Configuring Headend Broadband Access Router Features
Operations and Provisioning Features
MC-531
Cisco IOS Multiservice Applications Configuration Guide
Downstream Channel ID Configuration
Downstream channel ID configuration allows all cable modems on the HFC network to identify
themselves via unique downstream channel IDs instead of their downstream frequencies. Cable modems
communicate their downstream ID when making a connection, not their downstream frequency. This
feature allows system administrators to enter a configurable downstream channel ID to a value other than
the default. Thus, each downstream channel ID can be unique on a cable network.
Downstream Frequency Override
Cisco uBR7200 series routers are able to change the downstream frequency for any or all cable modems,
overriding the DOCSIS configuration file settings.
CPE Limitation
Cisco uBR7200 series routers can report and limit the number of CPE devices per cable modem using
CLI commands or SNMP.
Note This feature is separate from the ability of a cable modem to support multiple CPE devices.
For example, depending on the Cisco IOS software release being used, Cisco uBR900
series cable access routers can support a maximum of either 3 or 254 CPE devices. Also,
by default, a DOCSIS-based cable modem supports one CPE device, but this can be
changed by modifying the MAX CPE parameter in the DOCSIS configuration file.
Burst Profile Configuration
For each modulation/burst profile configuration, Cisco uBR7200 series universal broadband routers will
support burst profile number, burst profile interval usage code, burst type, preamble length and unique
word length, differential encoding enable/disable, forward error correction (FEC) correctable bytes
value, FEC code word length, scrambler seed value, maximum burst size, guard time size, last code word
shortened/lengthened, and scrambler enable/disable.
Note Multiple burst profiles are supported on the MC11C, MC12C, MC14C, MC16B, and
MC16C cable modem cards. Only one profile is supported on the original MC11-FPGA
card.
Cable Modem and Host Subnet Addressing
The Cisco uBR7200 series cable access routers can manipulate the GIADDR field of DHCPDISCOVER
and DHCPREQUEST packets with a Relay IP address before they are forwarded to the DHCP server.
By modifying the GIADDR field based on whether the source is a cable modem or a host, the
Cisco uBR7200 series provides hints to the DHCP server as to where (that is, on which IP subnet) the
server should allocate addresses to the requesting client.
