Page "Bluetooth" Paragraph 12

At any given time, data can be transferred between the master and one other device ( except for the little-used broadcast mode ).

The master chooses which slave device to address ; typically, it switches rapidly from one device to another in a round-robin fashion.

Since it is the master that chooses which slave to address, whereas a slave is ( in theory ) supposed to listen in each receive slot, being a master is a lighter burden than being a slave.

Being a master of seven slaves is possible ; being a slave of more than one master is difficult.

The specification is vague as to required behaviour in scatternets.