In Figure 2.6, the event number which is fixed is in increments of 1
In Figure 2.6, the time between occurrence of events is non-deterministic
Now what is of relevance to us is the distribution of . In order to obtain the distribution of we should note the following. In case it means that no events occur in the time interval and has exponential distribution with a mean value of .
Now to find the distribution of , this gives us:
Hence , are i.i.d exponential random variables with mean
. In order to obtain the distribution of 
it means that no events occur in the time interval 
and 
has exponential distribution with a mean value of 
.
this gives us:
are i.i.d exponential random variables with mean 
