Dark Fiber Testing and Debugging Process

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Isolating Dark Fiber Service Issues

Dark Fiber is where ACD provides physical fiber cable connectivity between two or more sites. ACD generally does not operate or maintain the equipment for the customer.


Point of Demarcation and Responsibility

ACD Responsibility:

  1. Fiber Cable that is outside of the building
  2. Fiber Cable coming into the building; and is prior to the fiber termination box.
  3. The fiber termination box, and the connectors directly attached to the fiber termination box.

Customer Responsibility

  1. Patch cables from the fiber termination box to their equipment.
  2. Network Switches/Routers
  3. Optics; typically these are pluggable modules, such as GBICs, SFPs, Xenpaks and other industry names for Optical Modules.

Problem Reporting by Customer

When a customer reports an issue with dark fiber we need to know the nature of the problem reported:

  1. Outage: Where there is no connectivity between sites.
    1. Is the outage affecting all fibers between a site or only specific fibers?
    2. Need to know which fibers?
  2. Transmission Errors Transmission occuring, but CRC errors on equipment.
    1. Is this occuring on all fibers between a site or only specific fibers?
    2. Are the errors on both on the TX and RX sides of the circuit?
  3. Intermittent Trasmission Errors Transmission is occuring, but CRC errors on equipment is intermittent
    1. How often are the CRC errors occuring, i.e. is there a pattern or cycle to the errors?
    2. What time of day? Any pattern?
  4. Low Light Level The light emitted from the customer's laser is low on the RX end?
    1. What is the DB attenuation of the fiber strand that is having a problem?
    2. What is the loss ratio from the Launch Laser to the Terminating location?
    3. Is this occurring on all fiber strands?

Impact of ACD testing

In order to test dark fiber strands that are having issues, the customer equipment needs to be disconnected. There is no way to test fibers without disconnecting equipment, therefore any request should be with the understanding that it will be service affecting, and should be put in either a maintenance window or in the event of a complete outage.

If there are spare adjacent fibers that are on the same cable, we can test these for continuity of the overall fiber cable. If the spare cables are functional, equipment can be reloacted to the spare cable.

Equipment and Documentation Required for Testing

  1. 1 Light Meter: A light meter is a devices that is able to read the light strength from the emitting laser. The light meter tells whether the laser light being emitted is strong or weak, and within the range of the light sensor to read the light.
  2. 2 OTDR Meter: A Optical Time Domain Reflectometer (OTDR) is an expensive device that sends a series of signals down a fiber strand to determine a number of aspects about the fiber cable. A OTDR device can tell where a) A bad splice exists b) Potentially where there is damage that is decreasing the strength of the light signal, c) determine the length of the fiber strand. This is most relevant if the length is less than the actual length of a cable, this means that there is a break in the cable somewhere.
  3. 3 OTDR Documentation: OTDR documentation is the documents that are created at the time of delivery of the fiber service to the customer. This documentation lists the characteristics of each individual fiber strand, just after it was built. By comparing the historical OTDR readings to the current OTDR reading it can be determined if there is now a difference in the cable

As-Built Drawings

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