• GE cables
• Analog voice cables (RJ-11)
Distance Limitations for Interface Cables
When planning your installation, consider distance limitations and potential electromagnetic interference
(EMI) as defined by the Electronic Industries Association (EIA). Distance limitation information is included
for the following VG ports:
• Gigabit Ethernet Maximum Distance: The maximum segment distance for Gigabit Ethernet is 330 feet
(100 meters) (specified in IEEE 802.3).
• FXS Analog Voice Port Maximum Distance: The maximum distance is established by a total allowable
loop resistance, including the phone or terminal equipment, of 600 ohms.
• FXS-E (Extended loop) Analog Voice Port Maximum Distance: The maximum distance is established
by a total allowable loop resistance, including the phone or terminal equipment, of 1400 ohms.
Typically, a 26 AWG wire is equal to 81.6 ohm/Kft and 24 AWG wire is equal to 51.3 ohm/Kft.
Note
Interference Considerations
When you run cables for any significant distance in an electromagnetic field, interference can occur between
the electromagnetic field and the signals on the cables. This has two implications for the installation of terminal
plant cabling:
• Unshielded plant cabling can emit radio interference.
• Strong electromagnetic interference (EMI), especially as caused by lightning or radio transmitters, can
destroy the EIA/TIA-232 drivers and receivers in the Cisco vg400 Voice Gateway.
If you use twisted-pair cables with a good distribution of grounding conductors in your plant cabling, emitted
radio interference is unlikely.
If you have cables exceeding recommended distances, or if you have cables that pass between buildings, give
special consideration to the effect of lightning strikes or ground loops. If your site has these characteristics,
consult experts in lightning suppression and shielding. The electromagnetic pulse caused by lightning or other
high-energy phenomena can easily couple enough energy into unshielded conductors to destroy electronic
devices.
Most data centres cannot resolve such infrequent, but potentially catastrophic problems just described without
pulse meters and other special equipment. Take precautions to avoid these problems by providing a properly
grounded and shielded environment and by installing electrical surge suppression.
If you remove any module, you must either install a module in its place or install a cover plate over the opening.
All module openings must be either occupied or covered to prevent electromagnetic interference.
For advice on the prevention of electromagnetic interference, consult experts in radio-frequency interference
(RFI).
Cisco VG400 Voice Gateway Hardware Installation Guide
14
Planning Your Installation
Interference Considerations
