SCO (synchronous connection orientated) links

Key facts:

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.