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3-8 2131-0120 Rev 00
Chapter 4
Troubleshooting
This chapter contains information you can use to troubleshoot LANcity Provisioning
Server (LCn) problems. It includes the following:
" LCP LED sequence definitions
" RF power level measurement
" C/N measurement
" Spectrum analyzer settings
LCP LED Sequence Definitions
The LEDs on the front panel of the Cable Data modem (CDM) indicate the diagnostic that
is currently running. Figure 4-1 illustrates the LEDs.
ETX-CDM is using Ethernet
PWR - Power is on
BTX - CDM is using broadband
BSA - CDM has achieved
block sync
Figure 4-1 CDM Front Panel LEDs
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LCP Network Management Guide
Table 4-1 Illuminated LEDs During Diagnostics
Diagnostic PWR ETX BTX BSA
Low Memory Test x
KSeg0/KSeg1 Cache Test x
Data Cache MATs+ Test x
Instruction Cache MATs+ Test x x
Data Cache Block Refill Test x x
Instruction Cache Block Refill Test x x x
PROM Checksum Test x
Write Buffer Test x x
Memory Test x x
Ethernet Address PROM Checksum Test x x x
UniLINK Address PROM Checksum Test x x
Exception Test x x x
Sonic Registers Test x x
Sonic CAM Test x x x
Sonic Loopback Test x x x
Start Up Operational Code x
Failure Loading/No Application Available x x
RF Power Level Measurement
Radio Frequency (RF) power level measurements can cause problems, particularly on the
network side.
You can use the following tools to troubleshoot the RF portion of the network using
LANcity Management Information Base (MIB) variables:
" Ingress monitoring
" RF amplitude fluctuations
" RF plumbing changes
" Power up patience
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Troubleshooting
Ingress
Ingress, or noise, is the most common problem in any two-way CATV network. Typically,
noise in the network accumulates at the headend and the LANcity Headend (LCh) loses
block sync because the C/I () ratio falls below 25 dB. When the LCh loses block sync, all
the modems on that network also lose block sync and reset. Each time the LCh and
modems lose block sync for between one and two minutes, they reset themselves.
To determine whether the LCh and modems are continuously resetting, review the
Maintenance Summary Group of the LCh (LANcity headend) and the History log to
determine how many times the headend lost block sync since the last reboot.
Reviewing Maintenance Summary Variables
To review Maintenance Summary variables:
1. Access the SNMPc network experiencing the difficulty.
a. On the SNMPc desktop, select the LCh you want to check.
b. Choose Manage>LCP/LCb V3.xx or greater>Monitoring>Mainenance. An Edit
Table Entry window (Figure 4-2) displays the maintenance information for the
LCh.
Figure 4-2 Edit Table Entry Window for Maintenance Summary Information
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LCP Network Management Guide
2. Check the following variables to determine how often the LCh has reset itself:
" Loss Block Sync
" Time-outs Establishing Block Sync
" Bridge Resets
" System Up Time
If the variables show that the LCh has reset more than ten times since it was last reset,
noise at the headend is most likely the problem.
One of the ways to reduce noise at the LCh, is to limit the number of combining segments
to a number that does not relate a signal to noise number less than 25 dB.
RF Amplitude Fluctuations
Cable Data modems (CDMs) are sensitive to RF amplitude fluctuations. They can adjust
to small fluctuations, such as a 3dB change. However, if the fluctuation is greater than
3dB, the CDM resets itself because it can no longer adjust its loop delay level to the level
it is supposed to transmit to itself.
You can determine whether the CDM is operating normally by checking the
AvgLDRxLevel (the level that the modem is transmitting to itself) and the
AvgBSRxLevelDbmv (the transmission level the modem is trying to match) by looking at
the Auto Adjust variables in SNMPc.
To check the Auto Adjust variables
1. Access SNMPc and select the CDM you want to check.
2. Choose Manage>LCP/LCb V3.xx or greater>Auto Adjust. The LCP CATV Info Edit
Table Entry window (4-3) appears.
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Troubleshooting
Figure 4-3 LCP CATV Info Edit Table Entry Window
3. Compare the AvgBSRxLevelDbmv (receive power, block sync level) to the
MinBSrxLevelDbmv and MaxBSRxLevelDbmvs to determine the receive window of
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