# Homework Help: Networking speed

1. Oct 2, 2009

### Cyborg31

1. The problem statement, all variables and given/known data

I would like to send a packet of size 1500 kilobytes from point A to
point B. There are a total of 3 links that it has to cross, of length 1000,
2000, 3000m respectively. The bandwidth on those links is 100, 1000,
and 500 kilobytes/second. Assume that there is no processing time,
but they have to wait about 1 second at each intermediate router due
to congestion. Assuming that a bit travels at about half the speed of
light in the medium, and that a router must have the entire packet
before it can process it, how long must I wait to get my packet?

2. Relevant equations

3. The attempt at a solution

I'm just trying to see if I'm understanding this correctly.

If Router A to Router B has a 1000m physical link with a bandwidth of 100 KB per second, then it takes 1 second to push 100 KB of data on to the physical line (of 1000m length). Once it is pushed on the physical line, and I have calculated that one bit takes 0.0000067 seconds to travel 1000m, that 100 KB of data takes 0.0000067 seconds to travel to Router B (which is 1000m away).

There is 1 second in congestion delay so it'd take 2 seconds (one second to push it on the line and one second in queue) + 0.0000067 seconds of physical travel tie for every 100 KB of data from Router A to Router B. So total time from A to B is 15 * (2 + 0.0000067) seconds.