Once the true velocity (v) of the light inside the fiber is known, calculating the latency (delay time) is a simple kinematic equation: Time = Distance / Velocity. Conversely, if an engineer requires a specific time delay, they can calculate the exact physical length of the fiber. Latency is a term that is used to describe a time delay in a transmission medium such as a vacuum, air, or a fiber optic waveguide. In free space, light travels at 299,792,458 meters per second. When transmitting over. However, when light enters a physical medium like the silica glass core of an optical fiber, it slows down. This reduction in speed is determined by the material's Group Refractive Index (n). It measures both one-way latency and round-trip time (RTT), factoring in the speed of light in fiber and delays from network equipment such as routers and switches. This. Latency in fiber optics refers to the delay time, or 'time delay', it takes for a light signal to travel from the transmitter at one end to the receiver at the other, factoring in the calculation of fiber latency which includes the speed of light in the fiber, the index of refraction, and the. If latency is too high it spreads data packets over the time and can create an impression that an optical metro network is not operating at data transmission speed which was expected.