1. Mobile Ad Hoc Networks: Routing, MAC and Transport Issues Material in this slide set are from a tutorial by Prof. Nitin Vaidya 1

2. Mobile-ad hoc network 2

3. Mobile Ad Hoc Networks Networks formed by wireless hosts which may be mobile Without (necessarily) using a pre-existing infrastructure Routes between nodes may potentially contain multiple hops Roles of node and endsystems are merged 3 Communication Network end system node

4. Mobile Ad Hoc Networks May need to traverse multiple links to reach a destination 4

5. Mobile Ad Hoc Networks (MANET) Mobility causes route changes 5

6. Many Applications Personal area networking –Connect cell phone, laptop, wrist watch Military environments –soldiers, ships Civilian environments –taxi cab network Emergency operations –search-and-rescue –policing and fire fighting 6

7. Why is Routing in MANET different ? Host mobility –link failure/repair due to mobility may have different characteristics than those due to other causes Rate of link failure/repair may be high when nodes move fast New performance criteria may be used –route stability despite mobility –energy consumption 7

8. Classification Many protocols have been proposed 8 Ad hoc routing protocols Reactive protocols Proactive protocols Hybrid Traditional distributed shortest-path protocols Maintain routes between every host pair at all times Based on periodic updates; High routing overhead Example: DSDV (destination sequenced distance vector) Determine route if and when needed Source initiates route discovery Example: DSR (dynamic source routing)

9. Trade-Off Latency of route discovery –Proactive protocols may have lower latency since routes are maintained at all times –Reactive protocols may have higher latency because a route from X to Y will be found only when X attempts to send to Y Overhead of route discovery/maintenance –Reactive protocols may have lower overhead since routes are determined only if needed –Proactive protocols can (but not necessarily) result in higher overhead due to continuous route updating Which approach achieves a better trade-off depends on the traffic and mobility patterns 9

10. Flooding of Control Packets Many ad-hoc routing protocols perform (potentially limited) flooding of control packets –The control packets are used to discover routes –Discovered routes are subsequently used to send data packet(s) –Overhead of control packet flooding is amortized over data packets transmitted between consecutive control packet floods 10

11. Dynamic Source Routing (DSR) When node S wants to send a packet to node D, but does not know a route to D, node S initiates a route discovery Source node S floods Route Request (RREQ) Each node appends own identifier when forwarding RREQ 11

12. Route Discovery in DSR 12 B A S E F H J D C G I K Z Y Represents a node that has received RREQ for D from S M N L

13. Route Discovery in DSR 13 B A S E F H J D C G I K Represents transmission of RREQ Z Y Broadcast transmission M N L [S] [X,Y] Represents list of identifiers appended to RREQ

14. Route Discovery in DSR 14 B A S E F H J D C G I K Z Y M N L [S,E] [S,C]

15. Route Discovery in DSR 15 B A S E F H J D C G I K Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once Z Y M N L [S,C,G] [S,E,F]

16. Route Discovery in DSR 16 B A S E F H J D C G I K Z Y M Nodes J and K both broadcast RREQ to node D Since nodes J and K are hidden from each other, their transmissions may collide N L [S,C,G,K] [S,E,F,J]

17. Route Discovery in DSR 17 B A S E F H J D C G I K Z Y Node D does not forward RREQ, because node D is the intended target of the route discovery M N L [S,E,F,J,M]

18. Route Discovery in DSR Destination D on receiving the first RREQ, sends a Route Reply (RREP) RREP is sent on a route obtained by reversing the route appended to received RREQ RREP includes the route from S to D on which RREQ was received by node D 18

19. Route Reply in DSR 19 B A S E F H J D C G I K Z Y M N L RREP [S,E,F,J,D] Represents RREP control message

20. Route Reply in DSR Route Reply can be sent by reversing the route in Route Request (RREQ) only if links are guaranteed to be bi- directional –To ensure this, RREQ should be forwarded only if it received on a link that is known to be bi-directional 20

21. Dynamic Source Routing (DSR) Node S on receiving RREP, caches the route included in the RREP When node S sends a data packet to D, the entire route is included in the packet header –hence the name source routing Intermediate nodes use the source route included in a packet to determine to whom a packet should be forwarded 21

22. Data Delivery in DSR 22 B A S E F H J D C G I K Z Y M N L DATA [S,E,F,J,D] Packet header size grows with route length

23. DSR Optimization: Route Caching Each node caches a new route it learns by any means When node S finds route [S,E,F,J,D] to node D, node S also learns route [S,E,F] to node F When node K receives Route Request [S,C,G] destined for node, node K learns route [K,G,C,S] to node S When node F forwards Route Reply RREP [S,E,F,J,D], node F learns route [F,J,D] to node D When node E forwards Data [S,E,F,J,D] it learns route [E,F,J,D] to node D A node may also learn a route when it overhears Data packets 23

