Increasing the Performance of MANETs

1. Increasing the Performance of MANETs Throughput and QoSPerformanceEnhancingMechanisms for Unicast and Group Communication in Proactive Mobile Ad Hoc Networks PhD Dissertation Erlend Larsen January 28th 2011 Erlend Larsen, PhDDissertation 2011

2. Outline • Introduction • Motivation • Challenges • OLSR • Thesisoverview • Contributions • Unicast routing • Group communication • Concludingremarks

3. Motivation Improving the information flow in emergency and rescue operations • Today • Mainlyone hop broadcastvoice, ”walkie-talkies” or TETRA withlow data capacity • Tomorrow • Voice • Situational awareness • Position sharing • Geographically mapped events • Access to maps and construction drawings • Etc. • But…

4. Challenges • Medium access: Contention-basedrandomaccess • Collisions • interference • Distributedrouting • Inconsistency, overhead • Node mobility • Node density • Partitioning or lowshareof medium access • Link quality • Varying • Result: Lowperformance, difficult to support QoS

5. Optimized Link State Routing – OLSR– a proactive routing protocol • Maintains a full topology overview • Maintains a ConnectedDominatingSet • Manyimplementationsavailable • Linux, Windows • NS-2 simulator • IETF’sproposedproactiveroutingprotocol for MANETs

6. OLSR – Control messages • HELLO messages with own neighborhood information periodically broadcasted to all neighbors • Type of link to all neighbors: asymmetrical, symmetrical, lost • MPR selection • Timeout information • TC messages • Global link information

7. MultiPointRelays in OLSR • A node selects a subset of its neighbors as MPRs, to reach all 2-hop neighbors • MPRs do: • TC generation • Forwarding

8. Overview of the work

9. Contributions to Unicast Routing

10. Rerouting Time and Queueing in Proactive Ad Hoc Networks Vinh Pham, Erlend Larsen, Knut Øvsthus, PaalEngelstad and Øivind Kure In proceedingsofthePerformance, Computing, and Communications Conference 2007 (IPCCC 2007), New Orleans, USA, April 11-13, 2007, pp. 160-169.

11. Motivation • Discovery: Rerouting due to mobility exceeds the expected 4-6 seconds. S D

12. The contributions • Analysis and simulationofthererouting time • Proposedsolutionofadaptingthenumberof MAC layerretries

13. A link break broken down Last successfull data transmission from A directly to C Link is broken between A and C. A’s queue is being filled up. Garbage packets are discarded from A’s queue New route established via B Last Hello from C received at A A transmits data to C B A C

14. Solution – Adaptive Retry Limit Node A’sInterfaceQueue Packet 7 is transmitted 1 time and discarded Packet 2 is transmitted 6 times and discarded Packet 1 is transmitted 7 times and discarded 9 8 9 8 7 7 7 1 8 2 9 9 8 2 3 3 In Out • Assumes: • Retry limit = 7 • All packet to the same destination

15. Results

16. Conclusion • Rerouting time is affected by: • Packetsize and rate • MAC layerqueuesize • MAC layerretries • Adaptingthe MAC layerretriesreducesthererouting time.

17. Gateways and Capacity in Ad Hoc Networks Erlend Larsen, Vinh Pham, PaalEngelstadand Øivind Kure In proceedingsofthe International ConferenceonAdvances in Human-oriented and PersonalizedMechanisms, Technologies, and Services 2008, (I-CENTRIC 2008), Sliema, Malta, October 26-31, 2008, pp. 390-399, ISBN: 978-0-7695-3371-1

18. Motivation • Gateways can interconnect ad hoc networks with external networks. • The gateway’s position in the ad hoc network may impact the capacity of the ad hoc network • Understanding the impact of gateway positions on the offered capacity can be valuable.

19. Investigated scenarios • One, two and multiple gateways • Trafficflowingeitherintothenetwork from thegateway to all ad hoc nodes, or vice versa. • Downlink • Uplink • With and withoutdynamicgatewayselection

20. One gateway downlink • Throughput is highest with the GW near the center. • At the center the average number of hops is the lowest. • Lack of route is the dominating cause of packet loss

21. Two gateways downlink • Throughput greatly increased compared to one gateway. • Throughput peak at 750 m separation – where the average number of hops is lowest. • The results make a jump at 550 m, i.e. when the two gateways no longer are in each other’s sensing range.

22. MAC layerretransmissions Centeredgatewayreceivesnetworktraffic (Uplink scenario) • Mobility leads to lower throughput in the downlink scenarios

23. Conclusions • The average hop count affects the capacity: • Additional GWs increase the throughput • No further throughput increase when all nodes are in 1-hop range of a GW. • The GWs’ sensing range affects the capacity: • Exposed node problem with downlink (from GW to ad hoc nodes) • Hidden node problem with uplink (to GW from ad hoc nodes) • Lower throughput for downlink traffic: • Mobility + MAC retransmissions • Without dynamic gateway selection, the performance of two gateways equals that of one gateway.

