Specifications

3-2
Cisco Cable Modem Termination System Feature Guide
0L-1467-02
Chapter 3 Spectrum Management for the Cisco Cable Modem Termination System
Feature Overview
Feature Overview
Spectrum management is a software and hardware feature provided in the Cisco Cable Modem
Termination System (CMTS) so that the CMTS may sense both downstream and upstream plant
impairments, report them to a management entity, and automatically mitigate them where possible. The
CMTS directly senses upstream transmission errors. It may also indirectly monitor the condition of the
plant by keeping a record of modem state changes. The spectrum management feature performs these
functions without reducing throughput or latency and without creating additional packet overhead on the
radio frequency (RF) plant.
The purpose of spectrum management is to prevent long-term service interruptions caused by upstream
noise events in the cable plant. It is also used for fault management and troubleshooting the cable
network. When cable modems are detected to go online and offline by flap detectors, the cable operators
can look at the flap list and spectrum tables to determine the possible causes.
Due to the nature of cable television (CATV) technology, upstream noise management is a significant
issue. Frequency bands must have a sufficient carrier-to-noise ratio (CNR) and carrier-to-ingress power
ratio to support the transmission of quadrature phase-shift keying (QPSK) and quadrature amplitude
modulation (QAM) data. The Data-over-Cable Service Interface Specifications (DOCSIS) set the
minimum value for both of these ratios to 25 dB in the 5-MHz to 42-MHz frequency range. If the CNR
drops below 25 dB on a particular channel due to noise, the cable modem on that channel degrades and
can drop off the hybrid fiber-coaxial (HFC) network.
This overview contains the following subsections:
Subsection Description
Upstream Signal Channel Overview, page 3-3 Describes how signals are sent and how changes occur
in upstream channels.
Upstream Segments and Combiner Groups,
page 3-4
Describes sparse and dense segments and combiner
groups.
Frequency Management Policy, page 3-5 Describes the types of noise impairments and how to
counteract ingress noise with spectrum groups and
frequency hopping.
Phases of Spectrum Management, page 3-6 Describes the three phases of spectrum management
and the Cisco IOS releases in which support started.
Guided and Scheduled Spectrum
Management, page 3-7
Describes the following Guided and Scheduled
spectrum management features: traffic shaping,
frequency hopping capabilities, dynamic upstream
modulation (SNR-based), and input power levels.
Advanced Hardware-Based Spectrum
Management, page 3-14
Describes spectrum management features that are
supported by the Cisco uBR-MC16S and
Cisco uBR-LCP2-MC16S cable interface line cards:
• Intelligent spectrum management capabilities that
include a spectrum analyzer for more intelligent
and faster frequency hopping
• Advanced spectrum management features that
include CNR-based, proactive frequency hopping
and a more robust dynamic upstream modulation