Fiber Optic Path

Fiber distance, or the fiber-optic path is often the largest source of network latency This especially true in networks spanning 100’s to 1000’s kilometers where latency is unavoidable, but can be minimized. Speed of light in a vacuum is measured at 1 foot per nanosecond or 3.28084 μs (microseconds) per kilometer. With the limitations imposed with how light travels along optical cable, it is generally estimated that latency on one kilometer of optical cable is five microseconds (5 μs) although, other factors such as the fiber quality may influence the total latency across the fiber optic path.

Fiber quality

Length of fiber and fiber quality can impact latency and introduce other losses in the fiber. Access to a direct path can reduce the length of the fiber and subsequently reduce latency. In addition, the use of low quality EDFA amplifiers can increase latency.

Fiber Route

Fiber does not necessary travel in a straight line between the origination and termination points. In an example of a short fiber optic network (140km), there was a difference of 14 kilometers between exiting fiber route, and an alternative optical infrastructure provider. This difference in distance is equal to approximately 140 μs (microseconds) round-trip of additional latency.

Often, switching fiber-optic service providers is not cost effective (or contractually not possible) but it still may be possible to look at other possible sources of latency such as the Network Equipment or Network Design, to reduce overall network latency.

Other Sources of Latency

Network Design

The network routing/switching and resilient path design.

Networking Equipment

The latency introduced by the fiber networking equipment.

See XKL's full Latency Test Report