The Bluetooth Frame Structure

The Bluetooth network technology connects mobile devices wirelessly using short-wavelength, ultra-high frequency (UHF) radio waves over a short range to form a personal area network (PAN). Data is transferred between the Bluetooth devices as data frames. Two basic frame formats are defined, for transmitting data at basic data rate and for transmitting data at enhanced data rate.

Bluetooth Frame Format with Basic Data Rate

A Bluetooth frame with basic rate has three parts, access code, header and data as shown in the following diagram−

The various fields are−

  • Access Code− A 72-bit field containing synchronization bits to identify the master.

  • Header− A 54-bit field containing 18-bit patterns repeated thrice, having the following subfields−

    • Address− A 3 bit-field that can identify a maximum of seven slaves numbered 1 to 7. An address 0 depicts broadcast.

    • Type− A 4-bit field that identifies the type of data from upper layers. It identifies whether the frame is ACL, SCO, poll or null.

    • F− A bit for flow control. When the device cannot receive more frames, F is set to 1.

    • A− A bit for acknowledgement, for piggybacking an ACK to the end of the frame.

    • S− A bit denoting sequence number of the frame for detect retransmission. Only a single bit suffices since stop and wait protocol is used.

    • Checksum− An 8-bit field containing checksum for error detection.

  • Data− A variable length field ranging from 0 to 2744 bits that contains data or control information from upper layers.

Bluetooth Frame Format with Enhanced Data Rate

The frame for enhanced data rate contains additionally a guard field and a trailer as shown in the following diagram−

The additional fields and changes in data field are−

  • Guard− A 16-bit field containing a synchronization pattern that enables to switch to higher data speed while transmitting the data field.

  • Trailer− A 2-bit field denoting end of the variable length data field.

  • Data− A variable length field ranging from 0 to 2744 bits that contains high volume payload from upper layers.

Updated on: 11-Sep-2020

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