Optimized Link State Routing Protocol for Ad Hoc Networks

1. Optimized Link State Routing Protocol for Ad Hoc Networks Qamar Abbas Tarar “Mobile ad-hoc networks based on wireless LAN” OLSR Protocol

2. Problems in MANETs • Scalability • QoS • Security • Interoperation with the Internet • Limited Battery Life • Node Mobility • Unreliable radio channelHidden terminal problem • Route maintenace • Unpredictable link properties OLSR Protocol

3. Classification of Routing Protocols for MANETS Unicast-Routing Protocol for MANET (Topology-based) CBRP Table-Driven/ Proactive Hybrid On-Demand-driven/Reactive Clusterbased/ Hierarchical Distance- Vector Link- State ZRP DSR AODV TORA LANMAR CEDAR DSDV OLSR TBRPF FSR STAR MANET: Mobile Ad hoc Network (IETF working group) OLSR Protocol

4. Proactive vs Reactive Routing Protocols • Proactive Routing Protocols (DSDV, OLSR) • + Routes to all reachable nodes in the network available. • + Minimal initial delay for application. • - Larger signalling traffic and power consumption. • Reactive Routing Protocols (DSR, CBR etc) • + Smaller signalling traffic and power consumption. • - A long delay for application when no route to the destination available OLSR Protocol

5. Structure OLSR • Overview • Multipoint relays • Neighbor sensing • MPR selection • MPR information declaration • Routing table calculation • Extensions in OLSR • Conclusions OLSR Protocol

6. Overview • OLSR • Developed by IETF • Table driven • Inherits Stability of • Link-state protocol • Selective Flooding • Periodic Link State • Information generated only by MPR • MPRs employed for optimization OLSR Protocol

7. Link State Routing (eg, OSPF) Retransmission node • Each node periodically floods status of its links • Each node re-broadcasts link state information received from its neighbour • Each node keeps track of link state information received from other nodes • Each node uses above information to determine next hope to each destination 24 retransmissions to diffuse a message up to 3 hops OLSR Protocol

8. OLSR Overview • In LSR • protocol a lot of control messages unnecessary duplicated • In OLSR • only MPRretransmit control messages: • Reduce size of control message; • Minimize flooding • Other advantages (the same as for LSR): • As stable as LSR protocol; • Proactive protocol(routes already known); • Does not depend upon any central entity; • Tolerates loss of control messages; • Supports nodes mobility. • Good for dense network OLSR Protocol

9. Optimized Link state routing (OLSR) 11 retransmission to diffuse a message up to 3 hops 24 retransmissions to diffuse a message up to 3 hops Retransmission node Retransmission node OLSR Protocol

10. Description of OLSR S P M Z X Y B A D • MPR (Multipoint relays) • MPR selector • Symmetric 1-hop neighbours • Symmetric strict 2-hop neighbours OLSR Protocol

11. Neighbor sensing • Each node periodically broadcasts Hello message: • List of neighbors with bi-directional link • List of other known neighbors. • Hello messages permit each node to learn topology up to 2 hops • Based on Hello messages each node selects its set of MPR’s OLSR Protocol

12. Example of neighbor table Two-hop neighbors One-hop neighbors Also every entry in the table has a timestamp, after which the entry in not valid OLSR Protocol

13. Multipoint Relays (MPR) • Reduce re-transmission in the same region • Each node select a set of MPR Selectors • MPR Selectors of node N - MPR(N) • - one-hop neighbors of N N OLSR Protocol

14. Multipoint Relays (MPR) • Reduce re-transmission in the same region • Each node select a set of MPR Selectors • MPR Selectors of node N - MPR(N) • - one-hop neighbors of N • MPR set of Node N • Set of MPR’s is able to transmit to all two-hop neighbors • Link between node and it’s MPR is bidirectional. N OLSR Protocol

15. Multipoint Relays (MPR) • Every node keeps a table of routes to all known destination through its MPR nodes • Every node periodically broadcasts list of its MPR Selectors (instead of the whole list of neighbors). • Upon receipt of MPR information each node recalculates and updates routes to each known destination OLSR Protocol

16. MRP selection in OLSR Node1 Hop Neighbors2 Hop NeighborsMPR(s) BA,C,F,GD,E C • Available BW • OLSR: node B will select C as its MPR So all the other nodes know that they can reach B via C 10 5 10 3 60 40 25 • D->B route is D-C-B, whose bottleneck BW is 3 110 50 100 30 OLSR Protocol

