Optical Transport: How It Works and What OTN Is Used For
A growing company opens a new branch, then waits months for the site to join its network. Leased lines take time to order, and each one adds a monthly bill that keeps climbing. As a result, new projects slow down and costs rise. Meanwhile, businesses send more data every year. Based on the Ericsson Mobility Report, global mobile network data traffic grew 22 percent between Q1 2025 and Q1 2026 and reached 210 exabytes per month, and one exabyte equals one billion gigabytes. Optical transport offers a way to carry much more data between sites without constant upgrades. To use that option well, teams first need to understand how it works. The right provider matters just as much, because a suitable provider improves network performance, supports growth, keeps services reliable, and gives an organization more control over its infrastructure. Understanding starts with the basic definition. What is optical transport? Optical transport is the technology that moves data as light signals through optical fiber, a thin glass cable. Because light loses very little strength inside the fiber, signals travel long distances with few interruptions. This approach differs from general data transmission, which is a much wider term. Optical fiber transmission stands out because it carries far larger volumes of data and keeps performance steady. The next section follows that light between sites. How does optical transport work? In practice, optical transport works by turning electrical data into light, sending that light through the fiber, and turning it back into data at the destination. First, a transmitter, usually a laser, creates the light pulses. Then amplifiers boost the signal along long routes so it stays strong. Finally, a receiver at the far end reads the light and restores the data that servers and routers can use. One more technology makes this process far more efficient. Wavelength Division Multiplexing, or WDM, sends many signals through one fiber at the same time, and each signal uses its own wavelength, which means its own light frequency. As a result, one fiber carries many channels instead of one. To manage all this traffic, networks often rely on a common standard that people call OTN. What is OTN used for? That standard, OTN, is used to carry, combine, and manage digital traffic across fiber networks. The name stands for Optical Transport Network, and the ITU, a United Nations agency for telecommunications, publishes the standard. First, OTN merges many small services into larger channels, which people call traffic aggregation. Second, it watches performance and spots errors, so operators can find and fix faults early. Third, it lets operators track each customer service on its own, which supports service management. OTN technology therefore appears in telecom core networks, data center links, and large company networks. OTN belongs to the broader practice of moving data over light, but the two are not the same thing. The broader practice includes OTN as one specific standard, so a network can still run without it. Both aim to move data efficiently, which leads to the benefits below. What are the main benefits of optical transport? Together, WDM and OTN give optical transport four main benefits: high capacity, long reach, room to grow, and clear visibility, though each setup differs. Here are the details Optical transport vs. Dark fiber: What’s the difference? Beyond those benefits, optical transport differs from dark fiber in one simple way: Optical transport is the technology that sends data over optical networks. Meanwhile dark fiber is the physical fiber that carries no signal yet. People also call dark fiber unlit fiber, because no active transmission equipment sits on it for the customer’s use. A business that leases dark fiber adds its own equipment, so it decides its own capacity, wavelengths, and security rules. This control can ease the delays from the opening example. Dark fiber infrastructure supplies the physical layer, and the customer’s equipment turns it into a working network. Those networks appear in a few common places. Where is optical transport used? Once the fiber is lit and managed, optical transport serves telecom core networks, data center connections, and cloud links for offices. For example, data center interconnects, or DCI, link two or more data centers for backup, data copying, and shared workloads. Likewise, cloud links connect offices to cloud platforms. All three uses depend on enough fiber capacity and suitable routes. If a route has little spare capacity, growth stalls. If a path is indirect, it adds delay, which people call latency. Because of these limits, fiber choice deserves careful attention. Choosing the right fiber infrastructure for optical transport Good fiber for optical transport offers route diversity, spare capacity, wide reach, and access to data centers. Route diversity means separate physical paths, so one cable cut does not stop service. Reach covers the cities and countries a provider connects. Data center access shortens the path to where networks exchange traffic. These factors matter most when a project spans several cities or countries. In that case, each coverage gap or shared route adds risk and cost. The final section shows one provider with this kind of coverage. Choosing the right fiber infrastructure partner The right fiber decides how far a network can grow before it needs a redesign. As a result, organizations that plan optical transport around dependable routes and spare capacity avoid costly changes later. ARNet is one example of a provider that supports these needs. It provides fiber infrastructure for organizations deploying modern network designs. Its dark fiber solutions include metro fiber for city networks, long haul fiber between cities and countries, and last mile fiber, which connects a final site to the wider network. ARNet operates across Malaysia, Indonesia, Singapore, and Thailand, and the network coverage page lists its routes. For more details, visit the ARNet website. Organizations choose ARNet for reliable connectivity, scalable fiber infrastructure, and consistent performance across a regional footprint. This strong infrastructure foundation suits AI networking, where data centers need high-capacity links to share large workloads. As data demands and digital
