Specifications

3-12

Cisco Cable Modem Termination System Feature Guide

0L-1467-02

Chapter 3 Spectrum Management for the Cisco Cable Modem Termination System

Feature Overview

Time-Scheduled Frequency Hopping

You can specify upstream channel frequency reassignment based on a configured time of every day or

of a specific day of the week. If your cable plant has an upstream noise characteristic on a weekly cycle,

use time-scheduled spectrum allocation. With a time-scheduled policy, a single frequency becomes valid

at any given time.

Dynamic Upstream Modulation (SNR-based)

The Dynamic Upstream Modulation feature is supported on the Cisco uBR-MC1xC and

Cisco uBR-MC16S cable interface line cards beginning with Cisco IOS Release 12.1(3a)EC1,

Cisco IOS Release 12.2(4)BC1b, and later releases.

The Dynamic Upstream Modulation feature operates differently on the Cisco uBR-MC16S cable

interface line card than on other supported cable interface line cards. See the description of this feature

in the “Advanced Hardware-Based Spectrum Management” section on page 3-14 for more information.

Cisco uBR-MC1xC (and Cisco uBR-MC16S) cable interface line cards monitor SNR and forward error

correction (FEC) counters in the active return path of each upstream port. The Dynamic Upstream

Modulation software determines whether upstream channel signal quality can support the modulation

scheme configured, and adjusts to the most robust modulation scheme when necessary. When return path

conditions improve, this feature returns the upstream channel to the higher modulation scheme that

includes the modulation profile.

A modulation profile is a collection of six burst profiles that are sent out in a UCD message to configure

modem transmit parameters for the upstream message types: request, request/data, initial maintenance,

station maintenance, short grant, and long grant. Dynamic Upstream Modulation adjusts the modulation

profiles of an upstream channel based on upstream signal quality.

Dynamic Upstream Modulation can be configured on interfaces with fixed upstream frequencies or on

interfaces with assigned spectrum groups.

For a Cisco uBR-MC16C cable interface line card only, the QAM-16 channel can change automatically

to a QPSK channel, based on the SNR estimate of the receiver circuitry and FEC

correctable/uncorrectable thresholds of a particular upstream channel.

For information on commands to configure Dynamic Upstream Modulation, see “Configuring Dynamic

Upstream Modulation” section on page 3-32.

Note The automatic switch of a QAM-16 to QPSK feature is available only on Cisco uBR-MC16C and

Cisco uBR-MC16S cable interface line cards.

For example, if you configure Dynamic Upstream Modulation on the Cisco CMTS using modulation

profiles 1 and 2, where:

• Modulation profile 1 is the primary modulation profile using QAM-16

Modulation profile 1 (QAM-16) uses the more bandwidth-efficient modulation scheme and has a

higher throughput than modulation profile 2 (QPSK).

• Modulation profile 2 is the secondary modulation profile using QPSK

Modulation profile 2 (QPSK) uses the more robust modulation scheme, but it is not

bandwidth-efficient.

Note Cisco recommends that the primary proﬁle uses QAM-16 modulation and the secondary uses QPSK, but this

is optional. The two modulation proﬁles can both be QPSK or QAM-16. It is not mandatory that one is

QAM-16 and the other QPSK, but modulation proﬁle switchover is tied to QAM-16 and QPSK thresholds.