The document defines the Generic Attribute Profile (GATT) which specifies how data is exchanged over a Bluetooth Low Energy connection. GATT defines client and server roles, attributes containing user data identified by handles and types, and an attribute data hierarchy with characteristics and services. It provides an example of a GATT database view showing the arrangement of handles, types, permissions and values in a Bluetooth Low Energy connection.

1. BlueNRG GATT Database
Winfred LU
AMG GCSA
STMicroelectronics

2. • Generic Attribute Profile (GATT)
• defines how to exchange user data (attributes) over a BLE connection
• Roles
• Client
• sends requests to a server
• performs Service Discovery
to know server’s attributes
• Server
• responds to requests
• stores user data
Generic Attribute Profile (GATT)
Request
Response
Client Server

3. • Handle
• 16-bit unique identifier
• 0x0001 – 0xFFFF
• Type
• UUID (Universal unique Identifier)
• 128-bit globally unique
• 32/16-bit SIG adopted
• xxxxxxxx-0000-1000-8000-00805F9B34FB
• Permission
• access rights: readable, writable, notifiable,
indicatable
• security level required to access: encryption,
authorization
• Value
• actual data content
• with variable length
• in format according to type
Attribute structure
Handle Type Permission Value

4. database / profile • Attribute
• There are 3 types of Attributes
• Primary Service
• Secondary Service
• Characteristic
• Attributes are grouped into Services
• Service Definition
• Service Declaration
• 0 or more Characteristics
• Characteristic Definition
• Characteristic Declaration
• Characteristic Value
• 0 or more Descriptors
• Extended Properties Descriptor
• Client Characteristic Configuration Descriptor (CCCD)
• Characteristic User Description Descriptor
Attribute data hierarchy
Characteristic
…
Descriptor
Service
Characteristic
…
Descriptor
Characteristic
…
Descriptor
Service
Characteristic
…
Descriptor
Characteristic
…
Descriptor

5. ATT database view
5
Handle Type Permissions Value
1 0x2800 (GATT Primary Service) Read 0x1801 (Generic Attribute)
2 0x2803 (Characteristic Declaration) UUID=0x2A05, Handle=0x0003, Properties=0x20
3 0x2a05 (Service Changed) Indicate 0xFFFF0000
4 0x2902 (Client Characteristic Configuration) Read, Write 0x0000
5 0x2800 (GATT Primary Service) Read 0x1800 (Generic Access Profile)
6 0x2803 (Characteristic Declaration) UUID=0x2A00, Handle=0x0007, Properties=0x4E
7 0x2a00 (Device Name) Read, Write wo Rsp, Wrie, S-
Writes
0x74736574 --> “test”
8 0x2803 (Characteristic Declaration) UUID=0x2A01, Handle=0x0009, Properties=0x4E
9 0x2a01 (Appearance) Read, Write wo Rsp, Wrie, S-
Writes
0x0000
A 0x2803 (Characteristic Declaration) UUID=0x2A04, Handle=0x000B, Properties=0x02
B 0x2a04 (Peripheral Preferred Connection
Parameters)
Read 0xFFFF0000 FFFFFFFF

6. ATT database view in BlueNRG GUI
6
https://www.st.com/en/embedded-software/stsw-bnrgui.html

7. Handle Value
1 0x1801
2 0x2A05 0003 20
3 0xFFFF0000
4 0x0000
5 0x1800
6 0x2A00 0007 4E
7 0x74736574
8 0x2A01 0009 4E
9 0x0000
A 0x2A04 000B 02
B 0xFFFF0000 FFFFFFFF
ACI_GATT_Read_Handle_Value
7
Bits Field
7:0 0: Broadcast
1: Read
2: Write without Response
3: Write
4: Notify
5: Indicate
6: Authenticated Signed Writes
7: Extended Properties
23:8 Characteristic Value Handle
39:24 Characteristic UUID

8. • Bluetooth SIG
• Core Spec, Profiles, Assign Numbers
• https://www.bluetooth.com/specifications/specs/
• Intro to Bluetooth Generic Attribute Profile
• Mohammad Afaneh @ Ellisys
• https://www.bluetooth.com/bluetooth-resources/intro-to-bluetooth-gap-gatt/
• Introduction to Bluetooth Low Energy – GATT
• Kevin Townsend @ Adafruit
• https://learn.adafruit.com/introduction-to-bluetooth-low-energy/gatt
• Getting Started with Bluetooth Low Energy – GATT (Services and Characteristics)
• Kevin Townsend, Carles Cufí, Akiba, Robert Davidson
• https://www.oreilly.com/library/view/getting-started-with/9781491900550/ch04.html
References