Accurate characterization and testing of installed optical fiber cabling is crucial to ensuring overall network integrity and performance.  Fiber type, link length, the number and quality of terminations and splices, cable stresses, and wavelength can all affect attenuation measurements.

TSB-140 “Additional Guidelines for Field-Testing Length, Loss and Polarity of  Optical Fiber Cabling Systems” was developed by the TIA TR-42.8 Telecommunications Optical Fiber Cabling Systems Subcommittee (which has since been merged with the TR-42.11 Optical Systems Subcommittee) and published in February, 2004.  TSB-140 provides descriptions for two Tiers of optical fiber test measurement methods and describes field-testing of length, optical attenuation and polarity in optical fiber cabling using an optical loss test set (OLTS), optical time domain reflectometer (OTDR) and a visible light source such as a visual fault locator (VFL).   Tier 1 testing entails testing installed optical fiber cabling for attenuation with an optical loss test set (OLTS) and verifying the cabling length and polarity.  Tier 2 testing, which is optional, includes the Tier 1 tests plus the addition of an optical time domain reflectometer (OTDR) trace.  An OTDR trace can be used to characterize the installed fiber link resulting in an indication of the uniformity of cable attenuation and connector insertion loss.

TSB-140 Content

  • Test Criteria
  • Test Instruments
  • Precautions to Measurement Testing
  • Documentation
  • Annexes addressing: Mandrel Wrap Usage for Multimode Fiber Testing with an OLTS LED Source and Interpreting Length, Attenuation Rate, and Insertion Loss from an OTDR Trace

TSB-140 Tier 1 and Tier 2 Optical Fiber Field Testing Tiers

  • Tier 1
    • Includes insertion loss with an OLTS
  • Tier 2
    • Adds OTDR testing to OLTS loss testing
    • Some objections to including OTDR testing includes:
      • Confusion as to which “tier“ is appropriate
      • OTDRs do not record loss as accurately as OLTS
      • Few premises cabling installers are adequately trained in interpreting OTDR data

TSB-140 Link Attenuation Considerations

Link attenuation can be negatively influenced by severe cable bends, poorly installed connectors or even the presence of dirt on the end face of connectors.  The attenuation measurement result should always be less than the designed attenuation budget (also known as loss budget) that is based on the number of terminations and cable length.  Documenting the test results provides the information that demonstrates the acceptability of the cabling system or support of specific networking technologies.

 

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