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Ethernet Connector and Cabling
The coaxial cable used should be very high-quality cable because imperfections that do not visibly
affect video transmissions can significantly affect digital data transmissions. In particular, poor
insulation, improperly installed additional outlets, the condition and length of the cable's center
conductor, and the quality of the cable can negatively affect the connectivity and performance of the
cable voice adapter for digital data transmission.
For example, a 5 dB reduction in signal quality for analog downstream video might cause a slight
degradation of picture clarity, which might or might not be noticeable to a subscriber. However, a
reduction of only 1 dB in signal quality for digital data might completely disrupt service to a cable
network user.
Cisco recommends that you use a headend-grade coaxial cable or a quad-shield coaxial cable with a
minimum of 60% + 40% braid and double foil insulation to connect the cable modem cards to the HFC
network. The center conductor must be straight and extend 1/8 inch (3.2 mm) beyond the end of the
connector, and the connector should be securely crimped to the cable. The following cables are
recommended:
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•
•
All three of the coaxial cables listed can be used to connect a Cisco CVA122/CVA122E
Note
Cable Voice Adapter to the HFC network; however, the consistent use of RG-59 cable is
preferred.
If you use different types of coaxial cable, the following problems can appear:
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Ethernet Connector and Cabling
The Cisco CVA122/CVA122E Cable Voice Adapter has a single RJ-45 connector that provides the
following Ethernet 10BaseT connectivity:
•
•
Figure B-2 shows the RJ-45 connector and plug used for the cable voice adapter's Ethernet ports.
Table B-1 lists the pinouts and signals for the RJ-45 connector.
Cisco CVA122/CVA122E Hardware Installation Guide
B-2
RG-59—0.034 inch (0.86 mm) center conductor diameter
RG-59/U—0.0226 inch (0.57 mm) center conductor diameter
RG-6—0.041 inch (1.05 mm) center conductor diameter
Co-channel interference—If signals at the same frequency are carried on long, parallel runs of
coaxial cable, interference can occur between the signals. Higher quality cable helps to prevent this
with better shielding. Co-channel interference is seen as hum or patterns in analog video channels
and intermittent data loss in digital channels.
Damage to Cisco CVA122/CVA122E Cable Voice Adapter connector—The coaxial connectors are
designed for RG-59 or RG-6 cable and connectors. Larger cables can damage the connectors.
High signal return loss—High quality cable and correct connectors help to ensure an optimal return
loss of 16 dB or higher.
A single computer be connected directly to the cable voice adapter through the Ethernet port. Use
a straight-through cable for this connection.
When the cable voice adapter is configured for routing mode, its Ethernet port can be connected to
an Ethernet hub, which in turn can be connected to additional computers and other Ethernet
devices. Typically, a crossover cable connects the cable voice adapter's port to the 10BaseT
Ethernet port on the hub. (However, you may be able to use a straight-through cable if the hub has
an uplink port; see the hub's documentation for further details.)
Appendix B
Connector and Cable Specifications
OL-0799-02 (05/2001)
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Troubleshooting
