April 2014
Beginner to intermediate
180 pages
4h 42m
English
Content preview from Getting Started with Bluetooth Low EnergyBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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Chapter 4. GATT (Services and Characteristics)
The Generic Attribute Profile (GATT) establishes in detail how to exchange all profile and user data over a BLE connection. In contrast with GAP (Chapter 3), which defines the low-level interactions with devices, GATT deals only with actual data transfer procedures and formats.
GATT also provides the reference framework for all GATT-based profiles (discussed in SIG-defined GATT-based profiles), which cover precise use cases and ensure interoperability between devices from different vendors. All standard BLE profiles are therefore based on GATT and must comply with it to operate correctly. This makes GATT a key section of the BLE specification, because every single item of data relevant to applications and users must be formatted, packed, and sent according to its rules.
GATT uses the Attribute Protocol (detailed in Attribute Protocol (ATT)) as its transport protocol to exchange data between devices. This data is organized hierarchically in sections called services, which group conceptually related pieces of user data called characteristics. This determines many fundamental aspects of GATT discussed in this chapter.
Roles
As with any other protocol or profile in the Bluetooth specification, GATT starts by defining the roles that interacting devices can adopt:
- Client
- The GATT client corresponds to the ATT client discussed in Attribute Protocol (ATT). It sends requests to a server and receives responses (and server-initiated updates) from ...
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