Cisco MC16S Bedienungsanleitung PDF herunterladen (Seite 4)

Spectrum Management Overview

12.0(7)XR2

Frequency Management Policy

Due to the nature of CATV technology, upstream noise management is a signiﬁcant issue. Cisco

recommends that you follow rigorous North American plant maintenance procedures documented

in the NCTA Supplement on Upstream Transport Issues to adjust return ampliﬁers and lasers.

Cisco also recommends that system administrators conﬁgure upstream frequency hopping as a

countermeasure to long-term, narrowband noise. Cisco IOS Release 12.0(5)T1 or higher CMTS

images support blind, time-scheduled, and guided frequency hopping.

With the release of the Cisco MC16S cable modem card, you can perform automatic upstream

frequency hopping. You can conﬁgure the MC16S to scan the upstream spectrum in your cable

network and point to “clean” available upstream channels (of a width you designate) to accept a

frequency hop.

Note The choice of spectrum is usually limited to those bands having sufﬁcient C/N ratio and

carrier-to-ingress power ratio to support transmission of QPSK and QAM data. The MC16S card

operates with default FEC values at approximately 15 dB SNR for QPSK, and 25 dB SNR for

16QAM. Bands with known ingress should be avoided.

Higher frequency bands are also preferred because they are least likely to suffer noise interference.

Measurement of noise power levels with a spectrum analyzer is a mandatory part of the setup

procedure to characterize your cable plant.

Upstream port frequency should be set to a ﬁxed value during system installation and testing. This

is chosen from the allocation plan for the RF domain for the RF plant segment connected to the

upstream.

Note Having ﬁxed frequency settings is recommended during early deployment at least until

ampliﬁer cascade adjustments or plant repair becomes infrequent for the nodes connected to the

upstream port. When multiple upstream ports are combined together to provide increased

bandwidth, care should be taken to prevent overlapping frequency bands.

When the system has reached sufﬁcient stability, the RF domain topology can be entered into the

Cisco IOS conﬁguration ﬁle to enable RF spectrum management. This management feature—called

spectrum groups described earlier—applies a common frequency management policy to a set of

upstream ports.

Note When each upstream port has its own RF domain, the group is called a non-shared spectrum

group. When multiple upstream ports share the same RF domain, the group is called a shared

spectrum group.

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