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Asynchronous Terminal Connections
• Transmission medium
The distance and rate limits referenced in the following sections are the IEEE-recommended maximum speeds
and distances for signaling purposes. Use this information as a guideline when planning your network
connections >prior to installing the router.
If wires exceed the 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 problems of this sort in the past, you may want to consult experts in electrical surge
suppression and shielding.
Asynchronous Terminal Connections
The router provides a console port to connect a terminal or computer for local console access. The router
supports RS-232 asynchronous data with distance recommendations specified in the IEEE RS-232 standard.
Interference Considerations
When wires are run for any significant distance, there is a risk that stray signals will be induced on the wires
as interference. If interference signals are strong, they may cause data errors or damage to the equipment.
The following sections describe the sources of interference and how to minimize their effects on the router
system.
Electromagnetic Interference
All the equipment powered by AC current can propagate electrical energy that can cause EMI and possibly
affect the operation of other equipment. The typical sources of EMI are equipment power cords and power
service cables from electric utility companies.
Strong EMI can destroy the signal drivers and receivers in the router and even create an electrical hazard by
causing power surges through the power lines into installed equipment. These problems are rare, but could
be catastrophic.
To resolve these problems, you need specialized knowledge and equipment that could consume substantial
time and money. However, you can ensure that you have a properly grounded and shielded electrical
environment, paying special attention to the need for electrical surge suppression.
For information about the electrode magnetic compliance standards supported on the Cisco ASR 920-10SZ-PD
and Cisco ASR-920-8S4Z-PD Routers, see the Regulatory Compliance and Safety Information for the Cisco
ASR 920 Series Aggregation Services Router document.
Radio Frequency Interference
When electromagnetic fields act over a long distance, radio frequency interference (RFI) may be propagated.
Building wiring can often act as an antenna, receiving the RFI signals and creating more EMI on the wiring.
If you use twisted-pair cable in your plant wiring with a good distribution of grounding conductors, the plant
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.
Lightning and AC Power Fault Interference
If signal wires exceed the recommended cabling distances, or if signal wires pass between buildings, you
should consider the effect that a lightning strike in your vicinity might have on the router.
Cisco ASR 920-10SZ-PD and Cisco ASR-920-8S4Z-PD Aggregation Services Router Hardware Installation Guide
24
Preparing for Installation
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