Fiber Characteristics that Affect Latency

Fiber-optic communication is a method of transmitting information from one place to another by sending pulses of light through an optical fiber. This is important to note when discussing the variables that affect latency.

Distance

The definition of zero network latency would be network transport at the speed of light. That said, the further the light has to travel the higher the latency. Obtaining just a fiber connection from point A to point Z is no longer sufficient to ensure optimal data transfer speeds.  Fiber networks do not normally follow a direct line between any given "A" and "Z" location.  It follows geographic contours relating to roads, railroad tracks, or other types of right-of-way where the fiber was placed. For this reason it is important to understand the exact route your circuit follows. You want to eliminate any wasted distance. For dark fiber as well as lit circuits, that is not an option for a typical service provider, as they are quoting their circuits on an existing fiber path that in most cases cannot be varied.  However, a network integrator that can utilize optimal spans from multiple providers will be able to piece together the most direct route, incorporating new fiber construction where required.

Reaching the end of the Fiber

In the longhaul environment, there are two main options for extending the transmission of light through the fiber; optical amplifiers and regenerators. Amplifiers and Regenerators are placed along the fiber optic route to ensure that the signal is able to travel the distance while keeping its' integrity. The main difference between the two is that an amplifier adds light to the existing wavelength to increase the strength of the signal with very little added latency, whereas a regenerator will add a substantial amount of latency. This is required for both lit and dark fiber solutions and needs to be taken into consideration as it is a highly variable component of the end-to-end circuit that affects latency.

What is Dark Fiber?

Dark fiber is a term used to describe fiber optic strands that are not being used - i.e. there is no equipment on the ends of the fiber. The amount of dark fiber, particularly in the United States, increased dramatically over the past decade. Dark fiber is contrasted with active fiber optic cable, often referred to as "lit" fiber.

In 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 what has been referred to by many as a "glut" of fiber in the marketplace, along with a need to generate revenue, selling dark fiber became more common and is now a practice of a few telecommunications companies. The reality though is that many providers are still reluctant to sell dark fiber and will only offer lit circuits.

In some markets where there is a large supply of dark fiber, prices have been driven down to levels at which many companies that traditionally bought lit circuits are finding it practical to purchase wholesale dark fiber and light it with their own equipment. Many Enterprise, Government, and Educational Institutions that have high-bandwidth needs are now looking to dark fiber as a means to find economies of scale by owning & operating their own network as opposed to purchasing multiple lit circuits. Unfortunately, because so few telecom companies still sell dark fiber, the available dark fiber route may be much longer than an alternative lit circuit path from another provider

Latency of Dark Fiber and Lit Fiber

When evaluating the value of dark fiber the most important issue is the economics. Dark Fiber requires a large upfront Capital Expense for transmission equipment plus the cost of the dark fiber, but allows you to add additional bandwidth capacity at nominal incremental cost beyond your initial investment. A lit circuit will be a leased asset and will fall to the Operational Expenses of the company, but as your bandwidth needs grow, each additional circuit is a 100% incremental cost.

So if cost is not your primary consideration, which option would offer the lowest latency? It is a popular misconception that Dark Fiber always has the lowest latency between two points - it can be in some instances, but there are many times when a lit circuit is the better choice when low latency is an absolute priority due to a shorter circuit path and/or better equipment configuration.

Case Study:

When working with a top trading firm their main goal was to drive the lowest latency circuit they could between two locations. They came to CFN Services and requested pricing for dark fiber strands. After a thorough evaluation of both dark fiber and lit circuit provider options to connect various "A" and "Z" address pairs, in most cases the shortest available dark fiber path would have higher latency than the lit circuit path:

Sample Data Analysis

NOTE: Information above was created utilizing FiberSource®. For each Dark Fiber Route, the availability for resale of the Dark Fiber was taken into account. These mileages are the lowest available.

As you can see, the dark fiber span provided a distance advantage in only a handful of the spans analyzed, so in some cases going with dark fiber would cost the firm undo latency increase.

There are times that dark fiber is the best solution and times that a lit solution is ideal. In order to be equipped with all the information you require to make these decisions, you need to ensure you work with a network integrator like CFN Services.  FiberSource® Advisor provides you not the information from over 550 Global dark and lit carrier providers, collocation providers, utilities and all lit buildings; but also the professional services of CFN to interpret and analyze the data to give a complete picture of all routes.  CFN Services is a carrier neutral network integrator who can utilize optimal spans of all available fiber between locations to provide the lowest latency, highest performing network available.