Bluetooth Packet Format 및 Connection 절차

Packet Format 및 Advertising 방법

Preamble

• Receiver에서 Frequency 동기화
• Symbol timing estimation
• AGC(Automatic Gain Control)
• 10101010b, 01010101b로 구성
• Access Address의 LSB Address가 1이면 01010101b, 이외에는 모두 10101010b

Access Address

• Advertising Packet은 10001110100010011011111011010110b (0x8E89BED6)
• Data Packet은 두 Device의 Link layer connection에 따라서 변경

PDU

• Protocol Data Unit

CRC

• Cyclic Redundancy Check

Advertising Packet Size :

• Header : Advertising Header 1Byte, Payload Length 1 Byte
• Payload: Advertiser Address : 6Byte, Advertising Data : 0-31Byte

Data Packet Size :

• Header : Data Header 1Byte, Payload Length 1Byte
• Payload : L2CAP Length 2Byte, L2CAP CID 2Byte, Data 0-21Byte, MIC(Message Integrity Check) 3Byte
• Data Payload Size는 암호화 여부에 따라서 차이 발생
• 암호화를 진행하면 MIC를 포함, 암호화하지 않으면 MIC를 포함하지 않음
• 암호화하지 않는 경우 Data Payload size : 0-27Byte
• 암호화하는 경우 Data Payload size : 0-31Byte

Advertising 작동 방식

Advertising Interver예

• Advertising Interval Min : 20ms
• Advertising Interval Max : 80ms

Passive Scan : Central Device에서 Slave에서 보내는 기본 Advertising Packet을 수신하고 추가적인 정보를 요청 하지 않음.

Active Scan : Central Device에서 Slave에서 보내는 기본 Advertising Packet을 수신하고 추가적인 정보를 요청.

Advertisement packet 포함 정보

• Device 상태 정보 : Discoverability and connectability mode
• Advertiser Address
• TX Power level
• Support Service
• Application data

Scan Response packet 포함 정보

• Device name
• Support service(Profiles)

Advertising PDU 종류

• ADV_IND : connectable undirected advertising event
• ADV_DIRECT_IND : connectable directed advertising event
• ADV_NONCONN_IND : non-connectable undirected advertising event
• ADV_SCAN_IND : scannable undirected advertising event
• SCAN_REQ
• SCAN_RSP
• CONNECT_REQ

Data PDU 종류

• LL Data PDU
• LL Control PDU
  • LL_CONNECTION_UPDATE_REQ
  • LL_CHANNEL_MAP_REQ
  • LL_TERMINATE_IND
  • LL_ENC_REQ
  • LL_ENC_RSP
  • LL_START_ENC_REQ
  • LL_START_ENC_RSP
  • LL_UNKNOWN_RSP
  • LL_FEATURE_REQ
  • LL_FEATURE_RSP
  • LL_PAUSE_ENC_REQ
  • LL_PAUSE_ENC_RSP
  • LL_VERSION_IND
  • LL_REJECT_IND

Bluetooth Specification Version 4.0 Volume 6 Part B 2.4 참조

Connection Process

BLE Module 구매