The objective is to solve the slab front separately from the rest of the façade. This is where all the complexity of the curtain wall is concentrated. Some of the most important issues to resolve are fire sectorization, total guarantee of the continuity of the horizontal division between spaces up to the façade, load transmission to the main structure and staking out.
Once this structure has been assembled, the rest of the façade can be closed with glass panes over two supports or by placing some mullions anchored at any point of the transoms. Both possibilities allow great design freedom to architects.
Due to the clarity of the approach, the fact of delimiting the area of greatest complexity of execution and the compositional freedom, this system is the one that is most used today.