user manual

Configuring Headend Broadband Access Router Features
Configuring and Activating Frequency Agility
MC-565
Cisco IOS Multiservice Applications Configuration Guide
Figure 109 Sparse Versus Dense Segment Illustrations
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.
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