paying tax in advance

I just had to cough up 4 grand to the ATO for the first quarter of this year tax in advance for my SMSF.

Presumably they will ask for three more payments in coming quarters.

Is this common practice for the ATO? Do self employed people get taxed this way as well?

Just wondering cos I have always paid tax in arrears in the past and tbh I'm not very happy selling shares at this point in the year to cover a future tax liability which at this stage doesn't exist as I think I'm in the red for this year so far.

I realise I'll get the money back at year end if my profits are less but that isn't the point I am being forced to sell when I don't want to to cover a profit I haven't even made.

Arrrrgggghhhhh :(