintenance routine.
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•	! HFC plant issues, such as impulse noise, that corrupt downstream transmissions to the
•	cable modem. Increasing the depth of the interleaver can increase the amount of burst
•	protection in the downstream. For example, the default interleaver depth using 64QAM
•	modulation provides 5.9 microseconds of burst protection. You can increase the burst
•	protection to 12, 24, 47, or 95 microseconds. Be aware that increasing the interleaver
•	depth increases the latency of the transmission.
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•	In general, a number of HFC-related issues can be responsible for the receipt of uncorrectable
•	codewords at the CMTS. Table 45 on page 143 describes how to associate flap list statistics to
•	the presence of these issues.
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•	Issuing one or more of the following commands can provide you with additional insight into
•	HFC-related issues that affect cable modem performance:
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•	! show cable modem errors
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•	! show cable modem flap
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•	! show cable modem physical-statistics
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•	! show cable modem remote-query
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158 JUNOSg 3.0 G10 CMTS Hardware Guide