High-Performance Browser Networking

But to keep it simple, the rule of thumb is to assume that the speed of light in fiber is around 200,000,000 meters per second, which corresponds to a refractive index of ~1.5.

The good news is the speed of light is high: 299,792,458 meters per second, or 186,282 miles per second. However, and there is always a however, that is the speed of light in a vacuum. Instead, our packets travel through a medium such as a copper wire or a fiber-optic cable, which will slow down the signal (Table 1-1). This ratio of the speed of light and the speed with which the packet travels in a material is known as the refractive index of the material. The larger the value, the slower light travels in that medium.

The total latency between the client and the server is the sum of all the delays just listed.