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Asynchronous connection-oriented logical transport

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Asynchronous connection-oriented logical transport (ACL) is a communications protocol used in the in the Bluetooth system. It is used as a transmission link used for data communication, and is formatted with an access code (72 bits) + packet header (54 bits) + payload + CRC (16 bits).

ACL is used when data integrity is more important than avoiding latency. In this type of link, if a payload encapsulated in the frame is corrupted, it is retransmitted. A secondary returns an ACL frame in the available odd-numbered slot if and only if the previous slot has been addressed to it. ACL can use one, three or more slots and can achieve a maximum data rate of 721 kbit/s.

Packet types

DM1, DH1, DM3, DH3, DM5, DH5, AUX1

D(1)(2)
(1) M : rate 2/3 FEC used
H : no FEC used

(2) 1 : 1 slot used for one frame
3 : 3 slots used for one frame
5 : 5 slots used for one frame