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Provisioning the Cable Headend
Headend Wiring
This section provides guidelines for setting up the headend wiring and cabling at your site. When
planning the location of the new system, consider the distance limitations for signaling, EMI, and
connector compatibility, as described in the following sections.
Interference Considerations
When wires are run for any significant distance in an electromagnetic field, interference can occur
between the field and the signals on the wires. This fact has two implications for the construction of
headend wiring:
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If you use twisted-pair cable in your headend wiring with a good distribution of grounding conductors,
the wiring is unlikely to emit radio interference. If you exceed the recommended distances, use a
high-quality twisted-pair cable with one ground conductor for each data signal when applicable.
If wires exceed recommended distances, or if wires pass between buildings, give special consideration
to the effect of a lightning strike in your vicinity. The electromagnetic pulse caused by lightning or other
high-energy phenomena can easily couple enough energy into unshielded conductors to destroy
electronic devices. If you have had EMI problems in the past, you might want to consult experts in
electrical surge suppression and shielding.
Distance Limitations and Interface Specifications
The size of your networks and the distances between connections depend on the type of signal, the signal
speed, and the transmission media (the type of cabling used to transmit the signals). For example,
standard coaxial cable has a greater channel capacity than twisted-pair cabling. The distance and rate
limits are the IEEE-recommended maximum speeds and distances for signaling; however, you can
usually get good results at speeds and distances far greater than these. For example, the recommended
maximum rate for V.35 is 2 Mbps, and it is commonly used at 4 Mbps without any problems. If you
understand the electrical problems that might arise and can compensate for them, you should get good
results with rates and distances greater than those recommended by IEEE; however, do so at your own
risk.
We recommend that you do not exceed specified transmission rate and distance limits.
Note
When preparing your site for network connections to the Cisco uBR7225VXR router, you must consider
a number of factors related to each type of interface:
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Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
2-14
Bad wiring practice can result in radio interference emanating from the wiring, ingress noise,
co-channel interference, and degraded or erratic universal broadband router performance.
Strong EMI, especially when caused by lightning or radio transmitters, can destroy the signal drivers
and receivers in the Cisco uBR7225VXR router, and can even create an electrical hazard by
conducting power surges through lines and into equipment. (Review the safety warnings in the
"Safety with Electricity" section on page
The type of cabling required for each type of interface (fiber, thick or thin coaxial, shielded
twisted-pair, or unshielded twisted-pair cabling)
Distance limitations for each signal type
The specific cables you need to connect each interface
Chapter 2
Preparing the Cisco uBR7225VXR Router for Installation
2-3.)
OL-17309-01
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