17. MRP selection in OLSR Node1 Hop Neighbors2 Hop NeighborsMPR(s) BA,C,F,GD,E C • Available BW • OLSR: node B will select C as its MPR So all the other nodes know that they can reach B via C 10 5 10 3 60 40 25 • D->B route is D-C-B, whose bottleneck BW is 3 110 50 100 • Optimal route (i.e., path with maximum bottleneck bandwidth: D-F-B (bottleneck bandwidth of 10) 30 OLSR Protocol

18. Multi-Point Relays/routers Passes Topology Information Acts as router between hosts Minimizes information retransmission Forms a routing backbone OLSR Protocol

19. Structure of an OLSR Network • MPRs form routing backbone • Other nodes act as “hosts” OLSR Protocol

20. Structure of an OLSR Network • MPRs form routing backbone • Other nodes act as “hosts” • As devices move OLSR Protocol

21. Structure of an OLSR Network • MPRs form routing backbone • Other nodes act as “hosts” • As devices move • Topological relationships change • Routes change • Backbone shape and composition changes OLSR Protocol

22. MPR information declaration • TC – Topology control message: • Sent periodically. Message might not be sent if there are no updates and sent earlier if there are updates • Contains: • MPR Selector Table • Sequence number • Each node maintains a Topology Table based on TC messages • Routing Tables are calculated based on Topology tables OLSR Protocol

23. Topology Table MPR Selector in the received TC message Last-hop node to the destination. Originator of TC message OLSR Protocol

24. Topology Table (cont) • Upon receipt of TC message: • If there exist some entry to the same destination with higher Sequence Number, the TC message is ignored • If there exist some entry to the same destination with lower Sequence Number, the topology entry is removed and the new one is recorded • If the entry is the same as in TC message, the holding time of this entry is refreshed • If there are no corresponding entry – the new entry is recorded OLSR Protocol

25. Routing Table • Each node maintains a routing table to all known destinations in the network • Routing table is calculated from Topological Table, taking the connected pairs • Routing table: • Destination address • Next Hop address • Distance • Routing Table is recalculated after every change in neighborhood table or in topological table OLSR Protocol

26. Extensions in OLSR • Qos OLSR • Fast OLSR • Towards IPv6 OLSR • Power saver mode • Change in the contents of TC packet OLSR Protocol

27. QoS Routing: Difficulties in QoS routing Due to mobility • Availability and manageability of Link state metrics • Link quality changes quickly and continuously • Computational cost and protocol overhead affect theperformance of the QoS routing protocol • Protocol performance evaluation is complex OLSR Protocol

28. Proactive QoS Routing • Advantages • suitable for the unpredictable nature of Ad-Hoc networks • suitable for the requirement of quick reaction to QoS demands • makes call admission control possible • avoids the waste of network resources • Disadvantages • introduces additional protocol overhead • trade-off between the QoS performance and traditional protocol • performance • But.. • Little work has been done to analyse the impact of the additional • overhead on pro-active QoS routing OLSR Protocol

29. QoS Versions of OLSR 10 5 60 40 25 110 50 100 30 • OLSR protocol does not guarantee to find the best bandwidth route • 3 heuristics are proposed to enhance OLSR in bandwidth aspect • The heuristics select good bandwidth neighbour as MPR 3 10 OLSR Protocol

30. QoS Versions of OLSR 3 10 10 5 60 40 25 110 50 100 30 • OLSR_R1: similar to OLSR (i.e., choose 1-hop neighbours that cover max. number of 2-hop neighbours), tie-breaker now max BW Node 1 Hop Neighbors 2 Hop Neighbors MPR(s) B A,C,F,G D,E C • OLSR_R2: select the best BW neighbors as MPRs until all the 2-hop neighbors are covered. Node 1 Hop Neighbors 2 Hop Neighbors MPR(s) B A,C,F,G D,E F • OLSR_R3: selects the MPRs in a way such that all the 2-hop neighbors have the max. bottleneck BW path through the MPRs to the current node. Node 1 Hop Neighbors 2 Hop Neighbors MPR(s) B A,C,F,G D,E A,F OLSR Protocol

