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Computer Networks

Learn about the concepts of routing and forwarding in computer networks, including routing algorithms, virtual circuits, and connectionless forwarding. Understand the duties and responsibilities of the network layer, such as handling network resources, addressing, and multiplexing.

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Computer Networks

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  1. Computer Networks Bhushan Trivedi, Director, MCA Programme, at the GLS Institute of Computer Technology, Ahmadabad

  2. Chapter 7 The Network Layer

  3. Routing and Forwarding Routing is to know about other routers where each of them is located which networks they are connected to Forwarding is finding out about one’s own neighbouring routers forward a specified packet to its nearest neighbour to make it reach to a given destination

  4. Routing and forwarding Routing table contains information about nearest router for given destination Routing algorithms decide placement of routers Virtual circuit is mechanism used for connection oriented forwarding Datagrams are units of data sent in connectionless forwarding

  5. Network layer duties Handling accounting for usage of network resources Devise and implement mechanisms of identifying each machine uniquely Implement connectionless or connection-oriented forwarding Multiplexing and demultiplexing the transport layer and the data link layer jobs

  6. Two different types of routing Collection of networks organized by a single party is known as an autonomous system (AS) Exterior routing is across AS BGP (Border Gateway Protocol) Interior routing is within AS Distance Vector Link state AODV

  7. Other duties Accounting Receive Service from the Data Link Layer Provide Service to the Transport Layer

  8. Provide Service to DLL

  9. Provide service to transport layer

  10. Global Machine-Level Addressing Classful addressing The dotted decimal notation Classless addressing Aggregating multiple routing entries Unique address requirement Network Address Translation The real solution, IPv6

  11. Aggregating multiple route entries

  12. Routing table without aggregation

  13. Routing table after aggregation

  14. Unique address requirement

  15. Multiplexing and Demultiplexing Multiplexing and demultiplexing multiple transport layer connections Multiplexing and De-multiplexing the data link layer connections

  16. Forwarding Connection-oriented forwarding using virtual Circuits Connectionless forwarding using datagrams Connection-oriented vs. Connectionless Forwarding forwarding examples

  17. Steps involved in CO forwarding Find out a complete path to the other end Informs the routers along the path and gets their confirmation The service may be degraded or another path is tried if some router is not willing

  18. Steps involved in CO forwardingIntermediaries are to (a) reserve resources (b) set the priorities (c) take a call on other services needed (d) reserve an amount of bandwidth

  19. Steps involved in CO forwarding Connection ID is provided Independent of other routers No provision for a central authority The central authority needs to be consulted for every connection establishment process If the central authority fails, no connection is possile Assigning the connection number locally is simple and effective similar confirmation from the receiver is sought

  20. Forwarding Virtual circuit switching Multi protocol Label Switching Flow label in IPV6

  21. Forwarding Datagram based connectionless forwarding Comparison between Connection-oriented and Connectionless Forwarding

  22. Forwarding: Datagram based connectionless forwarding Not wasteful Autonomy and recovery Better fault tolerance

  23. Normal Path when no fault

  24. A router out of order

  25. A communication line out of order

  26. CO vs CL forwarding Connection establishment  VC requires this phase, Datagram-based solutions do not Routing Datagrams are checked and processed at every router while not in VC Speed of operation more time to route datagrams Congestion control Admission control vs routing around the congested path

  27. Avoiding congested path while routing

  28. CO vs CL forwarding Addressing Datagrams are designed to re-route Robustness Datagrams are more robust when congestions are expected Quality of service Connection-oriented service is better to provide QOS

  29. D is working

  30. D is not working

  31. B’s routing table before and after D stopped functioning

  32. Requirements of a good Routing Algorithms Simple enough to be implemented Should not oscillate Fault tolerance Speed Dynamism and flexibility Performance

  33. Issues in router’s performance A router must scale up to the size of the network attached to it Quality of service Delay delay tolerance bandwidth, particularly for real-time applications Fault tolerance High availability

  34. Router architecture

  35. Functions of a router: Lookup • Why addresses should be truncated by prefixes • Router should divide the addresses in as many groups as the number of interfaces available. • Easy management of the entries

  36. Address prefixes help in routing

  37. Issues in router’s performance Switching Queuing Robustness

  38. Robustness of a routing algorithm

  39. Routing Internal and External routing algorithms Distance Vector Routing Problem with count-to-infinity The split horizon hack Link State Routing Routing in MANet

  40. The subnet for routing and J sender

  41. Partial Routing table for J

  42. Facts related to Routing In a large network, there may be more than one path to a given destination Based on the parameter considered, a path can score better than others When we consider a different parameter, the best path may change

  43. Constructing routing tablesEstimated delay from I

  44. Constructing routing tablesEstimated delay from G

  45. Constructing routing tablesEstimated delay from C

  46. Constructing routing tablesAnother Example

  47. Constructing routing tablesAnother Example

  48. Constructing routing tables constructing routing table from two of the neighbor’s inputs

  49. Count to infinity problemE’s routing table when D goes down

  50. Count to Infinity ProblemAnother example

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