class Edge implements Serializable, Comparable<Edge> {

  @Override
  public String toString() {
    return "<"
        + getTail().getHostname()
        + ":"
        + getTail().getInterface()
        + ", "
        + getHead().getHostname()
        + ":"
        + getHead().getInterface()
        + ">";
  }

  public  Edge(NodeInterfacePair tail, NodeInterfacePair head);
  public  Edge(Interface tail, Interface head);

}