Suppose there was a single strand of perfect fiber optic cable that stretched all the way around the world and ended up back where it started. How long would it take a signal to circumnavigate the world through the cable and end up back at its point of origin?
Light is very fast. In a vacuum it travels at about 186,282 miles per second. In fiber optic cable, because of the refractive index of the material, it travels more slowly: approximately 124,188 miles per second. The Earth’s circumference is 24,901 miles. So, in our world-spanning cable, light would complete its journey in about 0.2 seconds. In a perfect world, you could transmit a signal to the other side of the world and back again in a fifth of a second. Unfortunately, reality does not match the theory, and on the real Internet, there are many obstacles through which a signal has to pass before it gets to where it’s going and back again.
Firstly, there is no such thing as the perfect fiber optic cable: signals degrade and have to be boosted, much of the “last mile” and various other parts of the road along which a signal travels are not fiber optic cable, but copper cable, through which signal propagate more slowly.
Additionally, on the Internet, no data ever travels a straight line path between its source and destination. It is routed between many different points, passing through dozens of routers and switches as it travels. Each node in the network imposes a little extra delay in the signal’s progress. Some of these routers may be many years old, some of them may be overloaded, further slowing down the signal.
These and many other obstacles each add fractions of a second to the length of a signal’s journey. To a person trying to load a website, the cumulative effect of all those fractions of a second is a frustrating wait for their page to appear.
While in theory, data travels the globe at the speed of light, in practice, round-trip times – the time between a browser requesting data and that data arriving – can be frustratingly long, creating significant delays for web users. Even communication between relatively close points on the network, the east and west coasts of the US, can experience several-second delays because of slow networks. Those delays often translate into reduced engagement by site users, reduced conversions, and higher bounce rates.
Content distribution networks are designed to combat the effect of excessive round-trip times. CDNs are a form of caching. Instead of all of a site’s assets being distributed from one point of the surface of the Earth to every visitor, they are cached ahead of time on many servers distributed at dozens of points around the globe. When a browser makes a request for data, that request can be routed to the nearest of these “edge-servers,” reducing the round-trip time enormously.
Cutting load times should be a prime concern for web masters. Content distribution networks are a key component of a strategy for minimizing load times and, therefore, increasing conversion rates and user satisfaction.