A scatternet is an ad hoc network formed between two or more piconets (independent Bluetooth networks made up of one parent device and up to seven active child devices) in proximity. A scatternet allows its constituent devices to communicate with others that are not in their vicinity by having some devices act as “bridges” between piconets.
Due to the limitations of Bluetooth, scatternets do not have many practical applications today. However, researchers are exploring the future possibilities of scatternets for ad hoc communications between devices and robots.
In the past, “parent” devices in piconets were referred to as “master” devices, while “child” devices were called “slave” devices. These terms are very controversial today, with many experts preferring to adopt alternate terms to describe the relationship. Nevertheless, you may encounter this terminology while browsing old research, guides, and articles.
How a scatternet works
- Individual piconets are formed, each having a parent device and a set of active child devices. The piconet operates on a specific frequency-hopping pattern and timing controlled by the parent. Parent devices manage the communication in their piconet, with child devices following their instructions.
- Devices on different piconets scan for other Bluetooth-enabled devices within their range using inquiry procedures (a process known as device discovery).
- Upon discovery, the device wanting to connect sends a paging request to the target. If it receives a positive response, the device establishes a connection for communications.
- Some devices in each piconet are designated as “bridges“ to relay data between piconets. These devices play the role of a parent in one piconet and a child in another. Since each piconet operates on its own frequency-hopping pattern, the bridges must synchronize the hopping patterns of the piconets they connect.
- When a device in one piconet wants to send data to a device in another piconet, it sends the data to the bridge device, which then relays the data to the destination device in the other piconet.