Troubleshooting guide

BSR Troubleshooting Guide
4-48
Table 4-3 describes how to interpret flap list statistics:
Table 4-3 Flap List Statistic Interpretations
Field Description
Hit and Miss The HIT and MISS columns are keepalive polling statistics between
the BSR and the CM. The station maintenance process occurs for
every CM approximately every 10 seconds. When the BSR receives a
response from the CM, the event is counted as a Hit. If the BSR does
not receive a response from the CM, the event is counted as a Miss. A
CM will fail to respond either because of noise or if it is down. CMs
which only log Misses and zero Hits are assumed to be powered off.
Misses are not desirable since this is usually an indication of a return
path problem; however, having a small number of misses is normal.
The flap count is incremented if there are M consecutive misses where
M is configured in the cable flap miss-threshold parameter. The
parameter value ranges from 1-12 with a default of 6.
Ideally, the HIT count should be much greater than the Miss counts. If
a CM has a HIT count much less than its MISS count, then registration
is failing. Noisy links cause the MISS/HIT ratio to deviate from a
nominal 1% or less. High Miss counts can indicate:
• Intermittent upstream possibly due to noise
• Laser clipping
• Common-path distortion
• Ingress or interference
Too much or too little upstream attenuation
P-Adj The station maintenance poll in the BSR constantly adjusts the CM
transmit power, frequency, and timing. The Power Adjustments
(P-Adj)column indicates the number of times the CM’s power
adjustment exceeded the threshold value. The power adjustment
threshold may be set using the <cable flap power threshold >
parameter with a value range of 0-10 dB and a default value of 2 dB.
Tuning this threshold is recommended to decrease irrelevant entries in
the flap list. Power Adjustment values of 2 dB and below will
continuously increment the P-Adj counter. The CM transmitter step
size is 1.5 dB, whereas the headend may command 0.25 dB step
sizes. Power adjustment flap strongly suggests upstream plant
problems such as:
• Amplifier degradation
• Poor connections
• Thermal sensitivity
Attenuation problem