user manual

Configuring Headend Broadband Access Router Features
Headend Broadband Access Router Configuration Prerequisites
MC-533
Cisco IOS Multiservice Applications Configuration Guide
data. The DOCSIS specification sets the minimum value for both of these parameters to 25 dB in the
5-MHz to 42-MHz frequency range. If the CNR drops below this value on a particular channel due to
noise, the cable modem on that channel will drop off of the HFC network.
We recommend that system administrators use upstream frequency hopping as a countermeasure to
long-term narrowband noise. To provide this capability, Cisco uBR7200 series routers contain a
spectrum manager that continuously monitors the noise in unused upstream channels. If the CNR reaches
an unacceptable level on a particular channel, the spectrum manager will automatically assign a new
upstream channel to the cable modem using that channel. This is referred to as frequency agility.
Cisco uBR7200 series routers support the following techniques for upstream frequency hopping when
no clean frequency band is available:
• Blind frequency hopping—The spectrum manager automatically assigns a new upstream channel
frequency when station maintenance (keepalive) messages fail for approximately 2.5 minutes. This
represents a complete impairment of the upstream due to noise, plant, or equipment failure.
• Time scheduled frequency hopping—Frequency reassignment is based on the time of day or week.
• Combined blind and time scheduled reassignment.
• Guided frequency hopping—Explicit frequency subbands and associated input power levels are
assigned in a spectrum group.
Note Frequency hopping is not effective against broadband noise phenomena such as impulse
noise.
The Cisco uBR7200 series allows you to create up to 32 cable spectrum groups, each containing multiple
upstream ports. The configured channel width is used for each upstream. In addition, the router
maintains a flap list containing the MAC address for each cable modem having problems maintaining its
connection. (A “flapping modem” is a cable modem that rapidly disconnects and reconnects to the
CMTS.)
Note Because spectrum management capabilities focus on the upstream path over an HFC
network, this feature is not applicable to one-way (telco return) systems.
Headend Broadband Access Router Configuration Prerequisites
Before you can configure Cisco uBR7200 series universal broadband router features, you must first
perform the following tasks:
• Make sure that your current network is designed to support broadband transmission. At the very
least, your network must include the following:
– Computer on the WAN side of your Cisco uBR7200 series configured as a DHCP server to
assign IP addresses to cable modems on the HFC network.
– Cisco uBR7200 series-compatible IF-to-RF upconverter installed in the downstream data path
at your headend site. The upconverter is installed between the Cisco uBR7200 series and the
combiner.
Note The combiner refers to all cables, amplifiers, and taps at the headend or cable distribution
center that connect the Cisco uBR7200 series to the HFC network.