Cisco VG224 Hardware Installation Guide - Page 31

Chapter 2 Planning Your Installation Distance Limitations for Interface Cables Cable Types The cable types that are used are dependent on the Cisco VG224 voice gateway that you are using. For more information, see the "Interfaces and Service Capabilities" section on page 1-4 and Appendix A, "Cable Specifications and Information." • Fast Ethernet cables (RJ-45-to-RJ-45 straight-through cables) • Analog voice cables (RJ-21) 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: • Fast Ethernet Maximum Distance, page 2-5 • FXS Analog Voice Port Maximum Distance, page 2-5 Fast Ethernet Maximum Distance The maximum segment distance for Fast 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. 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 VG224 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 centers cannot resolve the 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. OL-5006-04 Cisco VG224 Voice Gateway Hardware Installation Guide 2-5