Networking Kid / Why It Is Slow Or Broken

Latency And Bandwidth Are Not The Same Complaint

Most everyday slowness is about waiting, not about width.

Bandwidth is how much can be carried at once, like the number of lanes on a road. Latency is how long one thing takes to make the trip, like the length of the road. They are independent quantities, and the marketing you have been exposed to talks almost exclusively about the first one because it is the easier number to sell. That is unfortunate, because for most of what people actually do all day the second matters more. Loading a page is not one large transfer. It is a conversation of many short exchanges, each of which has to wait for the previous answer before it can even begin.

This is why the physical distance to whatever you are talking to is so decisive. Signals move extremely fast but not instantly, and every exchange pays the round trip twice, once going out and once coming back. Multiply a long round trip by many small dependent exchanges and you get a page that crawls on a connection with enormous advertised capacity. Adding lanes to a very long road does not shorten the road. This single insight explains more everyday disappointment with internet performance than any other fact in this issue.

Once you have this distinction, a lot of confusing experience resolves itself. A large download that starts slowly and then runs beautifully is a latency story followed by a bandwidth story. A video call that stutters while a download runs happily beside it is a timing story, not a capacity one, because the call cares about when each piece arrives rather than how many arrive. And a connection that tests well on a capacity measurement while feeling sluggish in daily use is not lying to you. It is answering a question you did not mean to ask.