code: def add_link(self, link_id=None, dump=True):
          
          if link_id and link_id in self._links:
              return self._links[link_id]
          link = UDPLink(self, link_id=link_id)
          self._links[link.id] = link
          if dump:
              self.dump()
          return link
docs: Create a link. By default the link is empty
  
          :param dump: Dump topology to disk