The ACL link is a point-to-multipoint link between the master and all slaves participating on the piconet. It is considered a packet-switched connection primarily intended for transmitting non-time sensitive information, like data.
The SCO link is a point-to-point link between the master and a single slave. It is considered a circuit-switched connection primarily intended for transmitting time sensitive information, like voice.
The eSCO is the user extended synchronous data logical link. EV packets are used on the synchronous eSCO logical transport. The packets include a CRC and retransmission may be applied if no acknowledgement of proper reception is received within the retransmission window. eSCO packets may be routed to the synchronous I/O port. Three eSCO packet types (EV3, EV4, EV5) are defined for Basic Rate operation and four additional eSCO packet types (2-EV3, 3-EV3, 2-EV5, 3-EV5) for Enhanced Data Rate operation. The eSCO packets may be used for 64kb/s speech transmission as well as transparent data at 64kb/s and other rates.