what is the differnce between on call/perdiem and full time position ?

When you work on call/per diem, you don't work unless an employer needs you, and you get paid for that day only. There is no guarantee or expectation of a set number of hours per week or month, and no benefits like insurance.

In a perfect world, you might work when you want to and turn down work when you don't, and earn enough money to buy your own insurance. You'd cover some long-term vacancies while someone is home with their new baby or gravely ill family member, as well as be the go-to person to cover scheduled vacations.

But this ain't no perfect world. Lots of on call people find they work crazy hours when things are difficult and then may not work for weeks.

A full time position has you working a set number of hours per week, whether you're needed or not. (The employer's assumption is that you will be needed, and that during any slow times you find ways to keep busy that perform some useful task.) Full time jobs are the only ones with benefits.

Full time is guaranteed hours of work in a rotation. For the nurses at my work it is 3 days on, 2 days off for full time. For part time it’s 2 days on 3 days off. And then you have the casual nurses who work only when called...they work all the time.