Asynchronous Connection-Less (ACL) Link

Bluetooth link layers define two types of data links, Asynchronous Connection-Less (ACL) Link, being one of them. It is the type of link used for transmission of general data packets using Bluetooth connection. ACL is a point – to – multipoint link used for irregular traffic between a master device and one or more slave devices.

Features of Bluetooth ACL links

  • ACL is a packet oriented link, i.e. the link establishes a packet – switched network.

  • ACL is used for transmission of data traffic which are delivered at irregular intervals, where maintaining data integrity is more important than the time latency.

  • Both symmetric and asymmetric traffic are supported. The master device controls the bandwidth of the ACL link. Slave devices poll in order to decide who will transmit data.

  • ACL links are point – to – multipoint in nature, i.e. there is one master device which connects with maximum seven slave devices to form a Piconet.

  • Broadcast messages are also supported by ACL links.

  • ACL links can reach a maximum data rates of 57.6 Kbps in downlink and 721 bps in uplink.

  • The packets are delivered on best – effort basis, i.e., no guarantees are given for data transmission. Lost frames may be retransmitted.

  • ACL has two frame types−

    • DM which provides Forward Error Correction (FEC)

    • DH which doesn’t provide FEC

  • In order to protect data packets, automatic retransmission query (ARQ) scheme is used.