Service desk id and portal id

Hi!

I was hoping that someone could shed some light regarding service desk and portal and how they are connected. We’ve seen that in most cases the service desk id and portal id are the same, but we’ve also encountered some customers who have different service desk id and portal id.

I am guessing these two are connected through the project id or am I mistaken? How would I be able to create a scenario where the service desk id and portal id are not the same value? So for example I would have service desk 10 and corresponding portal id would be 15?

Thanks in advance!