Troubleshooting guide

7-38
Cisco Broadband Local Integrated Services Solution Troubleshooting Guide
OL-5169-01
Chapter 7 Troubleshooting the CMTS
Troubleshooting the Cisco uBR7246VXR
Generating PRBS Test Signals
To configure Pseudo Random Bit Stream (PRBS) test signals, perform the steps in Table 7-6 in the
configure interface mode.
Verifying Test Signal Output
To verify the output of a continuous-wave test signal or the output of a PRBS test signal, use a spectrum
analyzer on the downstream channel. The downstream carrier is enabled as a default.
The standard mode of operation is modulated signal output and the interface is active. For PRBS and
continuous wave output, the selected interface will be shut down.
The functioning of the no cable downstream if-output command has not changed. The interface is shut
down.
Displaying Per-SID Counters for Bandwidth Requests
Data transport over the RF link uses the registered SID address, rather than the Ethernet address. This
allows multiple hosts to access the network by using a single cable modem.
To display per-SID counters for bandwidth requests, use the following command in the privileged EXEC
mode:
show interface cable interface sid sid counters verbose
The show int cx/y sid command displays more complete Service ID (SID) status information.
Sample outputs:
The following command displays sample output for the verbose keyword extension for SID 1 on
interface cable slot 3, port 0:
router# show interface c3/0 sid 1 counters
verbose
Table 7-6 Procedure to Generate PRBS Test Signals
Step Command Description
1 Router(config-if)#
cable downstream if-output prbs
Generates a PRBS test signal on the
downstream channel. The interface is shut
down.
2 Router(config-if)#
no cable downstream if-output
Stops sending test signals.
Note Remember to re-enable the
interface to resume normal
operations.
Sid : 1
Input packets : 39
Input octets : 15964
Output packets : 30
Output octets : 8796
BW requests received : 40
Grants issued : 40
Rate exceeded BW request drops : 0
Rate exceeded DS packet drops : 0