Wireless Routing

1. Wireless Routing Kyle Fitzpatrick Konstantin Zak

2. Outline • Background • Routing problem • Protocols • Table driven • On-demand driven • Comparisons • Conclusion • References

3. Background • 1970s – Wireless networks first appeared • 1980s – First mobile networks • Present – Two variations of mobile wireless networks • Infrastructured • Infrastructureless

4. Infrastructured • Fixed access points • Mobile units only communicate with AP • Handoff between APs as mobile unit moves • Typical applications include office wireless networks

5. Infrastructureless • Ad-hoc network • No fixed routers • Every node responsible for routing

6. Ad-hoc Networks • Dynamic topology • Self organizing • High bandwidth • Spatial reuse

7. Wireless Routing Problem • Discover routes between nodes • Avoid loops • Avoid high power consumption • Low bandwidth • High error rates • Limited memory

8. Maintain routing information for all nodes Broadcasts network changes Creates routes only when needed Recent routes cached Table driven vs. On-demand

9. Existing Protocols

10. Table Driven Protocols

11. Destination-Sequenced Distance-Vector Routing (DSDV) • Based on Bellman-Ford routing mechanism • Nodes maintain table for of all possible destinations with number of hops to each

12. Bellman-Ford • Columns of table represent the directly attached neighbors • Rows represent all destinations in the network • Contains the path for sending packets to each destination in the network and distance/or time to transmit on that path (we call this "cost"). • The measurements in this algorithm are the number of hops, latency, the number of outgoing packets, etc.

13. Problems with BF • Counting to infinity • Routing loops

14. DSDV Solution • Tag each route table entry with a sequence number • Distinguish stale routes from new ones, thus avoid loops

15. New Route Broadcasts • Destination address • Number of hops • Sequence number from destination, as originally stamped by destination • Unique sequence number for broadcast

16. Route update • Routing table updates transmitted throughout network for consistency • To avoid network congestion, two kinds of packets are sent • “full dump,” carries all available routing information • Smaller packets used to relay routing changes since last dump

17. Proof of Loop-free Property

18. Clusterhead Gateway Switch Routing (CGSR) • Uses DSDV as underlying routing scheme • Instead of “flat” network, CGSR is a clustered multi-hop • Cluster head selection algorithm • Gateway nodes within communication of two cluster heads

19. Routing from Node 1 to Node 8

20. Wireless Routing Protocol (WRP) • Each node maintains four tables • Distance table • Routing table • Link-cost table • Message retransmission • Update messages inform each other of link changes • “hello” messages sent periodically

21. Loop Freedom • Communicate the distance and second-to-last hop info for each destination • Avoids “count-to-infinity” • nodes perform consistency checks of predecessor information from neighbors

22. On-Demand Protocols

23. Dynamic Source Routing (DSR) • Mobile nodes maintain route caches with complete routes to destinations. • Multiple routes per destination allowed • Route caches updated continually • Two phase protocol: • Route discovery • