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The Network Layer

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The Network Layer

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  1. The Network Layer Chapter 5 Tanenbaum Chapter 5 Network

  2. Network Layer Design Isues • Store-and-Forward Packet Switching • Services Provided to the Transport Layer • Implementation of Connectionless Service • Implementation of Connection-Oriented Service • Comparison of Virtual-Circuit and Datagram Subnets Tanenbaum Chapter 5 Network

  3. Store-and-Forward Packet Switching fig 5-1 The environment of the network layer protocols. Tanenbaum Chapter 5 Network

  4. Implementation of Connectionless Service Routing within a diagram subnet. Tanenbaum Chapter 5 Network

  5. Implementation of Connection-Oriented Service Routing within a virtual-circuit subnet. Tanenbaum Chapter 5 Network

  6. Comparison of Virtual-Circuit and Datagram Subnets 5-4 Tanenbaum Chapter 5 Network

  7. Routing Algorithms • The Optimality Principle • Shortest Path Routing • Flooding • Distance Vector Routing • Link State Routing • Hierarchical Routing • Broadcast Routing • Multicast Routing • Routing for Mobile Hosts • Routing in Ad Hoc Networks Tanenbaum Chapter 5 Network

  8. Routing Algorithms (2) Conflict between fairness and optimality. Tanenbaum Chapter 5 Network

  9. The Optimality Principle (a) A subnet. (b) A sink tree for router B. Tanenbaum Chapter 5 Network

  10. Shortest Path Routing The first 5 steps used in computing the shortest path from A to D. The arrows indicate the working node. Tanenbaum Chapter 5 Network

  11. Flooding 5-8 top Dijkstra's algorithm to compute the shortest path through a graph. Tanenbaum Chapter 5 Network

  12. Flooding (2) 5-8 bottom Dijkstra's algorithm to compute the shortest path through a graph. Tanenbaum Chapter 5 Network

  13. Distance Vector Routing (a) A subnet. (b) Input from A, I, H, K, and the new routing table for J. Tanenbaum Chapter 5 Network

  14. Distance Vector Routing (2) The count-to-infinity problem. Tanenbaum Chapter 5 Network

  15. Link State Routing Each router must do the following: • Discover its neighbors, learn their network address. • Measure the delay or cost to each of its neighbors. • Construct a packet telling all it has just learned. • Send this packet to all other routers. • Compute the shortest path to every other router. Tanenbaum Chapter 5 Network

  16. Learning about the Neighbors (a) Nine routers and a LAN. (b) A graph model of (a). Tanenbaum Chapter 5 Network

  17. Measuring Line Cost A subnet in which the East and West parts are connected by two lines. Tanenbaum Chapter 5 Network

  18. Building Link State Packets (a) A subnet. (b) The link state packets for this subnet. Tanenbaum Chapter 5 Network

  19. Distributing the Link State Packets The packet buffer for router B in the previous slide (Fig. 5-13). Tanenbaum Chapter 5 Network

  20. Oscillation in Shortest Path Routing From “Data Network” by Bertsekas/Gallager Example 1. Consider the 16-node network shown in Fig. 5.25, where node 16 is the only desti­nation. Let the traffic input (in data units/sec) at each node i = 1, ... , 7, 9, ... ,15 be one unit and let the traffic input of node 8 be  > 0, where  is very small. Assume that the length of link (i, j) is dij = Fij where Fij is the arrival rate at the link counting input and relayed traffic. Suppose that all nodes compute their shortest path to the destination every T seconds using as link lengths the arrival rates Fij during the preceding T seconds, and route all their traffic along that path for the next T seconds. Assume that we start with nodes 1 through 7 routing clockwise and nodes 8 through 15 routing counterclock­wise. This is a rather good routing, balancing the traffic input between the two directions. Tanenbaum Chapter 5 Network

  21. Oscillation in Shortest Path Routing Figure 5.26 Oscillations in a ring network for link lengths dij equal to the link arrival rates Fij. Each node sends one unit of input traffic to the destination except for the middle node 8, which sends  > 0, where  < is very small. The numbers next to the links are the link rates in each of the two directions. As an example of the shortest path calculations, at the first iteration the middle node 8 computes the length of the clockwise path as 28(= 0 + 1 + 2 + ... + 7), and the length of the counterclockwise path as 28+8 (=  + 1+e+2+e+...+7+e), and switches its traffic to the shortest (clockwise) path at the 2nd routing. The corresponding numbers for node 9 are 28 and 28 + 7 , so node 9 also switches its traffic to the clockwise path. All other nodes find that the path used at the first routing is shortest, and therefore they do not switch their traffic to the other path. Tanenbaum Chapter 5 Network

  22. Oscillation in Shortest Path Routing Figure 5.26 shows the link rates corresponding to the initial and subsequent shortest path routings. Thus, after three shortest path updates, the algorithm is locked into an oscillatory pattern whereby all traffic swings from the clockwise to the counterclockwise direction and back at alternate updates. This is certainly the worst type of routing performance that could occur. Tanenbaum Chapter 5 Network

