# Is there any difference between inter-arrival time and interval time?

Hi

I am wondering some statistical books write inter-arrival time and other write interval time.
Is there any difference between them? if so, how can I calculate both?
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Commented:
Inter-arrival time is usually used to refer to the time between events.
Interval time is usually used to refer to the length of time you observe for events.

For example, if you are looking at calls to a datacenter and there are 10 calls per minute your inter-arrival time would be 6 minutes.

And if you looked at 1 hour intervals, the number of calls per interval would be 600.

I hope that helps.
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Commented:
So generally you pick the interval, and then inter-arrival time is just interval/count_of_events
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Author Commented:
Hi Tommy,

is the inerval like arrival rate ?
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Commented:
Interval is just a time period.
If you sample at 1 hour intervals, then that's your interval. 1 hour.

If that's not what you are talking about, perhaps you could point us to something that would help us understand how it is being defined in your case.
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Author Commented:
Tommy,

I have arrival time like the below:
10:30
10:32
11:02
11:25

for more than 3000 requests. I need to get lambda to calculate the Poisson distribution. can you help me how can get that ?
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Commented:
lambda is just the average time between events. So divide the number of events by the total time.

If you have a start and end time, use total_requests/(end_time - start_time)

If you just have the times, then use (total_requests-1)/(last_request_time - first_request_time)
You subtract 1 because you have no way of knowing (in this case) how long it took for the first event to happen.
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Author Commented:
Thanks you. it is so clear
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