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Configuring Headend Broadband Access Router Features
Configuring the Downstream Cable Interface
MC-538
Cisco IOS Multiservice Applications Configuration Guide
Setting the Downstream Channel ID
To assign a numeric channel ID to the downstream port on the Cisco cable modem card, use the following
command in cable interface configuration mode:
Verifying the Downstream Channel ID
To verify the downstream channel ID, enter the show controllers cable command for the downstream
port you have just configured:
CMTS01# show controllers cable 6/0 downstream
Cable6/0 Downstream is up
Frequency=96000000, Channel Width 6 MHz, 64-QAM, Symbol Rate 5.056941 Msps
FEC ITU-T J.83 Annex B, R/S Interleave I=32, J=4
Troubleshooting Tips
To troubleshoot the configuration, perform the following tasks:
• Make sure the cable connections are not loose or disconnected.
• Make sure the Cisco cable modem card is firmly seated in its chassis slot and the captive installation
screws are tight.
• Make sure you entered the correct slot and port numbers when you typed the command.
• Make sure the downstream carrier is active by entering the cable downstream if-output command.
Setting the Downstream MPEG Framing Format (Annex B)
The Moving Pictures Experts Group (MPEG) framing format must be compatible with your local
standards and specifications for downstream MPEG framing. Annex B is the DOCSIS MPEG framing
format standard for North America; Annex A is the European standard.
In Cisco IOS Release 12.1, only the Annex B MPEG framing format is supported.
Note The cable modem card downstream ports and the cable modems on the HFC network
connected through these ports must be set to the same MPEG framing format.
To set the downstream MPEG framing format, use the following command in cable interface
configuration mode:
Command Purpose
CMTS01(config-if)# cable downstream channel-id id
Specifies the downstream channel ID. Acceptable range is
0 to 255.
Command Purpose
CMTS01(config-if)# cable downstream annex B
Sets the downstream MPEG framing format.