Mobile Ad hoc NETwork (MANET)

1. Mobile Ad hoc NETwork (MANET)

2. Outline • MANET overview • Applications of MANET • Issues in MANET • MAC Protocols for MANET • Routing Protocols for MANET • Open issues and future directions

3. Infrastructure networks (single hop) • Cellular networks • IEEE 802.11

4. Mobile Ad Hoc Networks • Formed by wireless autonomous hosts • Without (necessarily) using a pre-existing infrastructure • Routes between hosts may potentially contain multiple hops • Host mobility cause route changes • Shared wireless channel

5. MH2 MH4 Asymmetric link MH3 MH5 MH7 Symmetric link MH1 MH6 Mobile Ad Hoc Networks

6. Why Ad Hoc Networks ? • Ease of deployment • Speed of deployment • Decreased dependence on infrastructure • User flexibility

7. Application areas • Military environments • Battle field: sensors, soldiers, vehicles • Emergency operations • search-and-rescue • policing and fire fighting • Civilian environments • conference halls • sports stadiums, Library, etc. • Personal area networking • laptop, PDA, cell phone, ear phone, wrist watch

8. Challenges & Issues • Medium Access Control • Distributed Operation • Synchronization • Hidden & Exposed terminal problem • Access delay and Fairness • Real Time Traffic support • Low bandwidth • Ease of snooping on wireless transmissions • Routing • Mobility-induced route changes/packet losses • High BER • Location-dependent contention • Looping • Distributed Routing

9. Challenges & Issues • Transport Layer Protocols • UDP – Highly Unreliable, may result into increasing congestion • TCP – Frequent path breaks, stale routing information, high error rate, frequent network partitions. • Energy Management • Battery energy management • Transmission Power management • Processor and device power management • Security • Denial of Service attack (DoS) • Resource Consumption • Energy Depletion • Buffer Overflow • Compromised Nodes • Interference

10. Challenges & Issues • Deployment Constraints • Environment • Area of Coverage • Asymmetric Capabilities • transmission ranges • battery life • processing capacity • Speed/pattern of movement

11. MAC Protocols • Goals • Operation should be distributed • Support QoS for Real Time data • Minimize Access Delay • Fairness • Scalable • Power Control Mechnism • Adaptive Rate Control • Synchronization

12. MAC Protocols Classification of MAC Protocols • Contention-Based • Contention-Based with Reservation • Contention-Based with Scheduling

13. Why is Routing in MANET Different? • Host mobility • link failure/repair due to mobility • different characteristics than those due to other causes • Rate of link failure/repair may be high when nodes move fast • Distributed Environment • New performance criteria may be used • Route stability despite mobility • Packet delivery ratio • Routing Overhead

14. Routing Protocols in MANET • Goals • Fully Distributed • Adaptive to frequent topology changes • Route computation and maintenance must involve minimum number of nodes • Routing state must be localized • Must be loop free and free from stale route • Converge must be quick • Efficient resource utilization like BW, comp power, battery, memory • Provide QoS

15. Ad hoc Routing Protocols • Proactive protocols (Table Driven) (Eg.DSDV) • Reactive protocols (On-Demand)(Eg. AODV, DSR) • Hybrid protocols (ZRP, CEDAR) • Which approach achieves a better trade-offdepends on the traffic and mobility patterns

16. Proactive Protocols • Each node maintains a table having consistent, up-to-date routing information from each node to every other node. • Respond to changes by propagating updates to throughout the network • Variations are on basis of number of tables required and the way updates are propagated. • Features: • Traditional distributed shortest path routing protocols • link-state or distance-vector protocol • Examples • Destination-Sequenced Distance-Vector (DSDV) • Clusterhead Gateway Switch Routing (CGSR) • The Wireless Routing Protocol (WRP)

17. Reactive Protocols • Creates route only when desired by the source node • Source initiates a route discovery process within the network • Once a route has been established, it is maintained by some form of route maintenance procedure • Features: • Maintain routes only if needed • Flooding of control message • higher latency and lower overhead • Source routing/hop-by-hop routing • Examples • Ad hoc On Demand Distance Vector Protocol (AODV) • Dynamic Source Routing Protocol (DSR) • Temporally-Ordered Routing Algorithm (TORA) • Associativity-Based Routing (ABR) • Signal Stability Routing (SSR)

18. Hybrid Protocols • Hybrid routing protocols are proposed to combine the merits of both proactive and reactive routing protocols and overcome their shortcomings. • Features: • Constrained link state maintenance • Route established on-demand • Examples • Zone Routing Protocol (ZRP) • Core-Extraction Distributed Adhoc Routing (CEDAR)

