Why times elapsed connecting to a server are different?

Question

I have a small program which connects to a server of my choice and measures the time elapsed to do so. Each time I run it it returns different result. My question is what does this time depend on ?

Network congestion for one.

If I choose a server that has multiple addresses e.g. google.com the length of physical link may differ from time to time ? Is it safe to assume that it also affects connection time ?

Are there any other factors in place ?

Answer 1

You might want to read about how Internet works and how packet switching works to add to the explanation here.

But for now, lets assume things are purely between your PC, to a very specific host server that you have the IP address.

The way packet switching works is "try our best" to send packets to the destination.

If for whatever reason the switches/routers between your PC and the server has issues (too much traffic on it, or it dies) it will simply try to route the packet using different route. The same request may ends up coming through multiple different routes just because it happens to be the better route 'at that time'.

Or if the router/switch that your packet arrives to is too busy, that router WILL drop your packets, and send a confirmation to your PC that they dropped it. Your PC will then re-send the packet, hoping it will arrive. (This whole process is completely transparent and you won't see it unless you know what you are doing / looking for)

Different physical link will definitely affect time elapsed, not only because you may be not on the most straight-line route, but also, maybe the straight-line route is highly congested and you may ends up faster using the route going round the world first.

For comparison, imagine you are driving your car from A to B. Same driving speed, same road, you still end up with different time elapsed due to network congestion. Then one day you decided to use different road. The smaller road, the backroad, the highway, you name it. You may arrive faster / slower - you really don't know. You may have an 'average' time, but the time elapsed will still be different.

Hope this helps.

Answer 2

When it comes to network speeds, there are a lot of factors. Distance, latency, bandwidth, congestion, route, etc. Any one factor can be a bottleneck. Then there is the device/server itself. It can be overloaded with traffic, busy doing other requests, etc...