Two types of data links are defined by Bluetooth link layers−
Synchronous Connection Oriented (SCO) Link
Asynchronous Connection-Less (ACL) Link
SCO is a symmetric, point-to-point link between the master device and the slave device connected via Bluetooth.
ACL is a point – to – multipoint link for transmitting general data packets using Bluetooth connection. ACL is used for irregular traffic between a master device and one or more slave devices.
Differences between SCO and ACL
|1||SCO provides a circuit switched connection, where a dedicated, point-to-point link is established between the master device and the slave device before communication starts.||ACL is a packet oriented link, i.e. the link establishes a packet – switched network.|
|2||SCO is a symmetric link, i.e. fixed slots are allocated for each direction.||Both symmetric and asymmetric traffic are supported. The master device controls the bandwidth of the ACL link.|
|3||SCO radio links are used for time critical data transfer, mainly voice data.||ACL is used for transmission of data traffic which are delivered at irregular intervals.|
|4||A master device can support three SCO links with the same or different slaves. A slave device can have a maximum of three SCO links with its master device.||One master device which connects with maximum seven slave devices via ACL links to form a Piconet.|
|5||The focus is minimization of time latency.||The main objective is to maintain data integrity rather than time latency.|
|6||The maximum data rate of SCO link is 64,000 bps (bits per second).||The maximum data rates of ACL links can reach a 57.6 Kbps in downlink and 721 bps in uplink.|
|7||Packet retransmissions are not allowed, for assuring real-time transfer of voice traffic.||Packet retransmissions are allowed to ensure data integrity.|
|8||Forward Error Correction (FEC) is applied for data reliability.||Both FEC as well as Backward Error Correction with retransmissions are adopted for data reliability.|