19. DSDV • Destination Sequenced Distance Vector routing protocol • Proactive • Each node maintains its own sequences number • Updates (increments) at each change in neighborhood information • Used for loop freedom • Each node maintains routing table with entry for each node in the network

20. DSDV --- Routing Table at MN4 Dest Nexthop Metric DestSequence MN1 MN2 2 406 MN2 MN2 1 128 MN3 MN2 2 564 MN4 MN4 0 710 MN5 MN6 2 392 MN6 MN6 1 076 MN7 MN6 2 128 MN8 MN6 3 050

21. DSDV routing updates • Each node periodically transmits updates • Includes its own sequences number, routing table updates • Nodes also send routing table updates for important link changes • When two routes to a destination received from two different neighbors • Choose the one with greatest destination sequence number • If equal, choose the smaller metric (hop count)

22. DSDV --- full dump • Full Dumps • Carry all routing table information • Transmitted relatively infrequently • Incremental updates • Carry only information changed since last full dump • Fits within one network protocol data unit • If can’t, send full dump

23. DSDV --- link additions • When A joins network • Node A transmits routing table: <A, 101, 0> • Node B receives transmission, inserts <A, 101, A, 1> • Node B propagates new route to neighbors <A, 101, 1> • Neighbors update their routing tables: <A, 101, B, 2> and continue propagation of information

24. DSDV --- link breaks • Link between B and D breaks • Node B notices break • Update hop count for D and E to be infinity • Increments sequence number for D and E • Node B sends updates with new route information • <D, 203, infinite> • <E, 156, infinite>

25. DSDV --- Summary • Routes maintained through periodic and event triggered routing table exchanges • Incremental dumps and settling time used to reduce control overhead • Lower route request latency, but higher overhead • Perform best in network with low to moderate mobility, few nodes and many data sessions • Problems: • Not efficient for large ad-hoc networks • Nodes need to maintain a complete list of routes.

26. Clusterhead Gateway Switch Routing (CGSR) • Similar to DSDV except addressing being employed and network organization • Node are grouped into clusters. Clusterhead selection algo (Least Cluster Change) is employed to elect a clusterhead • Gateways are used to relay packets between clusterheads. • Each node maintains cluster member table which stores destination cluster head for each node. • Also they maintain routing table, like DSDV to find next hop

27. CGSR---Routing Routing from Node 1 to Node 8

28. CGSR--- Summary • Easy to implement scheduling • Better utilization of resources • Problems: • Increase in path length • Instability at high mobility

29. The Wireless Routing Protocol (WRP) • Each node maintains 4 tables: • Distance table • Routing table • Link-cost table • Message retransmission list (MRL) • DT contains matrix where each element contains distance and penultimate node reported by neighbor of a particular destination • MRL contains sequence no of update message, retransmission counter, ack required flag for each neighbor, list of update sent in update message

30. AODV • The Ad-hoc On-Demand Distance Vector Algorithm • Reactive • Pure on-demand route acquisition system • Route discovery cycle used for route finding • Maintenance of active routing • Sequence number used for loop prevention and route freshness criteria • Descendant of DSDV • Provides unicast and multicast communication

31. AODV --- Goal • Quick adaptation under dynamic link conditions • Lower transmission latency • Consume less network bandwidth (less broadcast) • Loop-free property • Scalable to large network

32. AODV --- unicast route discovery • RREQ (route request) is broadcast • Sequence Number: • Source SN: freshness on reverse route to source • Destination SN: freshness on route to destination • RREQ message • <bcast_id, dest_ip, dest_seqno, src_seqno, hop_count> • While forwarding, intermediate nodes record address of neighbor from where first copy of RREQ is received, thus creating reverse path.

33. AODV --- unicast route discovery • RREP (route reply) is unicast back • From destination if necessary • From intermediate node if that node has a recent route • Intermediate node forwarding RREP stores this info in their routing cache to set up a path to destination • Route timer is maintained with each entry. If idle for some time delete that route • As RREP is always forwarded over path of RREQ, it always expects symmetric links.

