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Bluetooth GATT vs ATT vs GAP: Differences Explained

By RF Wireless Expert Team

Based on the architecture and functional descriptions provided in the Bluetooth Core Specification, here is an explanation of GAP, ATT and GATT, followed by a comparison table highlighting their differences.

1. GAP (Generic Access Profile)

GAP is the foundational profile that dictates how Bluetooth devices interact with each other at a macro level. It is responsible for the “who you are,” “how you are found,” and “how you connect” aspects of Bluetooth communication.

Key Functions:

  • Device Discovery & Connections: It defines the modes and procedures for devices to discover each other (e.g., scanning and advertising), establish connections and manage security/authentication.

  • Roles: In Bluetooth Low Energy (LE), GAP defines four specific operational roles:

    • Broadcaster: Transmits advertising data but does not accept connections.
    • Observer: Scans for advertising data but does not initiate connections.
    • Peripheral: Advertises its presence and accepts a single connection from a Central device.
    • Central: Scans for devices and initiates multiple connections to Peripherals.

2. ATT (Attribute Protocol)

ATT is a lower level peer to peer protocol used to transfer simple, small pieces of data over a Bluetooth connection. It acts as the transport mechanism for data exchange.

Key Functions:

  • Attributes: It defines data as “attributes.” Each attribute is a small data value (usually just a few octets) that is self identifying using a Universally Unique Identifier (UUID).

  • Roles: It establishes a strict Client and Server relationship.

    • Server: Stores the attributes and accepts requests/commands.
    • Client: Sends commands and requests to read or write the attributes on the Server.

  • Operations: It provides the actual protocol methods for the Client to request data (Read/Write) and for the Server to send data asynchronously (Notifications/Indications).

3. GATT (Generic Attribute Profile)

GATT is a framework built directly on top of the Attribute Protocol (ATT). While ATT provides the “rules of transport” for data, GATT provides the “organizational structure” for that data.

Key Functions:

  • Data Hierarchy: It defines how the raw attributes from ATT are grouped and formatted into a strict, recognizable hierarchy:
    • Profiles: High level definitions of a use case (e.g. Heart Rate Profile).
    • Services: Collections of related data and behaviors to accomplish a specific function.
    • Characteristics: The actual data points within a service, consisting of a value, properties (how it can be accessed) and descriptors (metadata like user readable descriptions).
  • Interoperability: By enforcing this data structure, GATT ensures that a Client device knows exactly how to discover, traverse and understand the data hosted on a Server device, enabling seamless application level interoperability.

Summary Comparison Table

Feature / AspectGAP (Generic Access Profile)ATT (Attribute Protocol)GATT (Generic Attribute Profile)
Primary FocusDevice connections, discovery, and security.Data transport and protocol operations.Data organization, structure, and formatting.
What it Manages”How devices find each other and connect.""How data is physically moved back and forth.""What the data means and how it is grouped.”
Defined RolesCentral, Peripheral, Broadcaster, Observer (for BLE).Client (requests data), Server (holds data).Client (reads/writes data), Server (hosts services).
Key ConceptsAdvertising, Scanning, Paging, Link Establishment, Security Modes.Attributes, UUIDs, Opcodes, Read/Write requests, Notifications.Profiles, Services, Characteristics, Descriptors.
Position in StackTop-level control layer governing the overall device state and transport layers.Protocol layer sitting on top of L2CAP.Profile layer sitting directly on top of ATT.
Real-World AnalogyThe receptionist who introduces two people and checks their ID.The envelope and mail carrier that moves a letter between two people.The standardized forms and language used written inside the letter.

References & Further Reading

  1. Bluetooth SIG : Bluetooth Core Specification Version 6.3, May 5, 2026.
  2. Bluetooth SIG : Bluetooth Technology Overview

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