Dark fiber
From Wikipedia, the free encyclopedia
 |
The examples and perspective in this article or section may not represent a worldwide view of the subject. Please improve this article or discuss the issue on the talk page. |
In fibre-optic communications, dark fibre or unlit fibre (or fiber) is the name given to individual fibers that have yet to be used within cables that have been already laid. They are hence not yet connected to any device, and are only there for future usage.
The term was originally used when talking about the potential network capacity of telecommunication infrastructure, but now also refers to increasingly common practice of leasing fiber optic cables from a network service provider.
Contents |
[edit] Dark fibre for capacity expansion
One reason that dark fibre exists in well-planned networks is that much of the cost of installing cables is in so-called civils - the civil engineering work required in order to get the cables installed. This includes planning and routing, obtaining permissions, creating ducts and channels for the cables, and finally installation and connection. This work accounts for more than 60% of the cost of developing fiber networks, with only a relatively small proportion actually being invested in the optical fiber cable and high-tech networking infrastructure.[citation needed]
It therefore makes sense to plan for and install significantly more fibre than is needed for current demand, to provide for future expansion and provide for network redundancy in case any of the cables fail.
Additionally, many fibre optic cable owners such as railroads or power utilities have always added additional fibres for lease to other carriers.
In common vernacular, dark fibre may sometimes still be called "dark" if it's been lit by a fibre lessee and not the cable's owner.
[edit] Dark fibre overcapacity
In the dot-com bubble, a large number of telephone companies (or telcos) built optical fibre networks, each with the business plan of cornering the market in telecommunications by providing a network with sufficient capacity to take all existing and forecast traffic for the entire region served. This was based on the assumption that telecoms traffic, particularly data traffic, would continue to grow exponentially for the foreseeable future.
Unfortunately for them, the collapse of the dot-com boom left fiber supply greatly exceeding demand of even the most optimistic forecasts by a factor of up to 30 in many areas[citation needed]. The availability of wavelength-division multiplexing further reduced the demand for fibre by increasing the capacity that could be placed on a single fibre by as much as a factor of 100. As a result, the wholesale price of data traffic collapsed. A number of these companies filed for bankruptcy protection, or went bankrupt, as a result.
Just as with the Railway Mania, the misfortune of one market sector became the good fortune of another, and this overcapacity created a new telecommunications market sector.
At any given time, about 97% of fibre optic cable in the US is dark.[citation needed]
[edit] The dark fibre market
For many years, incumbent local exchange carriers would not sell dark fibre to end users, because they believed selling access to this core asset would cannibalize their other, more lucrative services. Incumbent carriers in the US were required to sell dark fiber to competitive local exchange carriers as Unbundled Network Elements (UNE), but they have successfully lobbied to reduce these provisions for existing fiber, and eliminated it completely for new fiber placed for fiber to the premises (FTTP) deployments.
Competitive local carriers were not required to sell dark fibre, and many do not, although fiber swaps between competitive carriers are quite common. This increases the reach of their networks in places where their competitor has a presence, in exchange for provision of fiber capacity on places where that competitor has no presence. This is a practice known in the industry as "coopetition".
Meanwhile, other companies arose specializing as dark fibre providers. Dark fiber became more available when there was enormous overcapacity after the boom years of the late 1990's through 2001. The market for dark fibre tightened up with the return of capital investment to light up existing fiber, and with mergers and acquisitions resulting in consolidation of dark fiber providers.
In the U.S. Level(3) Communications acquired a number of dark fiber providers in 2005-2006, and took their dark fibre off the market. In December 2006, AboveNet quietly removed its Access-darkfiber product from its web site with no public announcement. There is a market segmentation between dark fiber providers and lit service providers, although in some cases both models were used by the same entities. Currently there are no major national carriers still offering dark fiber, and all dark fiber providers are regional network operators.
Dark fibre has been, and still is, available for sale on the wholesale market for both metro and wide area links, but it may not be available in all markets or city pairs. Prices for dark fibre may sometimes be lower than the price of a high speed leased line rental.
Dark fiber capacity is typically used by network operators to build SONET and dense wavelength division multiplexing (DWDM) networks, usually involving meshes of self-healing rings. Now, it is also used by end-user enterprises to expand Ethernet local area networks, especially since the adoption of IEEE standards for Gigabit Ethernet and 10 gigabit Ethernet over single-mode fiber. Running Ethernet networks between geographically separated buildings is a practice known as "WAN elimination".
[edit] Other variations
- Managed dark fiber is a form of wavelength-division multiplexed access to otherwise dark fiber where a simple "pilot" signal is beamed into the fiber by the fiber provider for management purposes using a transponder tuned to the assigned wavelength. DWDM systems generally require central management because their closely spaced wavelengths are subject to disruption by signals on adjacent wavelengths that are not within tightly controlled parameters, especially if amplification is required for signal transmission over more than 100 km or so.
- Virtual dark fiber using wavelength multiplexing allows a service provider to offer individual wavelengths ("lambdas" (λ) or "colors"), where access to a dark narrowband wavelength-division multiplexing (WDM) optical channel is provided over a wavelength division multiplexed fiber network that is managed at the physical level, but unlit by the network provider. This is typically done using coarse wavelength division multiplexing CWDM because the wider 20 nm spacing of the wave bands makes these systems much less susceptible to interference.
[edit] References
- Geert Lovink, Dark Fiber: Tracking Critical Internet Culture, MIT Press, Cambridge Mass, 2002 ISBN 0-262-12249-9
