Asynchronous Terminal Connections; Interference Considerations - Cisco ASR 903 Installation Manual

Preparing for Installation
The extent of your network and the distances between the network interface connections depend in part on
the following factors:
• Signal type
• Signal speed
• 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 in planning your network connections
prior to installing the Cisco ASR 903 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 RSP provides a console port to connect a terminal or computer for local console access through RJ45
connector or USB connector. The RJ45 port connector 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 can cause data errors or damage to the equipment.
The following sections describe sources of interference and how to minimize its effects on the Cisco ASR
903 Router system.
Electromagnetic Interference
All 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 Cisco ASR 903 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 903 Router,
see Regulatory Compliance and Safety Information for the Cisco ASR 903 Router.
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.
Cisco ASR 903 and ASR 903U Aggregation Services Router Hardware Installation Guide
Asynchronous Terminal Connections
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