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  • 1. Dissertation DefenseOn-Demand Link-State Routing in Ad-Hoc Networks Soumya Roy Computer Engineering, University Of California, Santa Cruz Adviser : Prof. JJ Garcia Luna Aceves
  • 2. Presentation Outline Wireless ad-hoc networks On-demand link-state routing protocol  Source-tree On-demand Adaptive Routing protocol (SOAR)  Path Selection  On-demand Link Vector Protocol (OLIVE) Node-centric hybrid routing approach for practical scenarios of ad-hoc networks
  • 3. PART ONE Wireless Ad Hoc Networks
  • 4. Wireless Ad Hoc Networks WLAN Ad hoc NetworksNodes acts as sources, relays and destinations of data packets Routing protocol is needed for data delivery
  • 5. Challenges in Designing Routing Protocols for Mobile Ad-Hoc Networks Significant Packet Loss :  Fading, interference, collisions Less bandwidth than wired networks Network Topology highly dynamic because of router or host mobility Routing protocols should adapt fast to link failures and converge fast Routing overhead should be minimal
  • 6. Taxonomy of Routing Protocols Proactive Routing (WRP, DSDV, OLSR, STAR)  Maintains routes for all destinations  Redundant routes Reactive Routing (AODV, DSR, DST)  Maintains routes for necessary nodes  Uses flooding of requests to discover paths  Long delays for path set up
  • 7. Main goal is to ….Explore how link-state information can be used efficiently for setting up on-demand routes
  • 8. Previous Work Proactive link-state protocols  Source Tree Adaptive Routing (STAR)  Exchanges source trees  Topology Broadcast based on Reverse-Path Forwarding (TBRPF)  Exchanges reportable part of source tree  Optimized Link-State Routing (OLSR)  Uses multipoint relays to prevent flooding Performance good compared to on-demand routing protocols using routing information in other forms
  • 9. PART TWO On-Demand Link- State Routing
  • 10. Outline Source Tree On-demand Adaptive Routing (SOAR) Challenges in the path selection On-demand Link Vector Routing (OLIVE)
  • 11. Source Tree On-demand Adaptive Routing (SOAR)
  • 12. What is Source Tree Each node can build source tree based on paths to all reachable destinations a b c SOAR exchanges minimal source trees d e f g h i j k l m Source Tree at node a
  • 13. What is a Minimal Source Tree Contains paths to important nodes (relays, potential relays, receivers) a a b b c c d e f d e f jj g jjg h i k Minimal Source Tree l m l reported by node a Source Tree at a
  • 14. Construction of Topology Table i x a a x i y c i c y + =Minimal source tree Minimal source tree Partial topology at i of x of a  Modified Bellman-Ford Algorithm used for path selection
  • 15. Summary Query, Reply for path discovery Updates for path repair ForcedUpdate, ForcedReply for forcing nodes adopt shortest paths Links validated using sequence number Data packets contain traversed paths
  • 16. Performance Evaluation (ns2) 20 nodes 1000mx300m rectangular field IEEE 802.11 MAC Link layer notification of link failures Re-routing of data packets possible in case of link breakage Comparisons with DSR and AODV
  • 17. Effect of Increasing Flows (pause=0s)
  • 18. Effect of Mobility (10 flows)
  • 19. Effect of Loading (10 flows)
  • 20. Challenges of Path Selection in On-demand Link State Routing
  • 21. Path Selection Algorithm Links advertised by b (c) (c) c d f Links advertised by c (c) (c) (c) a (b) (c) g (b) h (b) e b Path through a neighbor valid if later has advertised it Choose the shortest among the valid options
  • 22. Computing Source TreeOPT-TREE : Given a graph and a set oflabels corresponding to each link, whatis maximum size of the source tree thatcan be built while satisfying the rules ofshortest path and on-demand routeadvertisement?NP complete problem (reduction of3SAT problem to a graph)
  • 23. Computing Source Tree (contd…)
  • 24. Heuristic for Computing Source Tree A polynomial time approximation (O(nd^2)) algorithm Finding shortest valid paths for a destination and combining those paths Local maxima instead of global maxima Disadvantage: computing source tree not an efficient usage of routing information A mechanism for policy-based routing
