docs: def validate_network_topology(network_id,**kwargs):
      """
          Check for the presence of orphan nodes in a network.
      """
  
      user_id = kwargs.get('user_id')
      try:
          net_i = db.DBSession.query(Network).filter(Network.id == network_id).one()
          net_i.check_write_permission(user_id=user_id)
      except NoResultFound:
          raise ResourceNotFoundError("Network %s not found"%(network_id))
  
      nodes = []
      for node_i in net_i.nodes:
          if node_i.status == 'A':
              nodes.append(node_i.node_id)
  
      link_nodes = []
      for link_i in net_i.links:
          if link_i.status != 'A':
              continue
          if link_i.node_1_id not in link_nodes:
              link_nodes.append(link_i.node_1_id)
  
          if link_i.node_2_id not in link_nodes:
              link_nodes.append(link_i.node_2_id)
  
      nodes = set(nodes)
      link_nodes = set(link_nodes)
  
      isolated_nodes = nodes - link_nodes
  
      return isolated_nodes