4-3
Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
OL-17309-02
Chapter4 Connecting the Cisco uBR7225VXR Router to the Cable Headend
One-Way Data Headend Architecture
One-Way Data Headend Architecture
Figure 4-2 shows a typical headend configuration configured for one-way (downstream) data in a telco
return cable system.
Figure4-2 Typical Cable Headend Configuration for One-Way (Telco Return) Data
RF and Digital Data Overview
This section describes the interaction of digital and analog RF data as both signals are carried on the
hybrid fiber-coaxial (HFC) network.
Two-way digital data signals are more susceptible than one-way signals to stresses in the condition of
the HFC network. Degradation in video signal quality might not be noticed, but when two-way digital
signals share the network with video signals, digital signals might be hampered by the following types
of network impairments:
•Impulse and electrical noise—Impulse and electrical noise, usually forms of ingress, can enter the
network from sources within a home, such as hair dryers, light switches, and thermostats; or from
high-voltage lines that run near CATV cabling in the network. Areas of signal ingress may be located
and repaired by implementing a comprehensive signal leakage maintenance program.
•Amplifier thermal noise—Amplifiers add noise to the HFC network that usually goes unnoticed in
video signals, assuming a properly designed and operated network. Improperly configured
amplifiers will degrade digital data signals. The larger the network, the higher the probability of
amplifier thermal noise affecting the signals.
•Ingress noise—Ingress noise includes electrical sources (see “Impulse and electrical noise” above);
amateur radio transmissions; citizens band radios; or high-power shortwave broadcast signals,
which can interfere with frequencies anywhere between 3 and 65M Hz. These often are picked up
by cabling and equipment in the network.
Note Some HFC upstream equipment passes interfering signals below 5 MHz, which may overload the reverse
path.
DHCP
TFTP
TOD
servers
Cisco
uBR7225VXR
Downstream
RADIUS dial
security server
IP network access
Cisco network
access server
Telco return
cable modems
Upstream
Laser
transmitter
Broadcast
Narrowcast
0 to 20 dB
attenuator
(as required)
8-way
tap
3-way
splitter
+17 dBmV
video carrier
(typical)
+7 dBmV
data carrier
(typical)
Optical
splitter
Node 1
Node 2
Downstream
forward
test point
Main
headend feed
PSTN
271672