Packet  Cost

Both  distance vector and link  state  routing  are lowest  algorithms. Tow factors  govern  how  cost is applied to packets  in determines  a route.

Cost  is applied  only by  routers  and not by  any other  stations on a network. Remember the link  from router  to the next  is a network  not a  point to point  cable. In many  topologies  every stations  on the  network example  of every packet that phase. If cost  was added  by every  station. Instead of by routers  alone. It would  accumulate  unpredictably ( the  number of station in a network  can change for a variety of reasons  many of them predictable.

Cost is applied  as a packet  leaves  the router  rather than as it enters. Most  networks  are broadcast network. When  a packet  is in the network  every station including  the router  can  pick it up therefore were  cannot  assign  any cost  to a packet  when it goes form  a network  to a router.

                                                                            figure cost in link state routing