Specifications

Determining RF or Configuration Issues On the
CMTS
Introduction
Before You Begin
Conventions
Prerequisites
Components Used
RF Plant Troubleshooting Rules
Cable Show Commands for RF Problems
DOCSIS Cable Upstream RF Specifications
DOCSIS Cable Downstream RF Specifications
Notes for Tables
Checking the Downstream
Checking the Upstream
Using the Flap List for Diagnosing RF Problems
Related Information
Introduction
This document describes the troubleshooting steps to determine whether a cable network problem is in a cable
router or an RF plant issue. The majority of RF plant issues are diagnosed by low upstream Signal to Noise
Ratio (SNR) level, hence heavy emphasis is placed on examining this value. Initially the document states
some simple rules to follow, together with an explanation of how the upstream SNR level is calculated. It then
illustrates the major configuration parameters and commands to use to verify the downstream and upstream
channels. It finishes with an explanation of the flap list command to further diagnose RF issues.
Using a spectrum analyzer for troubleshooting the RF plant is beyond the scope of this document. If the SNR
level or other analysis points towards an RF plant issue and you wish to troubleshoot this area further using a
spectrum analyzer, then refer to the Connecting and Configuring the Cable Headend in the related information
section.
All uBR7100, uBR7200, and uBR10000 models, and NPE cards with different Cable Cisco IOS® Software
versions follow the same principle in troubleshooting whether this is an RF issue or not. The only difference
may be some command syntax changes and performance capabilities, and the fact that the uBR7100 has an
integrated upconverter.
Before You Begin
Conventions
For more information on document conventions, see the Cisco Technical Tips Conventions.
Prerequisites
This document assumes that the reader has access to a Cisco uBR9xx or CVA120 series cable modem to assist
in their troubleshooting.
Cisco − Determining RF or Configuration Issues On the CMTS