This is the i'th ITU-T facility required for this direct call. Within
the provisioning system, the user specifies the facility code along
with the facility parameters. The facility is represented internally as
a hexadecimal string following the X.25 ITU-T representation for
facility data.
The user specifies the facility code when adding, changing or
deleting a facility. The upper two bits of the facility code indicate
the class of facility. From the class of the facility, one can derive the
number of bytes of facility data, as follows:
Class A - 1 byte of fax data
Class B - 2 bytes of fax data
Class C - 3 bytes of fax data
Class D - variable length of fax data.