Troubleshooting guide

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Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 5 Troubleshooting DOCSIS Networks
Troubleshooting Slow Peformance
Invalid BW Requests= 0x102
Minislots Requested= 0x65B74A2
Minislots Granted = 0x65B74A2
Minislot Size in Bytes = 16
Map Advance (Dynamic) : 2809 usecs
UCD Count = 23068
In the example above, the estimated SNR reading is 28.628dB. This is adequate for QPSK upstream
operation. Note that the SNR figure given in the output of this command is only an estimate and is
no substitute for an SNR figure derived from a Spectrum Analyzer or other appropriate testing
equipment.
See the Cisco Cable Modem Termination System Command Reference for more information about
the show controller cable X/Y upstream Z command.
• A quickly incrementing number of Corr FEC and Uncorr FEC errors in the output of a show cable
hop command. Corr FEC errors indicates data that was corrupted by upstream noise but was able to
be recovered. Uncorr FEC errors indicate data that was corrupted by upstream noise and was not
able to be recovered resulting in lost data and slower performance.
A sample output from the show cable hop command is show below.
uBR7246-VXR# show cable hop cable 3/0
Upstream Port Poll Missed Min Missed Hop Hop Corr Uncorr
Port Status Rate Poll Poll Poll Thres Period FEC FEC
(ms) Count Sample Pcnt Pcnt (sec) Errors Errors
Cable3/0/U0 25.200 Mhz 34 * * * set to fixed frequency * * * 196 55
Cable3/0/U1 25.200 Mhz 34 * * * set to fixed frequency * * * 1655 160
Cable3/0/U2 25.200 Mhz 34 * * * set to fixed frequency * * * 76525 9790
Cable3/0/U3 25.200 Mhz 34 * * * set to fixed frequency * * * 501 77
Cable3/0/U4 admindown 34 * * * interface is down * * * 0 0
Cable3/0/U5 admindown 34 * * * interface is down * * * 0 0
In the example above, each active upstream port on cable 3/0 seems to have experienced packet loss
due to noise. Upstream port 0 seems to be the least affected and upstream port 2 seems to be the
most heavily affected. The important factor to note is how quickly the FEC Errors are incrementing
rather than the total number of errors.
See the Cisco Cable Modem Termination System Command Reference for more information about
the show cable hop command.
• A high number of "flap" events in the output of a show cable flap-list. The flap statistics that are
most pertinent to possible RF or noise problems are the Miss column, which indicates missed
ranging requests, and the P-Adj column which indicates rapidly varying upstream power levels.
A sample output from the show cable flap-list command is shown below.
uBR7246-VXR# show cable flap-list
MAC Address Upstream Ins Hit Miss CRC P-Adj Flap Time
0000.d025.1b99 Cable3/0/U0 23 58 30 0 *27 77 Oct 23 03:08:23
0002.ddfa.0aa5 Cable3/0/U1 5 518 1260 0 0 131 Oct 23 03:09:43
0001.e659.43bd Cable3/0/U1 541 342 1467 0 0 746 Oct 23 03:09:17
0001.7659.44c7 Cable3/0/U1 0 694 0 0 1 1 Oct 23 01:44:23
0050.9366.22d3 Cable3/0/U1 0 708 0 0 1 1 Oct 23 01:38:14
0001.f659.44e7 Cable3/0/U1 0 701 0 0 1 1 Oct 23 02:25:11
In the example seen above, the cable modem with MAC Address 0000.d025.1b99 has had a number
of P-Adj events. This would typically indicate a bad connection or a faulty reverse path amplifier.
The cable modem with MAC Address 0002.ddfa.0aa5 has a large number of misses as compared to
hits and therefore may be suffering from either downstream or upstream noise issues. The cable
modem with MAC Address 0001.e659.43bd has a high number of insertions, which typically
indicates a severe RF problem, or more likely a provisioning problem.