24. Use of Route Caching 24 B A S E F H J D C G I K [P,Q,R] Represents cached route at a node M N L [S,E,F,J,D] [E,F,J,D] [C,S] [G,C,S] [F,J,D],[F,E,S] [J,F,E,S] Z

25. Use of Route Caching: Can Speed up Route Discovery 25 B A S E F H J D C G I K Z M N L [S,E,F,J,D] [E,F,J,D] [C,S] [G,C,S] [F,J,D],[F,E,S] [J,F,E,S] RREQ When node Z sends a route request for node C, node K sends back a route reply [Z,K,G,C] to node Z using a locally cached route [K,G,C,S] RREP

26. Use of Route Caching: Can Reduce Propagation of Route Requests 26 B A S E F H J D C G I K Z Y M N L [S,E,F,J,D] [E,F,J,D] [C,S] [G,C,S] [F,J,D],[F,E,S] [J,F,E,S] RREQ Assume that there is no link between D and Z. Route Reply (RREP) from node K limits flooding of RREQ. [K,G,C,S] RREP

27. Dynamic Source Routing Advantages Routes maintained only between nodes who need to communicate –reduces overhead of route maintenance Route caching reduces route discovery overhead A single route discovery may yield many routes to the destination 27 Disadvantages Packet header size grows with route length due to source routing Flood of route requests Route Reply Storm problem –Reply storm may be eased by preventing a node from sending RREP if it hears another RREP with a shorter route

28. Ad Hoc On-Demand Distance Vector Routing (AODV) DSR includes source routes in packet headers Resulting large headers can sometimes degrade performance –particularly when data contents of a packet are small AODV attempts to improve on DSR by maintaining routing tables at the nodes, so that data packets do not have to contain routes AODV retains the desirable feature of DSR that routes are maintained only between nodes which need to communicate 28

29. AODV Route Requests (RREQ) are forwarded in a manner similar to DSR When a node re-broadcasts a Route Request, it sets up a reverse path pointing towards the source –AODV assumes symmetric (bi-directional) links When the intended destination receives a Route Request, it replies by sending a Route Reply Route Reply travels along the reverse path set-up when Route Request is forwarded 29

30. Route Requests in AODV 30 B A S E F H J D C G I K Z Y Represents a node that has received RREQ for D from S M N L

31. Route Requests in AODV 31 B A S E F H J D C G I K Represents transmission of RREQ Z Y Broadcast transmission M N L

32. Route Requests in AODV 32 B A S E F H J D C G I K Represents links on Reverse Path Z Y M N L

33. Reverse Path Setup in AODV 33 B A S E F H J D C G I K Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once Z Y M N L

34. Reverse Path Setup in AODV 34 B A S E F H J D C G I K Z Y M N L

35. Reverse Path Setup in AODV 35 B A S E F H J D C G I K Z Y Node D does not forward RREQ, because node D is the intended target of the RREQ M N L

36. Route Reply in AODV 36 B A S E F H J D C G I K Z Y Represents links on path taken by RREP M N L

37. Route Reply in AODV An intermediate node (not the destination) may also send a Route Reply (RREP) provided that it knows a more recent path than the one previously known to sender S To determine whether the path known to an intermediate node is more recent, destination sequence numbers are used The likelihood that an intermediate node will send a Route Reply when using AODV not as high as DSR –A new Route Request by node S for a destination is assigned a higher destination sequence number. An intermediate node which knows a route, but with a smaller sequence number, cannot send Route Reply 37

38. Forward Path Setup in AODV 38 B A S E F H J D C G I K Z Y M N L Forward links are setup when RREP travels along the reverse path Represents a link on the forward path

39. Data Delivery in AODV 39 B A S E F H J D C G I K Z Y M N L Routing table entries used to forward data packet. Route is not included in packet header. DATA

40. Summary: AODV Routes need not be included in packet headers Nodes maintain routing tables containing entries only for routes that are in active use At most one next-hop per destination maintained at each node –DSR may maintain several routes for a single destination Unused routes expire even if topology does not change 40

41. Link State Routing Each node periodically floods status of its links Each node re-broadcasts link state information received from its neighbor Each node keeps track of link state information received from other nodes Each node uses above information to determine next hop to each destination 41

42. Optimized Link State Routing (OLSR) The overhead of flooding link state information is reduced by requiring fewer nodes to forward the information A broadcast from node X is only forwarded by its multipoint relays Multipoint relays of node X are its neighbors such that each two-hop neighbor of X is a one-hop neighbor of at least one multipoint relay of X –Each node transmits its neighbor list in periodic beacons, so that all nodes can know their 2-hop neighbors, in order to choose the multipoint relays 42

