1. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 1 The Network Layer

2. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 2 OSI Network Layer

3. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 3 TCP/IP Model Uses a subset of the OSI layers Session and Presentation layers not present

4. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 4 TCP/IP Model

5. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 5 Node Types Source node Intermediate node Destination node

6. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 6 Source Node Functions Receives packets from transport layer Moves packets from source to destination –typically through a chain of nodes –requires a route Passes packets to data link layer for eventual transmission

7. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 7 Intermediate Node Functions Receives packets from data link layer Routes packets from source to destination –typically through a chain of nodes –requires a route Passes packets back to data link layer for eventual retransmission to destination via selected route

8. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 8 Intermediate Node Layers

9. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 9 Routing Functions Interconnection of multiple networks Determines output line for incoming packet Path selection based on destination address and routing algorithm Alternates based on network status (link state)

10. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 10 Multiway Routing

11. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 11 Routing Algorithms Algorithms –flooding –shortest path distance vector routing link state routing –flow-based

12. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 12 Flooding Algorithm Incoming packets sent on all lines except incoming (many duplicate packets) Each packet has hop counter, initially set to expected path length Decremented each hop, discard pkt if zero First arriving packet took shortest path Puts a lot of extra traffic on network

13. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 13 Shortest Path Routing Network consists of nodes and arcs Arcs have costs assigned Routing occurs at nodes Routing should minimize total path cost –requires cost metric –requires computation

14. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 14 Route Computations Follows link state distribution to all routers Each router contains all link delays Shortest path to each router computed, using path cost as metric –frame delay cost –other cost factors (distance, traffic, equipment) Algorithm

15. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 15 Shortest Path Algorithm For each possible starting node –Put starting node in optimal list –Repeat Compute total costs to all new neighbors Assign lowest as optimal for that node Delete other possibilities for that node –Until each node has optimum assigned for given starting node End

16. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 16 Route Computation to Node A

17. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 17 Route Computation to Node A

18. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 18 Route Computation to Node A

19. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 19 One-Hop Costs to Node A

20. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 20 Route Computation to Node A

21. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 21 Belman-Ford Routing Distance vector method Uses shortest path algorithm Results in routing table for each node

22. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 22 Distance Vector Routing Each router has vector of optimal paths to each destination Tables updated by neighbor exchange Metrics (measurements) –hops (trace) –queue length (known internally) –delay (ping)

23. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 23 Link State Routing Routers learn neighbor addresses (“hello” packet sent at bootup) Cost or delay measured to each (measured by “echo” packets) State information distributed to all routers (“link state packet”) Shortest delay to all other routers computed

24. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 24 Network with Link State Delays

25. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 25 Routing Table at Node A

26. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 26 Network with Link State Delays

27. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 27 Link State Packets Each sends on all outgoing lines Duplicates and lower sequence numbers discarded Age decremented, packet discarded when zero

28. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 28 Maximal Flow in Network Ford-Fulkerson theorem Each link has known capacity in each direction Cuts made separating source from destination Maximal flow is capacity across cut having minimum capacity

29. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 29 Problem! Networks have many paths All possible cuts have to be examined Number of possible cuts can be VERY large

30. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 30 Algorithmic Solution Uses distance metric –hop count –delay –other calculates capacity sequentially avoids combinatorial problem

31. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 31 Maximum Flow Algorithm Expand from start node to adjacent nodes Expand by node layers until final node Subtract capacity of minimal link from path Repeat until no more capacity (cut) Capacity of network is capacity of cut Paths have minimal hop count

32. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 32 Maximal Flow Example Numbers shown are channel capacities

33. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 33 First Layer Branch

34. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 34 Second Layer Branch

35. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 35 Third Layer Branch

36. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 36 ABCD Capacity Reduced by 4

37. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 37 First Layer

38. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 38 Second Layer

39. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 39 Third Layer

40. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 40 AFKD Capacity Reduced by 2

41. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 41 First Layer

42. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 42 Second Layer

43. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 43 Third Layer

44. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 44 AFED Capacity Reduced by 2

45. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 45 First Layer

46. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 46 Second Layer

47. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 47 Third Layer

48. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 48 Fourth Layer

49. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 49 AGJCD Capacity Reduced by 2

50. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 50 First Layer

51. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 51 Second Layer

52. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 52 Third Layer

53. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 53 Fourth Layer

54. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 54 AFHKD Capacity Reduced by 2

55. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 55 First Layer

56. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 56 Second Layer

57. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 57 Third Layer

58. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 58 Fourth Layer

59. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 59 Fifth Layer

60. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 60 AFHJCD Capacity Reduced by 1

61. 6/12/2016© 2010 Raymond P. Jefferis IIILect 05 - 61 Minimal Cut (Capacity = 13)