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Figure 6: Typical Broadband Cable Network

A two-way, bidirectional network supports transmission

to and from the headend over HFC in both directions. In

the downstream direction, digital data is modulated and

placed on a TV carrier. Supported modulation schemes

include Quadrature Phase Shift Keying (QPSK) and

QuadratureAmplitudeModulation (QAM).ForDOCSIS

North American channel plans, this means a 6 MHz

channelbetween52 to860MHz.For EuroDOCSISPhase

AlternatingLine(PAL)andSystemeElectroniqueCouleur

Avec Memoire (SECAM) channel plans, this means an

8 MHz channel between 85 and 860 MHz. The digital

data signal is placed in a 6 or 8 MHz channel adjacent to

TV signals based on the Cisco uBR7100 Series Universal

Broadband Router purchased.

The upstream direction is trickier. In a two-way cable

architecture, the upstream tends to be noisy with

interference from home appliances, loose connectors, or

poor cabling. All noise travels upstream, combining and

increasing.

The Cisco uBR7100 Series gives you the choice of

modulation schemes. The importance of the data,

combined with cable characteristics, determine the

modulation scheme to use to ensure reliable transfer.

QPSK is more robust and provides a higher order

modulation technique, but is slower than QAM.

The Cisco uBR7100 Series Universal Broadband Router

supports transmission over cable networks that are not

yet two-way capable. Figure 7, that follows, depicts a

sample DOCSIS conﬁguration.

Upstream connections are over standard telephone lines.

The Cisco uBR7100 Series provides downstream data

from the cable line card and accepts upstream trafﬁc via a

combination of the local Public Switched Telephone

Network (PSTN) andtheIPnetworkpaththatterminates

at the router. Upstream data is through a telco-return

modem (external or internal to a cable modem based on

the third-party vendor).

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Cisco uBR7100 Series Bedienungsanleitung Seite 9