written 6.9 years ago by
modified 3.1 years ago
- Bluetooth packet can be of 1-slot (625 us) or 3-slot (1875 us) or 5-slot (3125 us).
Fig5. Bluetooth Packets
- Each packet consists of a 72 bit access code.
- The access code is used for packet identification.
- Every packet exchanged on the channel is preceded by its access code.
- Recipients on the piconet compare incoming signals with access code. If the two do not match, the received packet is not considered valid and rest of its contents are ignored.
- The 72 bit access code is derived from master identity.
- Thus, access code is also used for synchronization and compensating for offset.
- The access code is robust and resistant to interference.
Fig6. Packet Format in Bluetooth
- Header part of the packet is used by the Link Control (LC) logical channel. It has the following format:
Fig7. Header format
- AM_ADDR: temporary address assigned to active members of the piconet, used on all packets in both directions sent between the master and the addressed slave. An all-zero AM_ADDR is used to broadcast to all slaves.
- TYPE: type of packet. There are 12 types of packets for each SCO and ACL physical links, and four types of common control packets for both.
- FLOW: for flow control.
- ARQN: for ACK.
- SEQN: contains sequence number for packet ordering.
- HEC: header error check for header integrity.
- There can be two types of payload: voice and data. Synchronous connection oriented (SCO) packets only have voice field, while Asynchronous connection less (ACL) packets only have data field.