  • 25. Computing source graph (in SOAR) MBF BF (a,d1) (x,d2) j d1 >d2 (x,d2) i i i k (a,d1+1)(x,inf) (x, d2+1) a x a x a xd1 d2 j (j,k) link has been j j advertised by x only k k kPartial topology at i Source Graph at i Advertised Source Tree at i
  • 26. How does SOAR handle pathselection problem Computes source graph Exchanges source trees Uses forced routing to convert source graphs to trees Disadvantage:  Loops can form  Extra overhead of forced routing
  • 27. Next Step ……. Use of complete path information Links in paths validated using sequence numbers Links merged to help in local route repair and limited route requests Instantaneous loops to be prevented without any control overhead in data packets or any global synchronization
  • 28. On-Demand Link Vector Protocol(OLIVE)
  • 29. Overview of OLIVE Route discovery  Setting up new paths  RREQ, RREP and RREPACK Route Repair  Locally repair routes or limit route searches  FRREQ, FRREP Route Failure Notification  To notify route failures  RERR, RERRACK
  • 30. Use of path information in OLIVE
  • 31. Use of path information (contd …) c e
  • 32. RREQ d a RR EQRREQi j k RR EQ c b RREQ RREPACK RREP a d RR EP RREP Example (Route Discovery)i j k RR RREPACK PE RR AC b K c EP RREP RREPACK
  • 33. Example (Route Error and Repair) j j d c d c RREQ FRREQ RREQ FRREP a b a b FR EQ RR FR RE RERRACK RR EQ RE P k RERR k Q i RREQ i
  • 34. Properties of OLIVE When cost of path can increase, inter- neighbor synchronization is used  Predecessors release the successor  Loop-free paths set up when all predecessors release Every node knows correctly at every instance its set of predecessors Data packets from unknown predecessors always dropped
  • 35. Performance Evaluation (ns2) 50 nodes 1500x300m (range = 250m) 2Mbps DSSS radio interface Random Waypoint model IEEE 802.11 Compared with DSR, OLSR, TBRPF, AODV
  • 36. Simulation Results (10 flows)Percentage Throughput Total Control Packets
  • 37. Simulation Results (10 flows)Optimality of routes End to end delay
  • 38. Effect of Packet Load (20 sources)Control packets sent Percentage Delivery
  • 39. Effect of Packet Load (20 sources)Optimality of routes End-to-end Delay
  • 40. Quantifying loopsPacket rate = 8 packets/s Packet rate = 10 packets/s
  • 41. Summary Elaborately studied the problem of using on-demand link-state information for routing Developed routing solutions that give better performance than existing popular routing protocols OLIVE can be very good choice for use in ad hoc networks
  • 42. PART 2Node-Centric Hybrid Routing for Ad Hoc Networks
  • 43. Outline Introduction Reasons behind node-centric hybrid routing Methods and new protocols Performance evaluation
  • 44. Introduction Practical scenarios for mobile ad-hoc networks will have traffic between mobile nodes and netmarks Where can we see such scenarios :  Internet Access Points  Hosts for DNS services  Web Proxies  Group leaders  Cluster-heads for hierarchical routing
  • 45. Practical Ad Hoc Networks
  • 46. Related Work in Hybrid Routing Zone Routing Protocol (Haas & Pearlman)  Proactive routing within zones  Reactive routing between zones Landmark Hierarchy (P.F. Tshuchiya)  Node centric approach to hierarchical routing for proactive routing  Landmark’s address: address for common node Our approach: Type of routing is based on nodes and not on zones or areas
  • 47. Why Node-centric Hybrid Routing On Demand path creation towards netmarks  Each session set up leads to flooding, delay  Intuitively not best approach if the netmark is communicated frequently though not continuously Maintaining pro-active routes  High control overhead  Redundant paths as peer-to-peer communication is much less compared to number of nodes Node-centric hybrid routing: a tradeoff  Proactive routes towards netmarks  On demand path creation among mobile nodes
  • 48. Methods of Node-Centric HybridRouting  Prolonged Caching  Caching of netmark information for long enough periods  Proactive routes  Proactive routing for the netmark so that paths towards netmarks remain always updated while paths between mobile nodes are set up on-demand
