eSCO (extended synchronous connection orientated) links

Key facts:

eSCO links were added in version 1.2 of the Bluetooth specification.
Following a request from either the master or slave device, the master may establish an eSCO link to that device.
eSCO packets are always transmitted in predetermined time slots: the regular interval between eSCO packets is specified when the link is established.
eSCO packets can be 1 or 3 slots in length.
eSCO packets to/from a specific slave are acknowledged, and may be retransmitted if not acknowledged.

eSCO packets

The packet type is determined by the TYPE code in the header:

0000 NULL No payload. Used for acknowledgements or flow control.

0001 POLL No payload. Used by the master to poll slaves. Requires acknowledgement.

0111 EV3 Extended Voice (no error correction), 1 slot: maximum 30 data bytes plus a 16-bit CRC.

1100 EV4 Extended Voice (2/3 rate FEC), 3 slots: maximum 120 data bytes plus a 16-bit CRC.

1101 EV5 Extended Voice (no error correction), 3 slots: maximum 180 data bytes plus a 16-bit CRC.

0000	NULL	No payload. Used for acknowledgements or flow control.
0001	POLL	No payload. Used by the master to poll slaves. Requires acknowledgement.
0111	EV3	Extended Voice (no error correction), 1 slot: maximum 30 data bytes plus a 16-bit CRC.
1100	EV4	Extended Voice (2/3 rate FEC), 3 slots: maximum 120 data bytes plus a 16-bit CRC.
1101	EV5	Extended Voice (no error correction), 3 slots: maximum 180 data bytes plus a 16-bit CRC.