Cisco 7246 - uBR Router, Руководство по установке оборудования

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4-4
Cisco uBR7200 Series Universal Broadband Router Hardware Installation Guide
OL-5421-03
Chapter 4 Connecting the Cisco uBR7200 Series Router to the Cable Headend
Connecting and Configuring the Downstream
•
Noise funneling—The upstream data path to the headend is susceptible to picking up noise and
interference from anywhere in the network, and all upstream noise ultimately ends up at the
headend. This effect is known as
noise funneling because of the cumulative nature of the noise from
one or more locations in the network that becomes concentrated at the headend. As a network
serviced by a single upstream receiver increases in size, the probability of noise funneling also
increases.
• Variable transmit levels—Signal loss over coaxial cable is affected by temperature. This can cause
variations of 6 to 10 dB per year.
•
Clipping—The lasers in fiber-optic transmitters can stop transmitting light (clipping) when input
levels are excessive. Excessive input levels may cause bit errors and reduced data throughput in both
the upstream and downstream transmissions. If a laser is overdriven as briefly as a fraction of a
second, clipping can occur.
Connecting and Configuring the Downstream
After you install the Cisco uBR7200 series universal broadband router in your headend site, you must
connect the Cisco uBR7200 series to the HFC network and configure the network. The following
sections describe how to connect to and configure the downstream.
Installing and Configuring the Upconverter
If you have not already done so, unpack the IF-to-RF upconverter at your headend site and install it near
your Cisco uBR7200 series universal broadband router.
Note
Refer to the user documentation that accompanied your upconverter for safety information and specific
installation instructions.
Caution If you do not properly configure the upconverter, you might see decreased system performance,
increased packet loss, and a reduction in carrier-to-noise ratios.
Note
You might need to add attenuation to the downstream path between the Cisco uBR7200 series cable
interface line card and the upconverter. Cisco cable interface cards produce an IF output level of either
+32 dBmV (+/–2 dB), +40 dBmV (+/–2 dB), or +42 dBmV (+/–2 dB) depending upon which version
of cable interface card you have installed. Add enough attenuation to adjust the cable interface line card
IF output level to match the IF input level of your upconverter and to compensate for cable line loss, the
cable interface line card’s actual measured output power, and upconverter performance.
For more information refer to the Cisco uBR7200 Series Universal Broadband Router Cable Interface
Line Card Hardware Installation Guide at the following URL:
http://www.cisco.com/en/US/docs/interfaces_modules/cable/line_cards/installation/guide/mcxxfru.htm
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