NML has currently a one-to-one relation between the layer encoding (a URI to define the layer of sublayer of a specific 
Port of Link) and the label type (a URI to define the resource label of a technology).

Proposal: (was: Option 4). Use "encoding" for layer encoding and "labeltype" for label type

 <nml:Port id="....">
    <nml:encoding>http://schemas.ogf.org/nml/2013/10/ethernet#802.3</nml:encoding>;
    <nml:label labeltype="http://schemas.ogf.org/nml/2013/10/ethernet#vlan">1780</nml:label>
 </nml:Port>