31. Evaluation of QoS OLSR • Simulation: generate networks, run OLSR algorithms, compare results • against paths calculated by Link-State algorithm (i.e. complete • knowledge, all-pair shortest path) • Network area: 1000 M  1000 M • Number of nodes: 100 • Transmission range: 100 M, 200 M, 300 M • Bandwidth: assigned randomly • Results are averaged over 100 randomly generated networks OLSR Protocol

32. Performance Metrics Error rate:percentage of routes with non-optimal bandwidth Average difference: for routes with non-optimal bandwidth, how far off the optimal bandwidth are we Overhead: the average number of control messages transmitted per node MPR count: average number of MPRs in the network OLSR Protocol

33. Algorithm Transmission  Range Performace Cost Experimental Results Error Rate Average difference Over-head MPR Count StandardOLSR 300M 28% 46% 12 65 200 M 41% 51% 24 68 100 M 12% 45% 5 42 OLSR_R1 300 M 14% 22% 12 65 200 M 21% 26% 24 68 100 M 8% 44% 5 42 OLSR_R2 300 M 0% 0% 18 70 200 M 0% 0% 33 72 100 M 0% 0% 5.7 45 OLSR_R3 300 M 0% 0% 26 71 200 M 0% 0% 38 73 100 M 0% 0% 5.7 44 Pure Link State Algorithm 300 M 0% 0% 1245 100 200 M 0% 0% 979 100 100 M 0% 0% 28 100 OLSR Protocol

34. Fast OLSR • Due to Proactive nature,routes available when needed • However • In dense network, due to fast node Mobility, links valid only for short time period. • Hence to minize packet loss, • broken links between node and its neighbors must be quickly detected. OLSR Protocol

35. Neighbor Discovery in Fast OLSR • 3-procedures: • Switch to Fast-Moving/Default mode: In Fast mode,send Fast-Hellos and vice versa. A Fast-Hello is smaller than a Hello • Establishing fast Links: A node in Fast-Moving mode sends Fast-Hello messages at high frequency. • Refresh Fast links & Detect new broken links: by sending periodic Fast-Hellos OLSR Protocol

36. Towards IPv6 OLSR • OLSR operate well with both IPv4 and IPv6 • To operate with IPv6, the only required change • isto replace the IPv4 addresses with IPv6 address. • The minimum packet and message sizes should be adjusted accordingly, consideringthe greater size of IPv6 addresses. OLSR Protocol

37. Power saver mode • A node can indicate if it agrees to keep the packets of its neighbors • Any node, who wants to go in sleep mode, will select ONLY that neighbor as MPR who can keep its packets • TC packet will diffuse this info, and all data packets will be routed through that “power saver” node OLSR Protocol

38. Change in the contents of TC packet • Instead of advertising its set of MPRs, a node will list its neighbors who has selected him as an MPR • Many nodes (loosely connected, or at the boundaries) will not be selected MPR any node. So they will not send any TC (25% less overhead) • Less frequent changes in this set OLSR Protocol

39. Conclusions • Advantages • Route immediately available • Reactivity to topological changes can be adjusted by setting the time interval for HELLO messages • Minimize flooding by using MPR • Can be integrated into existing system as it requires no change to IP format • Disadvantages • Bigger overhead • Need more power • Not all allgoritms pubically documented • Needs more operational experience to debug OLSR Protocol

40. Readings • G. Pei, M. Gerla, and X. Hong, " LANMAR: Landmark Routing for Large Scale Wireless Ad Hoc Networks with Group Mobility," In Proceedings of IEEE/ACM MobiHOC 2000, Boston, MA, Aug. 2000. • R. Ogier, F. Templin, M. Lewis, " Topology Dissemination Based on Reverse-Path Forwarding (TBRPF) ," IETF Internet Draft , July 28 2003. • Thomas Clausen, Philippe Jacquet, " Optimized Link State Routing Protocol (OLSR) ," IETF Internet Draft , July 3 2003. • X. Hong, K. Xu, and M. Gerla, " Scalable Routing Protocols for Mobile Ad Hoc Networks " IEEE Network Magazine, July-Aug, 2002, pp. 11-21 • Thomas Kunz,Ying Ge, Louise Lamont, “ Quality of Service Routing in Ad-Hoc Networks Using OLSR” Carleton University, CRC,2002 • M Benzaid, P Minet and K A Agha, “Integrating fast mobility in the OLSR routing protocol” INRIA, LRI, France,September 2002. OLSR Protocol

41. Q & A OLSR Protocol