Default: {4}           Value: Bit-set

    Set of protocol classes that can be negotiated for use on a
    transport connection. If the value of the network service
    attribute is CLNS, the class must be a subset of the classes
    supported by the OSI transport attribute clns classes supported.
    If the value is CONS, the classes must be a subset of the
    classes supported by the OSI transport attribute cons classes
    supported. If the value of the network service attribute is ANY,
    the classes must be a subset of the combined classes in the clns
    classes supported and cons classes supported attributes.

    set  [node node-id] osi transport template template-id -
         classes {class[,class...]}

    Example:

    set osi transport template osit$loop_cons  classes {0,2,4}