Cisco Systems UBR7225VXR specifications Headend Wiring, Interference Considerations

Chapter 2 Preparing the Cisco uBR7225VXR Router for Installation

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:

•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 2-3.)

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.

Note We recommend that you do not exceed specified transmission rate and distance limits.

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:

•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

	Cisco uBR7225VXR Universal Broadband Router Hardware Installation Guide
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