SQL how to question

Hi,

I was thinking I could do this with an OLAP function, but there's a
particularity that has me stumped

How can I get from this :
Client A Order x
Client A Order z
Client A Order a
Client B Order g
Client B Order h
Client B Order i
Client B Order l
Client B Order p
Client B Order m

To this:
Client A Order x 1 1
Client A Order z 1 2
Client A Order a 1 3
Client B Order g 2 1
Client B Order h 2 2
Client B Order i 2 3
Client B Order l 2 4
Client B Order p 2 5
Client B Order m 3 1

A dossier n° is assigned to each client and a line number to each order.
If there are more than 5 orders, a new dossier is created.