Ports and Links can often be augmented with these properties:

* name -- a human readable name for the port or link
* encoding -- the 'layer' of the port or link
* label -- the channel identifier of the port or link
* capacity -- the maximum data flow that can be transport through the port or over the link
* MTU -- the maximum transfer unit (thus packet size excluding headers) of a frame or packet
* (for links only) latency -- the one-way delay

Proposal: NML base will define name, encoding and label, but no other properties.