34. AODV --- route discovery (1) • Node S needs a route to D • Create a route request (RREQ) • Enters D’s IP address, sequence number, S’s IP address, sequence number • Broadcasts RREQ to neighbors

35. AODV --- route discovery (2) • Node A receives RREQ • Makes reverse route entry for S • Dest = S, nexthop = S, hopcount = 1 • It has no route to D, so it broadcasts RREQ • Node C receives RREQ • Makes reverse route entry for S • Dest = S, nexthop = A, hopcount = 2 • It has route to D && seq# for route D > seq# in RREQ • Creates a route reply (RREP) • Enters D’s IP address, sequence number, S’s IP address, hopcount • Unicasts RREP to A

36. AODV --- route discovery (3) • Node A receives RREP • Unicasts RREP to S • Makes forward route entry to D • Dest = D, nexthop = C hopcount = 2 • Node S receives RREP • Makes forward route entry to D • Dest = D, nexthop = A hopcount = 3 • Sends data packets on route to D

37. AODV --- route maintenance (1) • Link between C and D breaks • Node C invalidates route to D in routing table • Node C creates route error (RERR) message • Lists all destinations which are now unreachable • Sends to upstream neighbors • Node A receives RERR • Checks whether C is its next hop on route to D • Deletes route to D, and forwards RERR to S

38. AODV --- route maintenance (2) • Node S receives RERR • Checks whether A is its next hop on route to D • Deletes route to D • Rediscovers route if still needed

39. AODV --- Optimizations • Expanding ring search • Prevents flooding of network during route discovery • Control Time to Live of RREQ • Local repair • Repair breaks in active routes locally instead of notifying source • If first repair attempt is unsuccessful, send RERR to source

40. AODV --- Summary • Reactive / On-demand • Sequence numbers used for route freshness and loop prevention • Route discovery cycle • Maintains only active routes • Optimization can be used to reduce overhead and increase scalability

41. Dynamic Source Routing (DSR) • Two Phases • Route discovery • Route maintenance • Before transmitting, a node consults its route cache. If unexpired route available, use that route else begin route discovery by broadcasting route request pkt. • RREQ contains add of Dest, Source Add, unique ID

42. Dynamic Source Routing (DSR) • Node receiving the pkt checks, if it knows the route to destination. If it does not then adds its own address to record route and forward the pkt to next neighbor. • RREP is generated by destination or any intermediate node knowing path to destination. • Responding node can use path to initiator for RREP if available else if symmetric links are supported, reverse path in record route. • If symmetric links are not supported, initiate RREQ with RREP being piggybacked

43. DSR

44. Dynamic Source Routing (DSR) • Route Maintenance – Whenever a link breakage is noticed, route error pkt is generated and broadcated and route containing that hop is deleted. • Apart from error pkt, ack is used to check correct operation of links (typically passive ack)

45. Associativity Based Routing (ABR) • Route selection based stability of a route • Stability is measured based count of beacons • If a beacon is not received for some interval, count is set to zero for a link • A link is stable is it is leading to a stable neighbor and same way unstable link

46. Associativity Based Routing (ABR) • RREQ is flooded • Intermediate nodes forwards RREQ by appending its address and beacon count in it. • When it reaches destination, dest waits for TRouteSelectTime to receive more RREQ from different paths • Select route with maximum proportion of stable links • If two routes with same proportion of stable links, then choose shorter one. • But more priority is given to stability than length

47. Associativity Based Routing (ABR) • Route Maintenance • If a link is down, neighbor node detects the breakage of link and initiates local recovery by broadcasting route repair pkt called Local Query(LQ) broadcast with limited TTL (Ex 2) • Advantages & Disadvantages • Routes are stable so less chance of link failure • Cons: Path may be longer • Repetition of LQ

48. Hybrid Protocols • Proactive protocol: • Pro-actively updates network state and maintains route regardless of whether any data traffic exists or not • Reactive protocol: • Only determines route to a destination if there is some data to be sent to the destination

49. Zone Routing Protocol(ZRP) • Uses best features of reactive and proactive • Uses proactive routing within a zone and reactive outside the zone • Intra Zone Routing Protocol (IARP) and Inter Zone Routing Protocol (IERP) • A routing zone of a given node is subset of nw within which all nodes are reachable within less than or equal to zone radius hops • Interior nodes and peripheral nodes • Each nodes maintains info abt all nodes in the zone by periodic route update pkt (IARP)

50. Zone Routing Protocol(ZRP) • When a pkt from s is to be transmitted to d • S checks whether d is in its routing zone, if yes it uses proactive routing table • If no it broadcasts RREQ to all peripheral nodes • If they know they respond with RREP else they also forward to their peripherals until the destination is reached • All forwarding (RREQ) nodes appends their address to the RREQ to deliver RREP on that path • Broken link is handled by local repair and a path update message is sent to source