This object contains the bit map of the available DS0
channel in the DS1.
The MSB (most significant bit) is DS0 channel number 1.
The missing bytes is default to a value of 0.
A 1-bit indicates the channel is available for
configuration and a 0-bit indicates it isn't.
The length of this object is either 3 octets (for T1)
or 4 octets (for E1).
The most significant bit is transmitted first.