  23. Hierarchical Routing Hierarchical routing. Tanenbaum Chapter 5 Network

  24. Broadcast Routing Reverse path forwarding. (a) A subnet. (b) a Sink tree. (c) The tree built by reverse path forwarding. Tanenbaum Chapter 5 Network

  25. Multicast Routing (a) A network. (b) A spanning tree for the leftmost router. (c) A multicast tree for group 1. (d) A multicast tree for group 2. Tanenbaum Chapter 5 Network

  26. Routing for Mobile Hosts A WAN to which LANs, MANs, and wireless cells are attached. Tanenbaum Chapter 5 Network

  27. Routing for Mobile Hosts (2) Packet routing for mobile users. Tanenbaum Chapter 5 Network

  28. Routing in Ad Hoc Networks Possibilities when the routers are mobile: • Military vehicles on battlefield. • No infrastructure. • A fleet of ships at sea. • All moving all the time • Emergency works at earthquake . • The infrastructure destroyed. • A gathering of people with notebook computers. • In an area lacking 802.11. Tanenbaum Chapter 5 Network

  29. Route Discovery • (a) Range of A's broadcast. • (b) After B and D have received A's broadcast. • (c) After C, F, and G have received A's broadcast. • (d) After E, H, and I have received A's broadcast. Shaded nodes are new recipients. Arrows show possible reverse routes. Tanenbaum Chapter 5 Network

  30. Route Discovery (2) Format of a ROUTE REQUEST packet. Tanenbaum Chapter 5 Network

  31. Route Discovery (3) Format of a ROUTE REPLY packet. Tanenbaum Chapter 5 Network

  32. Route Maintenance (a) D's routing table before G goes down. (b) The graph after G has gone down. Tanenbaum Chapter 5 Network

  33. Node Lookup in Peer-to-Peer Networks (a) A set of 32 node identifiers arranged in a circle. The shaded ones correspond to actual machines. The arcs show the fingers from nodes 1, 4, and 12. The labels on the arcs are the table indices. (b) Examples of the finger tables. Tanenbaum Chapter 5 Network

  34. Congestion Control Algorithms • General Principles of Congestion Control • Congestion Prevention Policies • Congestion Control in Virtual-Circuit Subnets • Congestion Control in Datagram Subnets • Load Shedding • Jitter Control Tanenbaum Chapter 5 Network

  35. Congestion When too much traffic is offered, congestion sets in and performance degrades sharply. Tanenbaum Chapter 5 Network

  36. General Principles of Congestion Control • Monitor the system . • detect when and where congestion occurs. • Pass information to where action can be taken. • Adjust system operation to correct the problem. Tanenbaum Chapter 5 Network

  37. Congestion Prevention Policies 5-26 Policies that affect congestion. Tanenbaum Chapter 5 Network

  38. Congestion Control in Virtual-Circuit Subnets (a) A congested subnet. (b) A redrawn subnet, eliminates congestion and a virtual circuit from A to B. Tanenbaum Chapter 5 Network

  39. Hop-by-Hop Choke Packets (a) A choke packet that affects only the source. (b) A choke packet that affects each hop it passes through. Tanenbaum Chapter 5 Network

  40. Jitter Control (a) High jitter. (b) Low jitter. Tanenbaum Chapter 5 Network

  41. Quality of Service • Requirements • Techniques for Achieving Good Quality of Service • Integrated Services • Differentiated Services • Label Switching and MPLS Tanenbaum Chapter 5 Network

  42. Requirements 5-30 How stringent the quality-of-service requirements are. Tanenbaum Chapter 5 Network

  43. Buffering Smoothing the output stream by buffering packets. Tanenbaum Chapter 5 Network

  44. The Leaky Bucket Algorithm (a) A leaky bucket with water. (b) a leaky bucket with packets. Tanenbaum Chapter 5 Network

  45. The Leaky Bucket Algorithm (a) Input to a leaky bucket. (b) Output from a leaky bucket. Output from a token bucket with capacities of (c) 250 KB, (d) 500 KB, (e) 750 KB, (f) Output from a 500KB token bucket feeding a 10-MB/sec leaky bucket. Tanenbaum Chapter 5 Network

  46. The Token Bucket Algorithm 5-34 (a) Before. (b) After. Tanenbaum Chapter 5 Network

  47. Admission Control 5-34 An example of flow specification. Tanenbaum Chapter 5 Network

  48. Packet Scheduling (a) A router with five packets queued for line O. (b) Finishing times for the five packets. Tanenbaum Chapter 5 Network

  49. RSVP-The ReSerVation Protocol (a) A network, (b) The multicast spanning tree for host 1. (c) The multicast spanning tree for host 2. Tanenbaum Chapter 5 Network

  50. RSVP-The ReSerVation Protocol (2) (a) Host 3 requests a channel to host 1. (b) Host 3 then requests a second channel, to host 2. (c) Host 5 requests a channel to host 1. Tanenbaum Chapter 5 Network