Attribute Protocol(ATT) 실시간 시스템 연구실 서재희

Contents ATT Attribute Attribute Protocol Methods

ATT Discovering attributes Reading the attributes Bluetooth Radio (also called Physical Layer) Link Layer L2CAP Attribute Protocol(ATT) Generic Attribute Profile(GATT) Generic Access Profile(GAP) GATT Based Profiles Security Manager(SM) Host Controller Interface(HCI) Discovering attributes Reading the attributes Writing the attributes Client Server model Attribute : data

Attribute Attribute Type Attribute Handle Access Permissions Attribute Value Attribute Structure Attribute Handle(2 octets) Attribute Type (2 octets or 16 octets) Attribute Value (Fixed or Variable length) Attribute Permissions (Established by GATT profile)

Attribute Type Attribute Type is identified by a Universally Unique Identifier(UUID). 128bit : Bluetooth SIG has defined a single 128-bit UUID, called Bluetooth Base UUID Ex) 00000000-0000-1000-8000-0085F9B34FB 16bit : In general. 128-bit UUID = 16-bit UUID * 2^96 + Bluetooth_Base_UUID Ex) 0x2A01 => full 128-bit UUID : 00002A01-0000-1000-8000-0085F9B34FB Service UUIDs : 0x1800 ~ 0x26FF Units : 0x2700 ~ 0x27FF Attribute Types : 0x2800~0x28FF Characteristic Descriptors : 0x2900~0x29FF Characteristic Types : 0x2A00~0x2AFF

Attribute Handle Attribute Handle is used by the client in all operations with the server to identify the attribute. Unique 0x0000 is reserved, and shall not be used. 0xFFFF is known as the maximum.

Attribute Permissions Each attribute has a set of permissions associated with it which determines the level of access that is permitted for that particular attribute. Access Permissions : Readable, Writable, Readable and Writable Authentication Permissions : clients to access attribute, server has to send notification or indication Authorization Permissions : client needs to be authorized before accessing an attribute value Error code is returned. Read Not Permitted Write Not Permitted Insufficient Authentication Insufficient Authorization Insufficient Encryption Key Size Insufficient Encryption

Attribute Value Fixed Length / Variable Length ATT does not allow multiple attribute values to be transmitted in a single PDU. A PDU contains only one attribute value and if the attribute value is too long to transmit in a single PDU, it can be split across multiple PDUs.

The Others Control Point Attributes Grouping of Attribute Handles Be written, notified, or indicated : control the behavior of a device Grouping of Attribute Handles The clients can request the first and the last handle associated with the group of attributes. Read By Group Type Atomic Operations Multiple clients may be connected to a server. The server treats each operation from the client as an atomic operation which is not impacted by any other client initiating an operation at the same time. Prepare Write Request, Execute Write Request

Attribute Protocol Role : Attribute Server, Attribute Client Request Response Client Server Indication Confirmation Client Server Command Client Server Notification

PDU(Protocol Data Unit) Format Security Opcode (1 octect) Attribute Parameters (Variable Length) Authentication signature (Optioanl – 12 octets) Method (6-bit) Command Flag (1-bit) Auth Signature Flag

Methods : Request and Response Type Message Request Parameters Response Parameters Error Opcode in Error, Handle in Error, Error Code Exchange MTU Client Rx MTU Server Rx MTU Find Information Starting Handle, Ending Handle (Handle, Type) Find By Type Value Starting Handle, Ending Handle, Type, Value (Found Handle, End Group Handle) Read By Type Starting Handle, Ending Handle, Type Length, (Handle, Value) Read Handle Value Read Blob Handle, Offset Part Value Read Multiple (Handle)* (Value) Read By Group Type Starting Handle, Ending Handle, Group Type (Handle, End Group Handle, Value) Write Handle, Value - Prepare Write Execute Write Flags

Methods : Command Type PDU Command Parameters Write Command Handle, Value Signed Write Command Handle, Value, Authentication Signature

Methods : Notification Type PDU Notification Parameters Handle Value Notification Handle, Value

Methods : Indication and Confirmation Type PDU Indication Parameters Confirmation Parameters Handle Value Indication Handle, Value

Bluetooth Analyze : BPA600 CC2540 Type, Value Message Request Parameters Response Parameters Error Opcode in Error, Handle in Error, Error Code Find By Type Value Starting Handle, Ending Handle, Type, Value (Found Handle, End Group Handle) Read By Type Starting Handle, Ending Handle, Type Length, (Handle, Value) Read Handle Value Write Handle, Value -

Bluetooth Analyze : BPA600 (Cont.) Read, Write Write Command Handle Value Notification Handle Value Indication