Difference between ACL and SCO Link in Bluetooth

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

	SCO	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.