Why is latency and bandwith separated? If latency is delay of data, and bandwith is data over time, shouldn’t one affect another? If it takes 5s for a car to start, and 10s to reach it’s destination, then the average speed would be spread out across the whole 15s. Should this not be the same?

Question

Why is latency and bandwith separated? If latency is delay of data, and bandwith is data over time, shouldn’t one affect another? If it takes 5s for a car to start, and 10s to reach it’s destination, then the average speed would be spread out across the whole 15s. Should this not be the same?

In: Technology

Answer 1

A good, real world way to understand it would be to look at satellite internet, using geostationary communication satellites, 36,000 km out in space. With a big dish and an expensive plan, you can get high bandwidth out of this. Gigabytes of data send up and down.

But if you send a message, you can’t get around the fact that it takes 0.12 seconds for the signal to get from your dish to the satellite, another 0.12 seconds for it to get back down to the base station, and the reply to your message takes 1.2 seconds to get back up to the satellite and 1.2 to get back down. If all the other stuff with your local router, the satellite hardware handling your data, the terestrial link to and from the server, and the sever servicing your request happens instantly, you still have 0.5 seconds of lag. In practice, lag usually pushes out to a second.

But because your bandwidth is high, it when that message comes, you it can contain lots of data. There can be a 20Gb/s stream of data that comes in, one packet after another. And, yup, that means there will be 5Gb of data ‘in flight’ between the ground station and you at any time. If you sent a message that said ‘stop now’, there’d be a 0.5 second delay, and 10Gb of data.

This is fine if you are streaming a movie, or downloading a large file. But web pages often use many different parts, and lots of these parts tell your browser to download other parts. This costs you lots of those second-long delays – meaning that a custom proxy is essential, one that renders the page at the ground station and sends all the page data in one stream. Phone services are annoying, but workable at a pinch. Gaming is right out.

So this explains how a service can have high bandwidth but low latency. The two features of a connection are quite separate.