SCO (synchronous connection orientated) links

Key facts:

Following a request from either the master or slave device, the master may establish a SCO link to that device.
The master can support a maximum of three SCO links, which can be to the same or different slaves.
SCO links are symmetric: the master sends a SCO packet, then the slave sends a SCO packet in the following slot, so the data rate in each direction is the same.
SCO packets are always transmitted in defined time slots, at regular intervals (every 2, 4, or 6 slots).
SCO packets are always 1 slot in length.
SCO packets are not acknowledged.

SCO packets

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

0000 NULL 1 slot No payload. Used for acknowledgements or flow control.

0001 POLL 1 slot No payload. Used by the master to poll slaves. Requires acknowledgement.

0010 FHS 1 slot Frequency Hopping Sequence. Contains address, clock, etc. information

0011 DM1 1 slot Data, Medium rate. An ACL packet, which can interrupt the regular flow of SCO data.

0101 HV1 1 slot High quality Voice (1/3 rate FEC) 10 data bytes transmitted every 2 slots (data rate = 64,000 bit/sec)

0110 HV2 1 slot High quality Voice (2/3 rate FEC) 20 data bytes transmitted every 4 slots (data rate = 64,000 bit/sec)

0111 HV3 1 slot High quality Voice (no error correction) 30 data bytes transmitted every 6 slots (data rate = 64,000 bit/sec)

1000 DV 1 slot Combined Data/Voice. Can be transmitted in place of an HV1 packet.

The DV packet payload contains:

No error correction: 10 voice data bytes.

2/3 rate FEC: 1 payload header byte (as for an ACL packet);
0...9 data bytes;
2 CRC bytes.

0000	NULL	1 slot	No payload. Used for acknowledgements or flow control.
0001	POLL	1 slot	No payload. Used by the master to poll slaves. Requires acknowledgement.
0010	FHS	1 slot	Frequency Hopping Sequence. Contains address, clock, etc. information
0011	DM1	1 slot	Data, Medium rate. An ACL packet, which can interrupt the regular flow of SCO data.
0101	HV1	1 slot	High quality Voice	(1/3 rate FEC)	10 data bytes	transmitted every 2 slots (data rate = 64,000 bit/sec)
0110	HV2	1 slot	High quality Voice	(2/3 rate FEC)	20 data bytes	transmitted every 4 slots (data rate = 64,000 bit/sec)
0111	HV3	1 slot	High quality Voice	(no error correction)	30 data bytes	transmitted every 6 slots (data rate = 64,000 bit/sec)
1000	DV	1 slot	Combined Data/Voice. Can be transmitted in place of an HV1 packet.

No error correction:	10 voice data bytes.
2/3 rate FEC:	1 payload header byte (as for an ACL packet); 0...9 data bytes; 2 CRC bytes.