The Calling Extension facility. This
contains one of the following:
A sequence of hex digits with the value to
be put in the facility. These digits will be
converted to binary by the agent and put in
the facility. These octets do not include
the length octet.
A value containing the three character DEF
for a circuit means use the PLE default,
(the entry for the PLE default parameters
may not use the value DEF).
A zero length string indicates no facility
requested.