There’s an in-depth paper by Nicole Todtenberg and Rolf Kraemer on A Survey on Bluetooth Multi-hop Networks. The paper describes the basics of Bluetooth and Bluetooth Mesh.
The paper goes on to describe connected networks (scatternets) and connectionless networks including some complex topics such as scatternet formation, topology maintenance, optimisation, inter-piconet scheduling and packet forwarding.
Read about Beacons and the Bluetooth Mesh