The Generic Attributes (GATT) define a hierarchical data structure that is exposed to connected Bluetooth Low Energy (LE) devices.
GATT profiles enable extensive innovation while still maintaining full interoperability with other Bluetooth® devices. The profile describes a use case, roles and general behaviors based on the GATT functionality. Services are collections of characteristics and relationships to other services that encapsulate the behavior of part of a device. This also includes hierarchy of services, characteristics and attributes used in the attribute server.
GATT is built on top of the Attribute Protocol (ATT) (see Bluetooth Core System Architecture for block diagram and explanations), which uses GATT data to define the way that two Bluetooth Low Energy devices send and receive standard messages. Note that GATT is not used in Bluetooth BR/EDR implementations, which use only adopted profiles.
GATT Profile Hierarchy
The Generic Attribute Profile (GATT) procedures define standard ways that services, characteristics and their descriptors can be discovered and then used to allow Bluetooth Low Energy devices to transfer data. The profile describes a use case, roles and general behaviors based on GATT functionality.
The top level of the hierarchy is a profile, which is composed of one or more services necessary to fulfill a use case. A service is composed of characteristics or references to other services. A characteristic consists of a type (represented by a UUID), a value, a set of properties indicating the operations the characteristic supports and a set of permissions relating to security. It may also include one or more descriptors—metadata or configuration flags relating to the owning characteristic.
GATT groups these services to encapsulate the behavior of part of a device, and describes a use case, roles and general behaviors based on the GATT functionality. This framework defines procedures and formats of services and their characteristics, including discovering, reading, writing, notifying and indicating characteristics, as well as configuring the broadcast of characteristics.
Client and Server Roles
GATT defines client and server roles. GATT procedures can be considered to be split into three basic types: Discovery procedures, Client-initiated procedures and Server-initiated procedures. The GATT server stores the data transported over the ATT and accepts ATT requests, commands and confirmations from the GATT client. The GATT server sends responses to requests and sends indications and notifications asynchronously to the GATT client when specified events occur on the GATT server. GATT also specifies the format of data contained on the GATT server.
To see all the adopted GATT-based specifications, visit the GATT Specifications page.