Understanding BLE Central and Peripheral Roles
The central and peripheral labels describe the connection roles in a BLE interaction, not the importance of either device.
What you’ll learn
- Describe what central and peripheral roles do
- Separate GAP roles from GATT client and server roles
- Distinguish a connectable peripheral from a broadcast-only beacon
Central: find and initiate
A central can scan for advertisers and initiate a connection to a connectable peripheral. A phone connecting to a fitness tracker is a familiar example. A BleuIO dongle configured in central role can also scan for nearby devices. The central role describes who initiates the connection, not which device is more important.
Peripheral: advertise and accept
A peripheral advertises to allow a central to establish a connection. A connectable sensor is a familiar example. A broadcast-only beacon instead uses the GAP broadcaster role: it advertises data but does not accept a connection. This distinction matters when a device appears in a scan but cannot be connected to.
GAP roles versus GATT roles
Central/peripheral are connection roles defined at the GAP level. GATT client/server describe who asks for attribute operations and who holds the attribute database. A central is often the GATT client and a peripheral often the server, but the concepts are separate. Some devices support more flexible combinations. GAP also defines an observer role for receiving broadcast data without connecting.
GAP answers “how do these devices find and connect?” GATT answers “how is application data organized and exchanged?”
Compare the roles
| GAP role | Typical behavior | Example |
|---|---|---|
| Central | Initiates a connection to a peripheral | Phone connecting to a tracker |
| Peripheral | Accepts a central’s connection | Connectable tracker |
| Broadcaster | Sends advertising data without accepting a connection | Broadcast-only beacon |
| Observer | Receives broadcasts without connecting | Listener collecting beacon data |
BleuIO’s AT+CENTRAL command places the dongle in central role for its AT+GAPSCAN scan. The advertising lesson uses those commands in a complete lab. For now, identify the roles in the phone-and-tracker example above.
Check your understanding
A beacon broadcasts an identifier but never accepts a connection. Which GAP role best describes it?
Key takeaways
- A central scans and can initiate connections.
- A peripheral advertises for a possible connection; a broadcaster sends data without accepting one.
- GAP connection roles and GATT data roles describe different layers.
Further Reading and Resources
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