On numbers 3 and 4, I am not sure how to compute the efficiency of transmission. I assume the answers are suppose to be numbers between 1 and 0.

-First of all, how do we get an efficiency figure (regardless of degree of efficiency)? Is it the actual time it takes for transmission divided by the time it should take with no collisions?

-Second, I just want to clarify that when finding these highest and lowest efficiency values the assumption is that in each case exactly one collision occurs. So the dependent variable is the location of the collision?

Or....am I completely on the wrong track?

if the speed in bits of a packet transmission changes, does the distance in bits then change? this seems to be the crux of the question in 3b.

Jen,

You have the formula for efficiency upside down. You want to divide the time it would take with no collisions by the actual time. Otherwise the result will be bigger than one.

The assumption is that exactly one collision occurs. So, the TWO variables are how far apart the station are and when one starts to transmit relative to the other.

Tom

Paul,

Definitely. The distance light can travel in the time it takes to send a bit certainly changes if the time it takes to send a bit changes. Changing the transmission rate is the same as changing the time it takes to send a bit.

Tom

Can we assume in number 3 that the computers know how far apart they are from each other? In other words, would the maximum efficiency approach 1 as the distance between A and B approached 0. Thus, the time to detect the collision and then the time to realize the network is clear would be 0 b/c each machine "knew" where it was in relation to the other. Alternatively, do we assume they don't know this so that even if collision detection is immediate, A still has to wait the amount of time for 1 bit of data to travel the network to realize it (the network) is idle?

You can not assume that the computers know how far apart they are. On the other hand, they don't need to have some fixed time they wait. A machine connected to the network can sense whether a message is going by on the network wire. So, it can tell as soon as the network becomes idle (or busy) and change its behavior.

Tom