Unused fiber; Fiber that has been installed but is reserved for future use. Carrying no light.
Dark fiber is fiber optic Cable that has not been used yet and is not connected to any device. Dark fiber is usually installed to avoid the expense of having to go back and lay fiber again later. The abundance of dark fiber in the U.S. occured in the 1990s when there was a large upswing in the telecom and computer industries. Companies with installed dark fiber often lease it out to other companies and/or providers.
n the past, dark fiber was virtually never sold. Telecommunications companies considered it their core asset, and selling it would be akin to selling off their business. Due to an incredible glut in the market, however, selling dark fiber has become extremely viable and is now a practice of many major telecommunications companies.
Q) What is dark fiber?
Dark fiber is optical fiber, dedicated to a single customer, where the customer is responsible for attaching the telecommunications equipment and lasers to "light" the fiber. Traditionally, optical fiber networks have been built by carriers which they take on the responsibility of lighting the fiber and provide a managed service to the customer.
With dark fiber networks, the end customer controls the actual fiber and chooses the service provider to whom they wish to connect for services such as telephony, cable TV and Internet.
Professional third party companies who specialize in dark fiber systems take care of the actual installation of the fiber and also maintain it on behalf of the customer. These companies own the fiber, but grant IRUs (Indefeasible Rights of Use) for a contractual period for unrestricted use of the fiber.
There is no additional management complexity or overhead associated with dark fiber. In fact, in many cases dark fiber may be more reliable than traditional telecommunication services and easier to manage because it vastly simplifies the network architecture and allows the consolidation of network services to a central hub.
In addition dark fiber provides for increased competition among service providers and levels the playing field amongst all service providers for the delivery of telecommunication services. With dark fiber, customers build networks to carriers rather than the traditional model where carriers build networks to customers.
Q) How reliable is dark fiber?
Dark fiber can be more reliable than traditional telecommunication services, particularly if the customer deploys a diverse or redundant dark fiber route.
Dark fiber is a very simple technology. It is often referred to as being technologically neutral. Sections of dark fiber can be fused together so that one continuous strand exists between the customer and the ultimate destination. As such, the big advantage of dark fiber is that no active devices are required in the fiber path. Since there are no active devices dark fiber in many cases can be more reliable than a traditional managed service. Traditional managed services usually have a myriad of devices in the network path such as SONET multiplexers, Add/Drop multiplexers, ATM switches, routers, etc. Each one of these devices is susceptible to failure which is why traditional carriers have to deploy complex networks and systems to insure reliability and redundancy.
Many customers assume that because the carriers deploy SONET rings they have a reliable network. In fact, SONET rings are generally only deployed between carrier central offices. Most customers today, except in exceptional circumstances, only have one unprotected link to their nearest central office. This is the single weakest link in their network.
For the greatest reliability, many customers will install 2 separate dark fiber links to 2 separate service providers. Even with the additional fiber for redundancy, dark fiber networks are cheaper than managed services from a carrier.
With dark fiber customers have a number of choices in terms of reliability and redundancy:
• They can have single unprotected fiber link and have the same reliability as it exists today with their current carrier;
• They can use alternative technology, such as a wireless link for backup in case of a fiber break; or
• They can install a second geographically diverse dark fiber link whose total cost is still cheaper than a managed service from a carrier.
Because fiber has a greater tensile strength than copper or even steel, it is less susceptible breaks from wind or snow loads.
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Q) Does dark fiber increase my network management costs and complexity?
Network cost and complexity is significantly reduced with dark fiber in a number of ways:
• Dark fiber has no active devices in the path as in a typical carrier network, therefore are fewer devices to manage and less thing that are likely to go wrong;
• Repair and maintenance of the fiber is generally included in the service contract from the fiber provider. These companies are in many cases the same companies that carriers use to maintain their fiber;
• Dark fiber allows organization to centralize servers and/or out source many different functions such as web hosting, server management, etc.
A fiber network allows large enterprise customers, universities and schools to essentially extend their in house LANs across the wide area. Because there is no effective cost to bandwidth with dark fiber the long distance LAN can be still run at native speeds with no performance degradation to the end user. It is therefore very simple to relocate a server to a distant location where previously it required close proximity because of LAN performance issues.
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Q) Who manages and repairs the dark fiber in case of breaks or other problems?
In most cases management of the fiber is included in the service contract from the fiber provider. In many cases these are the same companies who maintain and repair for the major carriers. They offer the same terms and conditions to dark fiber customers as they do for the major carriers.
In many cases the companies that installed the fiber are also the ones who maintain the fiber. These companies will also look after any on-going moves, adds and changes as well as relocating the fiber in case of road construction and so forth.