Dark Fiber for Data Center Interconnect: A Complete Guide
Network traffic can become harder to manage as a company adds more applications, cloud services, storage, and data. When more data needs to move between different locations, an existing network may not have enough capacity. This can make expansion harder and increase network costs. A data center interconnect can help by connecting separate data centers through a dedicated fiber link. The right network can make it easier to handle more data as needs grow. It can also give teams better control over their connections and help them plan for future needs. For this reason, it is useful to understand how data center interconnect work and how dark fiber can support it. The first step is to understand what dark fiber means. What is dark fiber? Dark fiber is unused fiber that has already been installed but is not carrying data. For a data center interconnect, a company can lease this fiber and use its own network equipment to send data through it. The fiber provider takes care of the physical fiber route. The customer manages the equipment that sends data through the fiber. This gives the customer more control over the network and the capacity it uses. This is different from a lit fiber service. With lit fiber, the provider activates the fiber and manages the connection for the customer. With dark fiber, the physical fiber and active network equipment are managed separately. What is a data center interconnect? A data center interconnect is a network connection that links two or more data centers. It allows them to exchange data, applications, storage, and other network services. For example, a company may have one data center for its main systems and another for backup. The connection between them allows data to move from one site to the other. This can support backup, disaster recovery, cloud services, and other workloads. Cisco also describes DCI solutions that connect data center equipment through high-speed optical links. This shows how fiber can provide the connection between separate data center locations. With this basic idea in place, the next step is to see how dark fiber fits into the connection. How dark fiber and DCI work together? Dark fiber provides the physical path between two locations. Optical equipment then sends data through that path. In a data center interconnect, network equipment at each data center connects to optical equipment that sends signals across the fiber. The equipment used for the data center interconnect depends on the distance and capacity needed. A short connection may use a simple optical link. A longer connection may use DWDM, which lets several signals travel through the same fiber pair. Cisco’s DCI documentation shows that 400G optical connections can run over dark fiber. Its point-to-point design can cover up to 40 km without amplification and can reach much farther with the right equipment. This means the fiber provides the path and the equipment controls how data moves across it. This separation gives organizations more choice when planning their network. Benefits of using dark fiber for DCI Dark fiber gives organizations more control over their data center interconnect network. It also gives them more room to grow as they need to move more data. Here are some of the main benefits: These benefits make dark fiber useful for organizations with growing data needs. Still, dark fiber is not the only data center interconnect option. The right choice depends on the organization’s network needs, budget, and future plans. How much bandwidth does dark fiber DCI support? Dark fiber does not have one fixed bandwidth limit. The capacity depends on the optical equipment, distance, fiber quality, and network design used for the connection. Modern optical equipment can support 100G, 400G, 800G, and higher speeds for data center interconnect (DCI). Multiple wavelengths can also be used on the same fiber pair to increase the total capacity. The actual capacity depends on the equipment and network design used for the connection, according to Cisco and Nokia. This means the same fiber route may support higher capacity later if the optical equipment used for the data center interconnect is upgraded. As a result, the physical fiber does not always need to be replaced when traffic increases. Why does future data growth matter? Data use continues to grow across digital networks. According to the Ericsson Mobility Report, global mobile network data traffic passed 220 exabytes per month in Q2 2026 and grew 23% from the same period a year earlier. This figure is for mobile traffic, not DCI traffic, but it shows how much data is moving across networks. For a data center interconnect, this wider growth is a useful reason to plan for future capacity instead of focusing only on current traffic. That is why capacity planning should be part of the network decision from the start. Planning ahead can make future upgrades easier and reduce the need for major network changes. Key features to look for in a dark fiber DCI network When choosing a data center interconnect fiber network, there are several important points to check: These points help teams look beyond the first connection. They also make it easier to compare different providers using the same requirements. Deployment challenges to consider Dark fiber can provide strong network control, but it needs careful planning. The fiber route is only one part of the solution. Organizations also need the right optical equipment, power, cooling, monitoring, and technical support. Distance is another factor. Longer routes may need extra optical equipment or amplification. Fiber quality can also affect the distance and speed that the connection can support. For a data center interconnect, teams should review the fiber route and optical design at the same time. A route may look suitable based on distance alone but may need extra equipment to reach the required capacity. Good planning at this stage can help avoid changes later. It also makes the next step, choosing a provider, easier. Choosing the right fiber infrastructure partner The right data center interconnect solution should