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.

Queuing delay

Amount of time the incoming packet is waiting in the queue until it can be processed.

Processing delay

Amount of time required to process the packet header, check for bit-level errors, and determine the packet’s destination.

Transmission delay

Amount of time required to push all the packet’s bits into the link, which is a function of the packet’s length and data rate of the link.

Propagation delay

Amount of time required for a message to travel from the sender to receiver, which is a function of distance over speed with which the signal propagates.

Latency is the time it takes for a message, or a packet, to travel from its point of origin to the point of destination

Latency is expensive—literally and figuratively