  • 49. Protocols with Prolonged Caching Route errors and route requests for netmarks do not depend on traffic AODV : longer routing entry timeout for netmarks DSR : advantage not realizable since routing solely controlled by traffic SOAR :Netmarks will be important for longer time interval, hence caches/maintains netmark path information for longer periods
  • 50. Protocols With Proactive Netmark Routes1. Nemarks advertise their presence  MAC layer sends beacons  Routing Layer sends Hellos2. Route errors and route requests for netmarks do not depend on traffic Changes 1 and 2 can be easily made for DSR, SOAR and AODV
  • 51. Protocols with Proactive Routes(contd…)3. New paths to netmarks are always advertised Change 3 needs modifications  SOAR sends updates immediately on discovering new routes  AODV and DSR need new type of control packets for proactive route set up
  • 52. SOAR with Hybrid Functionality SOAR performs better than both DSR or AODV Modifications of SOAR to incorporate hybrid routing simpler than in DSR or AODV Netmark Aware On Demand Link-State Routing (NOLR) : extended caching of netmarks Netmark-Enhanced Source Tree Routing (NEST) : proactive routes for netmarks
  • 53. Setting up paths in NEST  Forward paths are set up proactively Reverse paths are set up by traffic flows (soft state or on-demand) (e,b) hel (e,a) lo n n lo nhel b b b (e,d) update a a (e,c) a (e,c) update dupd (e,e) d d (e,e) at e c c c update e e e
  • 54. Issues in Hybrid Routing Forwarding of data packets  Use of subnet address for ad hoc networks Multiple Netmarks  Load balancing  Complexity in packet forwarding (static, dynamic, hybrid affiliations)  Asymmetry in paths  Change in query mechanism (anycast queries)
  • 55. Performance Evaluation Using ns2 Comparison of NEST, NOLR with DSR, AODV and SOAR
  • 56. Traffic and Mobility Models Mobility Model : random waypoint model Traffic Pattern  FLOW OFF/ON model  Data Traffic and Voice traffic Simulation
  • 57. Simulation Scenario 1 31 nodes single netmark in the centre of a rectangular field (1000m x 500m) size Range = 250m Simulation length : 600 secs load = 3 packets/sec 5 packets/sec Speed : 5m/s-20m/s
  • 58. Performance Evaluation (3 pkts/s) Percentage ThroughputControl packet
  • 59. Performance Evaluation (5 pkts/s)Control packets Percentage Throughput
  • 60. Simulation Scenario 2 31 nodes single netmark  Static  Mobile in a restricted region  Mobile throughout the rectangular field Traffic flows ( 2 models)  6 random flows among netmark and mobile nodes (battlefield or relief)  Any mobile node can talk to netmark (Internet)
  • 61. Performance Evaluation
  • 62. Simulation Scenario 3 31 nodes Two static netmarks To observe : can anycast route discovery lead to any significant improvement
  • 63. NEST A-SOAR NOLRPerformance Evaluation
  • 64. Contributions First detailed study on use of link-state information on-demand Developed two unique highly efficient routing protocols Demonstrated the complexity of path selection in on-demand routing Presented a new genre of hybrid routing targeting practical ad-hoc networks
  • 65. Future Work Opportunistic version of OLIVE to target practical ad-hoc networks Node-centric version targeting huge networks without added complexity of hierarchy management Modeling ad-hoc networks based on parameters like node density
  • 66. Acknowledgements Thanks to JJ for being the greatest adviser Thanks to Richard, Katia for being on my defense committee, and Suresh for being on my advancement committee. Thanks to my parents and brother who have always supported me Thanks to my friends in Baskin Engineering, Bay Area and CCRG for all the help during my PhD life
  • 67. THE END
  • 68. Publications SOAR (IEEE Infocom 2001) Heuristic for Source Tree Computation (ICCCN 2002) Node-Centric Hybrid Routing (Globecom 2002, Mascots 2002, Book Chapter) Path Selection problem (submitted to PODC 2003) OLIVE (Mobicom 2003)
  • 69. Pending publications
  • 70. Simulation Results (10 flows)Total Control Bytes Total MAC layer packets