Traffic Flow
     ========================================================>    
       +------+       +------+       +------+       +------+
   ---<>  R1  <>-----<>  R2  <>-----<>  R3  <>-----<>  R4  <>---
       +------+       +------+       +------+       +------+
       .              .      .              .       .      .
       .              .      .              .       .      .
       .              <------>              <------->      .
       .          Node Packet Loss      Link Packet Loss   .
       .                                                   .
       <--------------------------------------------------->
                        End-to-End Packet Loss