最終更新:2022-08-15 (月) 13:46:51 (40d)  

Bluetooth Classic/ベースバンド/アクセスコード
Top / 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/CACCentral72
    Bluetooth Classic/DAC?Paged device68/72
    Bluetooth Classic/GIAC? (general IAC)Reserved68/72
    Bluetooth Classic/DIAC? (dedicated IAC)Dedicated68/72
  • 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4644
    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

関連