Determines the number of bits and their bit positions
within the time-slot. 64k selection uses all 8 bits in
the time-slot. The two 56k selections use 7 of the 8
bits in the time-slot. 56k_MSB does not use the most
significant bit and 56k_LSB does not use the least
significant bit in the time-slot. If
the logical line is configured for DS0-A operation, rate
adaptions of 9.6 Kbps and 19.2 Kbps may be configured.