最終更新:2022-08-15 (月) 13:46:51 (613d)
Bluetooth Classic/ベースバンド/アクセスコード
- Every packet starts with an access code.
- If a packet header follows, the access code is 72 bits long, otherwise the access code is 68 bits long and is known as a shortened access code.
アクセスコードの種類
- In the Bluetooth system all transmissions over the physical channel begin with an access code. Three different access codes are defined,
- All access codes are derived from the LAP of a device address or an inquiry address.
Bluetooth Classic/DAC? (Device Access Code)
- used during Page, Page Scan, Central Response, and Peripheral Response substates and shall be derived from the paged device’s BD_ADDR.
Bluetooth Classic/CAC (Channel Access Code)
- used in the Connection state, Synchronization Train substate, and Synchronization Scan substate, and forms the beginning of all packets exchanged on the piconet physical channel.
- The channel access code shall be derived from the LAP of the Central’s BD_ADDR.
Bluetooth Classic/IAC? (Inquiry Access Code)
- shall be used in the Inquiry substate.
- There is one general IAC (GIAC) for general inquiry operations and there are 63 dedicated IACs (DIACs) for dedicated inquiry operations.
使うLAPの種類
LAP アクセスコード長 Bluetooth Classic/CAC Central 72 Bluetooth Classic/DAC? Paged device 68/72 Bluetooth Classic/GIAC? (general IAC) Reserved 68/72 Bluetooth Classic/DIAC? (dedicated IAC) Dedicated 68/72 - When used as self-contained messages without a header, the DAC and IAC do not include the trailer bits and are of length 68 bits.
構造
ビット 4 64 4 フィールド プリアンブル Sync Word トレイラー(オプション)
プリアンブル
- 4ビット
- 後続のSync wordのLSBによって0101か1010
Bluetooth Classic/ベースバンド/Sync word?
- 64-bit code word derived from a 24 bit address (LAP);
- for the CAC the Central’s LAP is used
- for the GIAC and the DIAC, reserved, dedicated LAPs are used
- for the DAC, the Peripheral LAP is used.
- The sync words are based on a (64,30) expurgated block code with an overlay (bit-wise XOR) of a 64 bit full length pseudo-random noise (PN) sequence.
トレイラー
- Sync wordのあとにつく (主にCACの場合)
- Sync wordのMSBによって0101か1010
