This attribute specifies the encapsulation method to use when
exchanging protocol data units (PDUs) over this channel. IP and
Null protocolEncTypes are as defined in RFC1356.
NscNull is an encapsulation method for carrying IP datagrams
which requires removing 3 padding octets of zeroes and the
protocol identifier H.CC from the front of each data packet received
from the link in order to obtain the PDU. PDUs sent to the link are
propounded by a the protocol identifier H.CC. NscNull should only
be set when the remote host is following this same encapsulation
method.