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CIS 725

CIS 725. Network Layer. Network Layer. This layer provides communication between any two nodes Uniform addressing scheme independent of the network technology. Network layer. Data Link layer. Problems to be addressed. Routing Congestion control. Routing. Processing nodes

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CIS 725

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  1. CIS 725 Network Layer

  2. Network Layer • This layer provides communication between any two nodes • Uniform addressing scheme independent of the network technology Network layer Data Link layer

  3. Problems to be addressed • Routing • Congestion control

  4. Routing • Processing nodes • Switches/routers • Communication links

  5. Datagram routing • Each packet is routed independently • Unordered • Unreliable

  6. Virtual Circuit routing • Set up a path for each connection • All messages are sent over this path • Ordered • Reliable

  7. Routing Table • Routing table contains the next hop information • At each node i, for each destination j, what is the next hop

  8. Distance Vector Algorithms Bellman-Ford Algorithm • Distance table: • Routing table distance from i to j via k

  9. Routing table • Protocol at node i: On receiving routing table from k update column k of the distance table as follows For each destination j, if k reports its distance to j as d then update Dj,k = d + weight(i,k)

  10. Recompute the routing table as follows: For each destination k, update next hop to j, where Dj,k = min(Dx,k: for all x)

  11. Periodically or whenever the routing table changes, send routing table to all neighbors

  12. Bellman-Ford Algorithm b c a c d a b e b c d e 2 a c d e 2 a b d e 4 4 1 1 b 2 d 2 2 2 a 1 1 b c d e b 2 a c d e a 2 a b d e 4 a 4 c 4 2 c e c 1 b 1 d 2 e 2

  13. Bellman-Ford Algorithm b c a c d a b e b c d e 2 a c d e 2 a b d e 4 3 4 1 3 5 1 b 2 d 4 6 2 3 2 2 a 1 1 b c d e b 2 a c d e a 2 a b d e b 3 4 b 3 2 c e c 1 b 1 b 4 b 3 d 2 e 2

  14. Bellman-Ford Algorithm • Distance vector algorithm • Best path criteria • Latency • Jitter • bandwidth

  15. Counting to infinity a 1  101 100 c b 1 a a c c a a a b b b a a a a c c a a a a a a a b b 100 100 4 2 4 2 101 101 1 5 3 3 1 5 3 b b b b b b b b b 3 3 3 1 1 1 1 1 1

  16. < a,b,c,d,e,f> 5 1 1 c 1 d 1 e 1 f a b 4 3 2 1 5 20 dest next dist path

  17. 5 1 1 c 1 d 1 e 1 f a b 4 3 2 1 5 b  c  d  e dest next dist Next to last hop b d e c f b b b b b 5 3 4 1 2 a c e d b

  18. Link State Routing • Each node maintains the state of every link • State of the link may contain several types of information

  19. Learning local information • Exchange hello packets periodically • Measure the cost of adjacent links

  20. Distributed link state information • Link state packet: * source id * cost of incident edges * sequence numbers

  21. Building Link State Packets (a) A subnet. (b) The link state packets for this subnet.

  22. Distribution Algorithm • Controlled flooding - hop count - sequence numbers - age

  23. Receive LSP from nbr j - compare sequence numbers - update topology table - propagate LSP to all nbrs except j

  24. Hierarchical Routing • Divide area into regions • Maintain accurate information about nodes in the same region

  25. Hierarchical Routing Hierarchical routing.

  26. Source-routing • Message contains the entire path • Routing table lookup is avoided at each node

  27. Broadcasting/Multicasting • To send a message to all nodes: - make a separate message to each destination - route each message independently

  28. Multi-destination routing • Include all destination address in message • Each node decides which links to forward so that it reaches all destinations

  29. Multicast trees • Create a spanning tree • Prune the spanning tree: Steiner tree

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