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

1SCO 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.
2SCO 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.
3SCO 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.
4A 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.
5The focus is minimization of time latency.
The main objective is to maintain data integrity rather than time latency.
6The 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.
7Packet retransmissions are not allowed, for assuring real-time transfer of voice traffic.
Packet retransmissions are allowed to ensure data integrity.
8Forward Error Correction (FEC) is applied for data reliability.
Both FEC as well as Backward Error Correction with retransmissions are adopted for data reliability.

Updated on: 11-Sep-2020

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