24. RoutingwithTransmission Buffer Zones in MANETs Erlend Larsen, Lars Landmark, Vinh Pham, Øivind Kure and PaalEngelstad In proceedingsofthe IEEE International Symposium on a World of Wireless Mobile and Multimedia Networks 2009 (WoWMoM 2009), Kos, Greece, June 15-18, 2009.

25. Motivation • Paper A: Rerouting due to mobility exceeds the expected 4-6 seconds. • Canweanticipate and reroute in advance? S D

26. Transmission buffer zones Buffer zone D S Safe zone

27. Results

28. Conclusions • The buffer zone solution improves the goodput over standard OLSR – eventhough loops appear more frequently. • The sizeofthe buffer zonecan be optimizeddependingon node mobility. • The node classification metric may be other than signal strength • MAC layerretries • Average link loss rate

29. Contributions to Group Communication

30. Preemption Mechanisms for Push-to-Talk in Ad Hoc Networks Erlend Larsen, Lars Landmark, Vinh Pham, Paal E. Engelstad and Øivind Kure Accepted at the 34th IEEE ConferenceonLocal Computer Networks 2009 (LCN 2009), Zürich, Switzerland, October 20-23

31. Motivation • Push-to-Talk (PTT) • should be supported in MANETs for emergency and crisis scenarios. • Distributed using multicast/efficient flooding. • Without priority, the PTT traffic will be severely impacted by background traffic.

32. The contributions • Investigatehow PTT traffic is affected by backgroundtraffic • Study theeffectofpriorityqueuing • Propose and studythreepreemptionmechanisms • Discard • Buffering • Low priority window • Investigatehow TCP trafficaffectstheproposedsolutions Save thebackgroundtraffic

33. Solutions n n n+1 n+1 … Pb Pa W Pb Pa • Discard • Buffer • Low Priority Window time Routing layer Interface Interface queue

34. Results Discard Mindthe gap Buffer LPW Priority Queuing

35. Conclusions • PTT traffic must be protected • priority queuing is not enough. • Preemptive discard • effective for PTT • devastating for the background traffic. • Buffering and Low Priority Window rescues background traffic • LPW risks reduced priority traffic performance. • Preemption initialization is vulnerable • Racing condition with the TCP background traffic

36. Optimized Group Communication for Tactical Military Networks Erlend Larsen, Lars Landmark, Vinh Pham, Øivind Kure, and Paal. E. Engelstad In proceedings of the IEEE Military Communications Conference (MILCOM), San Jose, CA, USA, October 31–November 4, 2010, pp. 1445–1451, ISBN: 978-1-4244-8179-8.

37. Motivation • PTT and SA traffic have differentQoSrequirements, but must existsimultaneously in the MANET • PTT trafficrequireslow loss and lowlatency • SA traffic is more robust • Bothtraffic types may be forwardedusingmulticast or efficientbroadcast • SMF using S-MPR showedvulnerability to mobility

38. The contributions • Investigating the behavior of S-MPR and NS-MPR • under mobility and varying traffic load. • Employing a radio load metric • to select the better algorithm of S-MPR and NS-MPR. • Dynamicpreemptivechoiceofforwardingalgorithm • to better support thecoexistenceof PTT and SA data in thenetwork

39. MPR  MPR-selector MPR-selector  MPR

40. S-MPR 

41. NS-MPR  

42. SMF forwarding with CF, S-MPR or NS-MPR Classic Flooding – All nodes forward once S-MPR – Source-based MPR forwarding NS-MPR – NON-Source-based MPR forwarding All MPRs forward

43. S-MPR and NS-MPR behavior • S-MPR is vulnerable for mobility and collisions • NS-MPR results in more transmissions per packet

44. Radio loadmetric • A node canobservethelocal radio usage and selectwhichalgorithm to use for forwardingbasedonthe radio load. • For highloads, S-MPR should be preferred • For lowloads, the NS-MPR should be preferred • In case ofmobility, the radio loadwill be reducedwith S-MPR, making sure more nodes employ NS-MPR. • NS-MPR is better at mobility. • The performanceofthe radio loadthresholdsliebetweenthoseof S-MPR and NS-MPR.

45. Radio loadmetric

46. Preemptiveswitch to S-MPR • PTT traffic is vulnerable to collisions, and collisionsoccurbeforethe radio loadforces SA traffic to be forwardedusing S-MPR • A preemptiveswitch to S-MPR for the SA trafficreducestheimpactof SA trafficonthe PTT traffic

47. Conclusions • Analyzed the behavior of S-MPR and NS-MPR: • NS-MPR – robust, but uses more resources. • S-MPR – vulnerable to mobility. • Proposed a radio load metric to switch between S-MPR and NS-MPR distributedly, handling: • Highofferedload • Mobility • Proposed a preemptive forwarding algorithm switch to S-MPR for the SA traffic. • Optimized the performance of the PTT traffic • Allowing the SA service to operate during a PTT session.

48. Concluding Remarks • MANETs are exposed to many challenges impacting the performance of the network. Some of the challenges have been addressed through this thesis work: • Node or gateway position • Mobility induced link breaks • Loss due to competing traffic • Increased understanding has been provided through this work, and solutions that increase the network performance have been proposed.

49. Thank You!