43. Optimized Link State Routing (OLSR) Nodes C and E are multipoint relays of node A 43 A B F C D E H G K J Node that has broadcast state information from A

44. Optimized Link State Routing (OLSR) Nodes C and E forward information received from A 44 A B F C D E H G K J Node that has broadcast state information from A

45. Optimized Link State Routing (OLSR) Nodes H and A are multipoint relays for node E Node H forwards information received from E 45 A B F C D E H G K J Node that has broadcast state information from A

46. Advantages Routing table always available Suitable for dense networks where frequent communication is required between a (relative) large number of nodes. Disadvantages Flooding (even if limited) Unsuitable for sensor networks Routes used by OLSR only include multipoint relays as intermediate nodes OLSR

47. Destination-Sequenced Distance-Vector (DSDV) Each node maintains a routing table which stores –next hop towards each destination –a cost metric for the path to each destination –a destination sequence number that is created by the destination itself –Sequence numbers used to avoid formation of loops Each node periodically forwards the routing table to its neighbors –Each node increments and appends its sequence number when sending its local routing table –This sequence number will be attached to route entries created for this node 47

48. Destination-Sequenced Distance-Vector (DSDV) Assume that node X receives routing information from Y about a route to node Z Let S(X) and S(Y) denote the destination sequence number for node Z as stored at node X, and as sent by node Y with its routing table to node X, respectively 48 XY Z

49. Destination-Sequenced Distance-Vector (DSDV) Node X takes the following steps: –If S(X) > S(Y), then X ignores the routing information received from Y –If S(X) = S(Y), and cost of going through Y is smaller than the route known to X, then X sets Y as the next hop to Z –If S(X) < S(Y), then X sets Y as the next hop to Z, and S(X) is updated to equal S(Y) 49 XY Z

50. Spanning Tree Protocol A routing algorithm for mobile self-organizing networks

51. 51 Spanning Tree Protocol Adaptation of Perlman’s algorithm for bridges Assumption –Substrate has broadcast operation (e.g., 802.11b) Components –Builds a rooted tree topology –All node agree on a common root –Each node selects a parent –Each node broadcasts beacon messages periodically –Unicast and multicast forwarding

52. Spanning Tree Protocol Assumption –Wireless channel can be asymmetric –Outgoing broadcast packet can be received by adjacent nodes –Each node has a unique Identifier (an integer number) Components –A shared tree topology –Periodic beacon messages –Configurable topology policy (parent selection algorithm)

53. Tree-based topology Advantages –Topology is always maintained –Easy to do broadcasting (loop-free) –A shared tree is guaranteed given that there’s no partition Disadvantages – No redundancy – Message may not travel on most efficient path –Difficult to do unicast

54. Spanning Tree Protocol: Beacon Message Periodically each node sends a beacon to its adjacent nodes –Used as in IEEE 802.1b: Used to select parents in spanning tree –Probes link quality

55. Spanning Tree Protocol IDLink Quality LQ/RLQ Time Stamp 4769/101098900558838 1672/101098900559750 2508/101098900558724 Adjacency Table –Record the link state of adjacent nodes –Being updated by beacon message received from others Link Quality –Measured by counting the number of beacons from the sender during a specified period Functions –Eliminate asymmetric links –Eliminate bad quality links –Used in topology algorithm LQ = %beacon received from this node RLQ= %beacon delivered to this node BiLQ= Min(LQ, RLQ)

56. Root and parent selection Root selection –The node with minimum ID is the root Parent selection –Choose the node that broadcasts the smaller root ID –When two nodes broadcast the same root ID Minimum Hop Algorithm: choose the node that has the minimum hop count to root Path Quality Algorithm: choose the node that has the best path to root Path Quality = Product of the BiLQs of all links on the path

57. Minimum Hop vs. Path Quality Minimum Hop –Widely used in current ad-hoc routing protocols –Has good performance in simulator, e.g., GlomoSim –Tends to select distant links that has worse link quality in real 802.11 network Path Quality –Tends to have longer path –Favors the path with lower loss rate –Doesn’t show better performance in simulator –Does show large improvement in real 802.11 network

58. Routing in SPT Multicast –Sends along the tree edges Unicast –Maintains routing table –Routing table can be updated passively or actively data Dest IDNextHop ID Time Stamp 4762711098900558838 1671231098900559750 25041098900558724

59. rreq Updating Routing Table Passive updating (Learning) Active updating (Route Request) data data:5 rreq rrep Create a pathInvalidate a path data:5 rreq

60. Simulation Result Platform: GlomoSim 10 unicast data streams Compared to AODV

61. Mobility Experiment 6 PDAs are fixed at location, and 1 moves around Using UDP adapter Sender sends out 10 packets per second by unicast to the moving node, and no ACKs. Randomized logical address

62. Mobility Experiment Minimum Hop Path Quality