Cisco Systems uBR7200 manual Combiner Groups, MC-565

Configuring Headend Broadband Access Router Features

Configuring and Activating Frequency Agility

Figure 109 Sparse Versus Dense Segment Illustrations

Sparse

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Dense Segment 1

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1x4 CM card

DS

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27979

		Optical	Reverse optical
Segment		receiver	Fiber-optic transmitter
x	= attenuator	x attenuator	cable

Cable modems

Distribution

network

As shown in Figure 109, the downstream segment can contain multiple upstream segments. Two fiber nodes can be in one downstream segment but in different upstream segments.

An upstream frequency has an associated upstream input power level in dBmV. Cable operators must make noise measurements and determine the cable plant spectrum management policy. Different modulation schemes and symbol rates can be used based on the characteristics of the cable plant and the cable modem card contained in the Cisco uBR7200 series chassis. Bits are encoded into a two-dimensional mapping called a constellation. A good carrier-to-noise ratio is needed to properly decode symbols into bits.

Combiner Groups

The return path of several fiber nodes can be combined at a single point to form a single RF frequency domain called a combiner group. The Cisco uBR7200 series software allows a frequency hop table called a spectrum group to be associated with a combiner group.

Note A combiner group refers to an RF topology point. A spectrum group refers to the frequency hop table associated with a combiner group.

The Cisco uBR7200 series routers support up to 32 spectrum groups. Each spectrum group defines the table of frequencies to be used in a specific frequency plan. Cisco cable modem cards interface the downstream and upstream ports to the cable plant, while port adapters connect to the IP backbone and external networks.

Cisco IOS Multiservice Applications Configuration Guide

MC-565