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Dark fiber definition

The term “dark fiber” is not to be confused with a “dark network”. It simply refers to unused fibers in an already installed optical fiber cable, so another common name for dark fiber is “un-lit fiber”.

Dark fibers are typically deployed by network infrastructure owners, such as telecommunication operators who provide both fixed and mobile services. The installation of a fiber optical cable is a costly exercise thus providers typically install many more fibers than their initial need. These surplus, unused fibers are referred to as dark fibers and can serve two main purposes: they can be reserved for future use by the owner, or they can be sold to other parties in need of high-capacity connections between two destinations. This practice helps reduce the need for frequent infrastructure installations, which, in turn, benefits both costs and the environment.

Dark fiber can be effectively utilized in both metro fiber networks (for short-range connections) and long-haul fiber networks. In the metro, it is often used to extend individual services from data centers. Long-haul dark fiber is typically activated with DWDM equipment, including lasers, transponders, and in-line amplifiers.

What is dark fiber in telecom?

As previously mentioned, in telecommunications, the term “dark fiber” refers to installed but unused optical cables designated for future data transmission. When active, these fibers carry data through light signals, but when inactive, they remain “dark”.

Let’s talk about a couple of key values related to dark fiber in the telecom industry: 

  1. Future-ready capacity: Telecommunication companies often install more cables than necessary to ensure future-proof planning and efficiency. Consequently, activating dark fiber can be a relatively swift process that minimizes the environmental impact.
  2. Network control: Dark fibers empower customers with a high level of control over their traffic and the routes it takes. You will know the traffic speed and routing, allowing you to have full control over your network's performance.
  3. Scalability: Scalability is a key advantage of dark fibers, as it provides the owner or leaseholder with full control over the implementation time and cost of adding capacity to already lit fiber. This is achieved by adding or upgrading the equipment used to activate the fiber, so network expansions can occur at your own pace.
  4. Security: Leasing dark fiber offers organizations the opportunity to not only know where their traffic is flowing but also to have control over all the equipment used to transmit that traffic. Fiber cuts and outages are inevitable, so organizations establish resilience by constructing networks over different fiber routes.

What is dark fiber used for?

Some typical use cases of dark fiber based on various purposes within the telecommunications and networking industry:

Telecommunication networks:  Internet Service Providers (ISPs), Content Delivery Networks (CDNs), regional, national, and international telecom operators use dark fiber to connect their hubs and data centers. They also use it for data exchange with other operators through peering arrangements. When traffic volumes increase, these entities purchase dark fiber to expand their networks beyond their existing fiber footprint.

Content networks: Content providers and cloud operators are among the biggest consumers of dark fiber today, often using multiple dark fibers to connect their datacenter campuses, transporting massive data loads.

Enterprise/governmental networks: Large enterprises and governmental organizations often lease dark fiber to enhance network security and reduce latency. This allows them to establish private, high-capacity connections between their internal sites and to connect to data centers or cloud providers.

Data Center connectivity for cloud: Not all cloud data centers are located close to their customers. High-speed fiber solutions can bring cloud services closer to city centers where enterprises have their operational needs.

Mobile back-haul: The most effective way to connect mobile base stations is by running dark fibers directly to the antennas. In many cases, these fiber cables are purpose-built. As more mobile operators share antennas, this approach becomes a cost-effective way to build networks. 

We at Arelion have long experience in this area, doing heavy lifting for our loyal customers.

Learn more about optical and dark fibers by Arelion.

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