A bit string that indicates the path types that are available
in the station.
The value initially takes the value 0, then for each type of
path that this node has available, 2 raised to a power is added
to the sum. The powers are according to the following table:
Path Power
---- -----
Primary 0
Secondary 1
Local 2
For example, a station having Primary and Local paths available
would have a value of 5 (2**0 + 2**2).