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.