Cisco Systems UBR7225VXR One-Way Data Headend Architecture, RF and Digital Data Overview

Chapter 4 Connecting the Cisco uBR7225VXR Router to the Cable Headend

One-Way Data Headend Architecture

One-Way Data Headend Architecture

Figure 4-2shows a typical headend configuration configured for one-way (downstream) data in a telco return cable system.

Figure 4-2

Typical Cable Headend Configuration for One-Way (Telco Return) Data

DHCP TFTP TOD servers

Cisco

uBR7225VXR

Downstream

Main

headend feed

Broadcast

	8-way		Narrowcast
0 to 20 dB		tap
				3-way
attenuator
				splitter
(as required)

Laser

transmitter

+17 dBmV

video carrier

(typical)

+7 dBmV

data carrier

(typical)

Node 1

Optical

splitter

Node 2

Downstream forward test point

IP network access		Telco return
	Cisco network	cable modems
RADIUS dial
	access server
security server
Upstream		PSTN
		271672

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 65 MHz. 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.

Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide

OL-17309-02 4-3