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Service Guides: Dark Fiber Service (DFS)
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2. DFS Technical Description

DFS Technical Summary

A fiber cable typically contains many optical fibers, which are either "lit" to carry a signal or "unlit" to be used at a future date. A Dark Fiber is an optical fiber through which no light is transmitted. The simplest Dark Fiber Service is a point-to-point connection between two locations. More elaborate configurations (e.g. Diverse Ring, Star, etc.) enable Agencies to interconnect any number of selected locations. DFS is a new service that was not offered on FTS2001 contracts.

DFS is acquired as a facility which will allow the Agency the indefeasible right of use of the fiber route. The term fiber route could mean a fiber pair in a fiber-optic cable, or the entire fiber-optic cable.

DFS may be ordered for inter-city, intra-city interconnections in the CONUS and OCONUS with Non-Domestic locations being optionally offered. The Agencies have the option either to provide their own optoelectronics equipment or to obtain optoelectronics equipment from the contractor. DFS is delivered to the customer-specified Service Delivery Point (SDP). The Agency can order DFS that will connect to and interoperate with:

  • Contractor's metro and long haul networks
  • Internet
  • Agency's network
  • Other Agency networks in the same vicinity

The diagram below illustrates a CONUS wide contractor's DFS transport network delivering available optical paths to the Agency between two cities. Collocation capabilities are available from the contractor to host Agencies' optoelectronics if required. Collocation capabilities include the capability to add/drop traffic (gateways) and to regenerate and amplify traffic where needed.



3. DFS Technical Detail

The SDP for DFS is where the Agency has installed its optoelectronics. The Agency determines the specific location of the Service Delivery Point (SDP) for the contracted DFS route(s). The SDP can be either a fiber patch panel at a Government location or a collocation facility.

The contractor will provide optical fiber strands as specified by the Agency that complies with the optical performance characteristics (KPIs) as in Section C.2.5.3.1.4. of the Networx contracts. Fiber types include NZDS (Non-Zero Dispersion Shifted), LEAF, True-Wave, and SMF-28 for distances less than 60 km). The fiber installed will have to work with the specified amplifier types as required by the Agency (i.e., Erbium- doped Fiber Amplifiers (EDFA), Raman Amplifiers, EDFA/Raman hybrid Amplifiers, Semiconductor Optical Amplifiers (SOA)). The Agency also determines the number of fiber strands to be supported and the number of ducts required between the connecting locations.

The Agency can specify its expected growth to allow the contractor to plan infrastructure build-up based on such forecast. The Agency is also able to specify if gateways (add/drop points in the network) will be needed and their locations.

DFS features that may be ordered include:

  • Collocation Services for hosting Agency optronics
  • Diverse Routes Single and Multi Drops to prevent service interruptions
  • Multiple Ducts for fiber installation
  • Off-Net Laterals (fiber cables from the Agency's premises to the nearest splice point on the DFS cable trunk)

A complete description of DFS features can be found in Section C.2.5.3.2.1 (Dark Fiber Features) of the Networx contract.

Each Networx contractor may provide variations or alternatives to the offering and pricing for DFS. The specific details can be found within each Contractor's Networx contract files and pricing notes for DFS.

For more information on the general DFS specifications and requirements, please refer to Section C.2.5.3 of the Networx contract for technical specifications and Section B.2.5.3 for pricing.

4. DFS Price Description

DFS Price Basics

Dark Fiber is an optical fiber through which no light is transmitted and can be later "lit" and used to carry an optical signal. DFS capacity may be purchased in single fiber strand(s) or pair(s) within a fiber-optic cable. Charges for the actual fiber or to light the fiber are not included in DFS. DFS is a service that was not offered on the FTS2001 contracts.

The MRC for transport consists of a fixed component plus a distance-dependent (per mile) component. CONUS-to-CONUS distance is calculated using the distance formula:

  • Distance (miles) = ROUNDUP(SQRT(((V1-V2)^2+(H1-H2)^2)/10),0) Where (V1, H1) and (V2, H2) are the V and H coordinates of the locations, respectively

Distance involving OCONUS or non-domestic locations is calculated using airline miles. Note: The Networx Pricer automatically calculates the distance when given the originating and terminating locations.

Price components required for full end-to-end service for Domestic and Non-Domestic DFS:

  • DFS Transport monthly recurring charge with a fixed component and charge per mile for the Indefeasible Rights of Use (IRU) per pair of fibers or per fiber, for on-net connections or along routes where fiber is installed. The management, ongoing monitoring support, maintenance, and repair of DFS due to normal wear and tear and repairing of DFS in case of breaks are included in the MRC.
  • DAA Originating and Terminating Wireline Access (MRC) and (NRC)
      The following features may be ordered as needed by the Agency:
    • Collocation Service
    • Duct
    • Dark Fiber Local Loop
    • Diverse Route Single Drop
    • Diverse Route Dual Drop
    • Inter-city Connectivity
    • Multiple Duct
    • Off-net Laterals
  • Service Enabling Devices (SEDs) may be required to implement DFS. [Please note that SEDs under Networx replace the FTS2001 User-to-Network Interfaces and Access Adaptation Functions (UNIs/AAFs). SEDs may differ between Networx providers. The pricing structure for SEDs provides for either a one-time payment or monthly term payments for purchase, plus a NRC for installation, and a MRC for maintenance.]

Example: One DFS Fiber Pair



  • DFS Transport: Choose CLIN 160106 (DFS - Fiber Pair - Less than 12 Fiber Pairs)
  • Access NRC: Choose CLIN 760174 Routine DAA DFS Fiber Pair NRC (ICB) for both ends of the transport. Prices for this CLIN are not available in the unit pricer. Prices are available on an Individual Case Basis (ICB).
  • Access MRC: Choose CLIN 760374 Routine DAA DFS Fiber Pair MRC (ICB) for both ends of the fiber. Prices for this CLIN are not available in the unit pricer. Prices are provided by the contractor after a street address has been provided and a case number has been assigned.
  • SEDs must be chosen based on equipment required at each location. CLINs may differ between contractors.

Each Networx contractor may provide variations or alternatives to the offering and pricing for DFS. The specific details can be found within each Contractor's Networx contract files and pricing notes for DFS.

For more information on the general DFS specifications and requirements, please refer to Section C.2.5.3 of the Networx contract for technical specifications and Section B.2.5.3 for pricing.