Indicates the current Rate Adaption in use. This may differ from the
configured Rate Adaption in ISDN PRI applications. This attribute indicates
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.