DDS-PRI is full duplex 56k link, No framing in loop
data so loop speed is also 56k. Data stream:
--d1 d2 d3 d4 d5 d6 d7--
DDS-CC is full duplex 64k link. Does not require framing
bit but uses a same format as SC, ninth bit position is
lumped with primary channel and not used for control.
Loop speed is 72k, Primary channel rate is 64k.
--d1 d2 d3 d4 d5 d6 d7 F d8--