1. Sensor Network Routing Romit Roy Choudhury and Pradeep Kyasanur (Some slides are based on Dr. Nitin Vaidya’s tutorial)

2. A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks Elizabeth M Royer, Chai-Keong Toh

3. Mobile Ad Hoc Wireless Networks Unreliable wireless medium Mobile nodes No central authority Traffic patterns application specific Energy constraints More information in MANET Charter

4. Example Ad Hoc Network B A E F H C G I D Nodes have unique identifiers Routing problem – find path between S and D S

5. Classification of routing protocols Table-driven (proactive) –Up-to-date routing information maintained –Routing overhead independent of route usage Source-initiated (demand-driven / reactive) –Routes maintained only for routes in use –Explicit route discovery mechanism Hybrid Protocols –Combination of proactive and reactive

6. Classification (cont.) Ad Hoc Routing Protocols Table driven Source-initiated on-demand DSDV WRP AODV DSR TORAABR SSR Reactive Proactive Hybrid ZRP Hybrid OLSR CGSR

7. Table-driven Routing Protocols Each node maintains a routing table –Contains routes to all nodes in the network Changes to network topology is immediately propagated Protocols differ in mechanisms used to propagate topology information

8. Destination Sequenced Distance Vector (DSDV) Based on Bellman-Ford algorithm Enhanced with sequence number to avoid loops –Fresher routes have higher sequence numbers Optimizations added to reduce routing overheads – incremental data exchange, delayed exchange of updates

9. DSDV Example DestinationNextMetricSeq. Nr AA0A-550 BB1B-102 CB2C-588 DB3D-312 A B C D Routing Table of Node A Route information is exchanged periodically

10. Clusterhead Gateway Switch Routing (CGSR) Nodes organized into hierarchy of clusters. Each node has a clusterhead, selected using an election. Nodes send packet through clusterheads. Clusterheads communicate amongst themselves using DSDV. –Two clusters are connected through a gateway node

11. Wireless Routing Protocol (WRP) Maintains multiple tables –Distance, routing, link-cost, etc. Link change messages exchanged only between neighbors Loop freedom using novel algorithm –Uses predecessor hop information

12. Other Table-Driven Protocols Optimized Link State Routing Protocol (OLSR) – RFC 3626 –Optimization of link-state routing to wireless Topology Dissemination Based on Reverse Path Forwarding (TBRPF) - RFC 3684 –Also based on link-state routing

13. Source-Initiated On-Demand Routing Create routes only when needed Routes found using a “route discovery” process Route maintenance procedure used to repair routes

14. Ad Hoc On-Demand Distance Vector Routing (AODV) Now RFC 3561, based on DSDV Destination sequence numbers provide loop freedom Source sends Route Request Packet (RREQ) when a route has to be found Route Reply Packet (RREP) is sent back by destination Route Error messages update routes

15. Route Requests in AODV B A S E F H C G I Represents a node that has received RREQ for D from S D

16. Route Requests in AODV B A S E F H C G I Represents transmission of RREQ Broadcast transmission D

17. Route Requests in AODV B A S E F H C G I Represents links on Reverse Path D

18. Reverse Path Setup in AODV B A S E F H D C G I Node C receives RREQ from G and H, but does not forward it again, because node C has already forwarded RREQ once

19. Route Reply in AODV B A S E F H D C G I Represents links on path taken by RREP

20. Dynamic Source Routing (DSR) Similar to AODV in route discovery Full source-route is aggregated in RREQ, and sent back in RREP Each data packet has full source route Route table overhead only at source node However, overhead with each data packet

21. Route Requests in DSR B A S E F H C G I Represents a node that has received RREQ for D from S D

22. Route Requests in DSR B A S E F H C G I Represents transmission of RREQ Broadcast transmission D

23. Route Requests in DSR B A S E F H C G I RREQ keeps a list of nodes on the path from the source D

24. Route Reply in DSR S E F D Represents links on path taken by RREP B A H C G I

25. Associativity-Based Routing Defines metric “Degree of Association Stability” –This metric used instead of shortest hop Nodes with less mobility/better links have higher stability value DSR-like protocol is used for routing

26. Signal Stability Routing Signal strength of links is used as metric DSR-like routing is used RREQ is forwarded only if packet is received over a link with good signal strength

27. Other metrics Expected Transmission Time (ETT) metric –Easier to compute, and more useful than signal strength Weighted Cumulative Expected Transmission Time –Better for multi-radio, and asymmetric rate links

28. Temporally Ordered Routing Algorithm Directed Acyclic Graph (DAG) rooted at destination is used to route packets Link Reversal algorithm used to update DAG (along with notion of “height”) Algorithm is distributed and loop-free Recent result - Link reversal takes O(n 2 ) time and message complexity to stabilize

29. TORA Example AFB CE D DAG maintained to destination D G

30. TORA Example Link (G,D) broke AFB CEG D Node G has no outgoing links

31. TORA Example AFB CE G D Now nodes E and F have no outgoing links Represents a link that was reversed recently

32. TORA Example A F B C EG D Nodes E and F do not reverse links from node G Now node B has no outgoing links Represents a link that was reversed recently

33. TORA Example A FB C EG D Now node A has no outgoing links Represents a link that was reversed recently

34. TORA Example AFB C EG D Now all nodes (except destination D) have outgoing links Represents a link that was reversed recently

35. TORA Example AFB C EG D DAG has been restored with only the destination as a sink

36. Other routing protocols Geographic Routing Protocols –Location Aided Routing (LAR) –Distance Routing Effect Algorithm for Mobility (DREAM) –Greedy Perimeter Stateless Routing (GPSR) Hybrid Routing Protocols –Zone Routing Protocol (ZRP)

37. Discussion Proactive routing protocols suitable for high traffic load, low mobility On-demand routing protocols suitable for low traffic load and/or moderate mobility With high mobility, flooding of data packets may be the only option

38. Locating and Bypassing Routing Holes in Sensor Networks Qing Fang, Jie Gao and Leonidas J. Guibas

39. GPSR Location of the destination node is assumed to be known Each node knows location of its neighbors Each node forwards a packet to its neighbor closest to the destination If routing holes are found, uses perimeter routing (right-hand rule)

40. Routing Holes G D C F B S A E J H HOLE I

41. Problem with GPSR Approach Maintaining perimeter graph expensive, especially in sensor networks Identifying holes (and boundary around holes) useful for routing around them –Also useful for path migration, information storage Node where packets get stuck (due to a hole) define the boundary around holes

42. Definitions Weak stuck node P – P is the closest node to node Q (among P’s neighbors), and Q is out of range of P –Q is called black node P J H Q

43. Definitions Strong stuck node P – P is closest node to point Q, and Q is out of range of P –Collection of Qs is called black region P J H Black Region Q

44. Proposed Algorithms TENT rule – enables detection of strongly stuck nodes P J H O

45. Proposed Algorithms BOUNDHOLE- identifies the boundary of a hole Start with a stuck node, and sweep counter-clockwise Move from stuck node to stuck node till the originating node is reached, completing loop

46. Discussion Identifying “holes” useful for many applications Hole identification assumes “circular” radio transmission pattern –Can a similar algorithm be designed using connectivity properties alone?