The data rate of each ds0 in this bundle.
rate56 - 56kb/s
rate64 - 64kb/s
For ds0's on a T1 line, the value should be
rate56(1) if 'robbed bit' signaling is used,
and rate64(2) if clear channel signaling is
used.
For ds0's on a E1 line, the value should always
be rate64(2).
The value can be set only when the entry is
created.