How to calculate Contention Ratio

Question

I am managing network for a college which provides shared internet access to students and employees. I have been asked to find the contention ratio for the internet provided. Is it the ratio of users sharing the connection?

Answer 1

A contention ratio is how much bandwidth you have versus how much you have sold.

For example, you might have a 1000Mbps internet link, but you have have 24x 100Mbps connections on it. That gives a contention of (24*100):1000, or 2.4:1.

Another scenario might be that you have an imposed bandwidth limit of 10Mbps per authenticated user, and you have 500 users. Then your contention ratio is (500*10):1000, or 5:1

This might be OK, because the chances of over 10 users using the entire of their 100Mbps at any given time might be slim (or it might not be), so you might still utilise less than the full 1000Mbps even with a contention ratio of 2:1.

A contention ratio of 1:1 (or lower) means that every single user you have sold bandwidth to is guaranteed a full connection speed at any given moment.

To figure out your contention ratio, you basically have to find out how much bandwidth you have available, and then figure out the maximum amount of bandwidth you have "sold".