Configuring Headend Broadband Access Router Features
Configuring the Upstream Cable Interface
MC-546
Cisco IOS Multiservice Applications Configuration Guide
Setting the Upstream Channel Width
Enter the channel width in Hz. Valid values are 200000 Hz (160 kilosymbols per second, or ksps),
400000 Hz (320 ksps), 800000 Hz (640 ksps), 1600000 Hz (1280 ksps), and 3200000 Hz (2560 ksps).
The default is 1600000 Hz.
Note If you change the channel width, the symbol rate changes accordingly (symbol rate =
1.25 * channel width). Higher symbol rates are more susceptible to RF noise and
interference. If you use a symbol rate or modulation format beyond the capabilities of your
HFC network, you might experience packet loss or loss of cable modem connectivity.
Note For QAM-16 channel widths of 400 kHz (320 ksps) or greater, we recommend that you use
16-QAM modulation only for long and short data and that you use QPSK for request,
initial, and station communication. For QAM-16 channel widths of 200 kHz (160 ksps), all
communication must be able to use 16-QAM. That is, 160 ksps with 16-QAM requires an
exceptional SNR in your upstream channel(s). When you use QAM-16 for request, initial,
and station maintenance messages with channel widths greater than 400 kHz, the QAM-16
preamble and message data takes longer to transmit than the QPSK format.
To set the upstream channel width, use the following command in cable interface configuration mode:
Verifying Upstream Channel Width
To verify the current value of the upstream channel width, enter the show controllers cable command
for the upstream port you just configured:
CMTS01# show controllers cable 6/0 u0
Cable6/0 Upstream 0 is up
Frequency 24.016 MHz, Channel Width 0.800 MHz, QPSK Symbol Rate 0.640 Msps
Spectrum Group is overridden
SNR 33.2560 dB
Nominal Input Power Level 0 dBmV, Tx Timing Offset 2288
Ranging Backoff automatic (Start 0, End 3)
Ranging Insertion Interval automatic (60 ms)
Tx Backoff Start 0, Tx Backoff End 4
Modulation Profile Group 1
Troubleshooting Tips
To troubleshoot the configuration, perform the following tasks:
• Use a valid combination of modulation format (QPSK/QAM-16), minislot size, frequency, and the
no shutdown command.
Command Purpose
Step 1
CMTS01(config-if)# cable upstream usport
channel-width width
Sets the upstream channel width for your upstream
RF carrier in Hz.
Step 2
CMTS01(config-if)# no cable upstream usport
channel-width
Returns the channel width to its default setting of
1600000 Hz.
