Sunday, June 11, 2017

Fiber Troubleshooting

CompTIA Network N10-006 Quick Reference

Fiber optics provide an advantage over copper cabling for Ethernet in that fiber-optic cables can go farther and have a higher capacity for throughput. They are not subject to radio frequency or electromagnetic interference because they don’t use copper for cabling but instead use light signals for transmitting and receiving data. Most of the problems presented in this chapter can be avoided or resolved by simply following the standards.
Attenuation/Decibel Loss—If a cable is longer than the specification or technology for which it is being used, the natural attenuation and decibel loss of the signal can cause the network to have faults or be completely unusable. The correction is to apply repeaters or other methods of regenerating signals so that the signal transmission is performed within the specifications of the technology being used.
SFP (Small Form-Factor Pluggable)/GBIC (Gigabit Interface Converter)—When fiber optics are used, switches can have a generic port that supports a module such as an SFP or GBIC module or adapter. The adapter chosen should be the correct one for the type of fiber termination as well as the type of fiber cable that is in use. If the incorrect SFP module for the incorrect cable type or termination is used, it could result in a failure. The resolution is to verify the type of module required, as well as the type of fiber cable that should be in place—for example, multimode versus single mode. Also within these categories are additional specifications that should be checked and verified.
Bad SFP/GBIC—The SFP or GBIC module acts as a transmitter and receiver that the switch uses to communicate over the fiber or Ethernet cable. If this adapter is the incorrect type, it would cause a failure of the fiber connection. Using the vendor’s show commands can reveal additional details regarding the module, including any failures that the module might be experiencing.
Wavelength Mismatch—The SFP, connectors, and cabling all must support the type of frequencies used over a fiber cable. If there is a mismatch among the module type, the cabling, and the termination is used, that could cause a failure. You should verify the vendor’s specifications and then confirm that the correct cable type and module are being used.
Fiber Type Mismatch—There are several types of fiber cabling, including multimode and single mode, and many variants within each of those categories. Confirm the use of the correct type of fiber cabling by comparing the standards along with the vendor’s requirements to make sure that the correct cabling is being used, as well as ensuring compatibility with the SFP, cable termination, and port.
Dirty Connectors—A dirty connector at the termination of the fiber-optic cabling could prevent the signals from being received or sent successfully over the fiber-optic cable. The fiber-optic cable itself might be the problem. Verify this by using a fiber-optic cable tester, and have the termination cleaned if found to be dirty. The SFP adapter could be swapped out as part of a troubleshooting process and then the fiber cable could be reconnected to correct the problem.
Connector Mismatch—SFP modules are designed for specific fiber-optic termination, as well as specific frequency types to be used over the fiber cabling. Certain types of cabling are designed for different types of connectors. If not all of these items are compatible, it could cause a failure of the fiber optics. The resolution is to check all the specifications and correct any components that are incompatible with the type of cabling or the technology being used.
Bend Radius Limitations—Fiber-optic cabling can be bent, to the extent that is planned for and documented as part of the specification (or recommendation) for that cabling. If the cable is bent in excess of the bend radius standards for fiber-optic cabling, the optical signal might not perform as well. There is also the potential for permanent damage to the fiber due to causing miniature cracks in the cable. To help mitigate the potential of cables being harmed, cable management including the use of cable trays should be used. They can help keep the cables organized and protected against excessive bending.
Distance Limitations—Going beyond the distance of a standard, whether it be wireless, copper-based wire, or fiber-optic cabling, puts the network at risk. Failures are more likely to occur. Cable testers, including those specific for fiber optics, can be used to verify cabling plants including the distance of a fiber-optic cable. If a cable is found to extend farther than is supported by the technology, it should be modified or replaced within specs.