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Chapter 2
Cisco CMTS Configuration Commands
Changing the DOCSIS Mode for an Upstream Port Forces the Cable Modems on That Upstream to Go Offline and
Reregister
When you switch the DOCSIS mode of an upstream between the TDMA-only, mixed TDMA/A-TDMA,
and A-TDMA-only modes, cable modems that are currently online on that upstream are taken offline
and are forced to reregister, so that the CMTS can determine the capabilities of the cable modems on the
new channels.
If you change an upstream port to A-TDMA only mode, DOCSIS 1.x cable modems will not be able to
come online on that upstream. If you change an upstream to TDMA only mode, DOCSIS 2.0-compliant
cable modems are expected to attempt to come online on another upstream that is configured for A-
TDMA or mixed mode. If no such upstreams are configured, or if the cable modem is configured to use
only that particular upstream, it comes online in DOCSIS 1.x mode.
DOCSIS 2.0-capable cable modems that are already online on a TDMA-only upstream do not
Note
automatically reregister on another upstream that has been configured for mixed-mode or A-TDMA-only
operations. The cable modem must either be reset or the CMTS must send an Upstream Channel Change
(UCC) message to instruct the cable modem to move to the new channel.
If you change an upstream port to the mixed TDMA/A-TDMA mode, and some cable modems remain
offline, or appear to come online but cannot pass traffic, upgrade the modem software to a DOCSIS-
compliant software version.
The cable physical plant must support the higher upstream bandwidths and symbol rates to be able to
Note
use the A-TDMA or mixed mode modulation profiles.
Examples
The following example shows how to configure the first four upstreams for the first downstream on the
Cisco uBR-MC28U/X cable interface line card in slot 5/0. The first two upstreams are configured for A-
TDMA mode and the last two upstreams are configured for mixed TDMA/A-TDMA mode.
Router# config terminal
Router(config)# interface cable 5/0/0
Router(config-if)# cable upstream 0 docsis-mode atdma
%%Docsis mode set to ATDMA only, 1.x CMs will go offline.
%%The following defaults will be set:
%%Channel Width 6.4MHz
%%Minislot Size 1 tick
%%Modulation Profile 241
Router(config-if)# cable upstream 1 docsis-mode atdma
%%Docsis mode set to ATDMA only, 1.x CMs will go offline.
%%The following defaults will be set:
%%Channel Width 6.4MHz
%%Minislot Size 1 tick
%%Modulation Profile 241
Router(config-if)# cable upstream 2 docsis-mode tdma-atdma
%%Docsis mode set to DOCSIS2.0 Mixed Mode.
Router(config-if)# cable upstream 3 docsis-mode tdma-atdma
%%Docsis mode set to DOCSIS2.0 Mixed Mode.
Router(config-if)# exit
Router(config)# exit
Router#
OL-1581-08
Cisco Broadband Cable Command Reference Guide
cable upstream docsis-mode
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