This field is used to specify the Transport version to use when
 connecting to this node.  This must be either:

   TP4       - Use TP4 with the default DECnet T-Sel (DEC0)
   TP4=tsel  - Use TP4 with the specified T-Sel value
   NSP       - Use NSP

 If the N-Sel in the node address field is "20", this must be NSP.  If the
 N-Sel is any other value, this must be TP4.

 If using a T-Sel value other than "DEC0", it must be specified after an
 equals sign.  The T-Sel value must be an even number of hexadecimal
 digits (if an odd number of digits is supplied, a "0" is added to the
 end).