# What is the the relation between the amount of data transmitted and line distance?

I am wondering what is the relation between line distance and the amount of data transmitted on that line. I know only the basic of computer science. Let's say I want to calculate the time it takes for 100 GB to transfer over a line with the speed of 100MBps. If I just divide them, I will get 1000 seconds but in my online class, the lecturer said the time depends on the line distance. Since it is an introductory course, he doesn't explain anymore. So my question is, how is it relevant and why? I know the simple answer should be the resistance of the line increase as it got longer but does the resistance affect on the needed time significantly? How could I calculate the needed time with distance?

• Beware differences between bits, bytes (and possibly octets). – greybeard May 13 '20 at 22:41
• If you are on earth and the receiver on the moon, add about 1.3 seconds to the time :-) – gnasher729 Nov 11 '20 at 11:39

Distance sets lower bounds on latency, the effect on throughput as opposed to data rate depends on protocol.
Raw error rate increases with distance.

• Coincidentally, EM signals take, on average, 499 seconds to travel between earth and sun. The moon has successfully been used as a reflector - if it was possible to have signals reflected at some "surface" of the sun, 1000 seconds from transmission start to reception end would amount to something, while half an hour couldn't possibly get you an answer. – greybeard May 13 '20 at 22:52

You wrote

I know the simple answer should be the resistance of the line increase as it got longer but does the resistance affect on the needed time significantly?

but this is not about the resistance of the line.

Consider again the statement

the lecturer said the time depends on the line distance

So the question is how long it takes to transfer/communicate $$X$$ amount of data (100 Gbit, let's say) if the line speed is 100 MBit/s). You think it may be just 1000 s (amount of data divided by line speed).

But the point about the line distance is that it takes a finite amount of time for the transmission to go through the line. This is called latency. For example, if it takes 10 s to go through the line, then the answer is 1000+10s = 1010s.

Knowing both the data rate (line speed) and latency (line distance), allows you to answer the question of how long it takes.