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Q) What about moves, adds, changes and fiber relocation services?
Moves, adds and changes are generally carried out by the fiber provider on a routine basis. Most moves, adds and changes only require breaking and fusing together existing fiber pairs. The work can be done on an hourly rate, or priced on a per move, add or change basis. The cost, terms and conditions for moves, adds, changes are usually included in your fiber maintenance agreement.
On very rare occasions fiber has to be relocated because of road construction or repair. Usually the city that had undertaken the road work will pay for the majority of the fiber relocation costs. However, if this not case, minor relocations of several hundred meters are usually included as part of the maintenance contract.
If a major relocation is required most contracts give the customer the option paying their share of the relocation expenses in proportion to the number of fibers they own in the cable or canceling the fiber contract.
Although uncompensated fiber relocations are very rare, it is a factor they should be taken into account when procuring dark fiber.
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Q) Is fiber the same fiber used by the carriers?
Yes. In most cases for metropolitan and long haul fiber the most common of fiber by carriers is Single Mode Fiber (SMF-28). This is usually adequate for most fiber installations. For particularly long spans or long distances, specialty Non-Zero Dispersion Shifted Fibers (NZDSF) are used. But given the cost difference, single mode fiber is generally the fiber of choice for most fiber installations.
All splices are performed with an industry-accepted fusion splicing machine and the customer is provided with testing documentation reflecting bi-directional losses by fiber and installed span loss by fiber.
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Q) What happens in case of fiber break?
Fiber breaks are very rare and typically any given span of 10 km of fiber will suffer an average of less than 5 minutes of outage due to breaks in a year.
If there is a fiber break, the fiber provider will specify an average repair interval. The repair interval for aerial fiber is usually much shorter than buried fiber. A normal fiber break outage for aerial is 4 hours and 6 hours or longer for buried fiber. However these are average repair intervals. With buried fiber, in particular, where there may be water and mud the repair time can be considerably longer.
The fiber provider will splice fibers tube by tube or ribbon by ribbon or fiber bundle by fiber bundle, rotating between tubes or ribbons operated by the separate users of the cable, including the customer, in accordance with a priority and rotation provided for in the maintenance contract. In general, priority among users of the fiber cable affected by a cut shall be determined on a rotating restoration-by-restoration and segment-by-segment basis, to provide fair and equitable restoration priority to all users of the cable, subject only to such restoration priority to which is contractually obligated by the fiber provider.
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Q) What are carrier neutral collocation facilities?
In many cities, companies are building facilities to allow the interconnection of networks between competing service providers and for the hosting of web servers, storage devices, etc. They are rapidly becoming the obvious location for terminating customer owned dark fiber.
These facilities feature diesel power backup systems and the most stringent security systems. The facilities are open to carriers, web hosting firms and application service firms, internet service providers, etc.
Most carrier neutral open collocation facilities feature a "meet-me" room where fiber cables can be cross-connected to any service provider within the building. With a simple change in the optical patch panel in the collocation facility the customer can quickly and easily change service providers on very short notice.
Many of these concepts of carrier neutral collocation facilities were first developed with the next generation Internet programs in the United States and Canada with a concept called a GigaPOP. Leading researchers and universities recognized that there were many benefits to interconnecting to carriers at a common "meet me" point. So rather than having multiple carriers build separate facilities to university campuses, the universities instead built one single telecommunication facility to a GigaPOP and then interconnected to one or more carriers on a new demarcation point that was not on the customer premises.
When selecting a fiber provider, care should be taken to see if their fibers terminate at carrier neutral collocation facilities. Some fiber providers only terminate their fiber in their own central offices which makes it difficult to interconnect to other service providers or attach your own equipment to the fiber.
Carriers looking to increase their network capacity can look to the FiberRing Dark Fiber Service to satisfy the demand for today´s bandwidth-intensive applications. Dark Fiber Service is POP-to-POP backbone fiber capacity that is offered for sale.
A Dark Fiber is a fully transparent, unprotected Dark Fiber.
Dark Fibers are sold as full circuits, which means that they are provided on FiberRing´s wholly-owned and operated facilities. A Service Level Agreement is available for wavelength service and can be customized for each customer.
Customers of the FiberRing Dark Fiber Service are responsible for installing the networking equipment and providing clocking, monitoring, network management, customer service, and all other services. Due to the fact that the interconnect distance is short, FiberRing will offer colocation in conjunction with the Dark Fiber service.
FiberRing Dark Fiber Services are sold as separate offerings:
* Indefeasible Right of Use (IRU) Services (15 years)
* Long term Capital Lease (10 or 15 years)
* Short-term Lease (1 to 5 year)
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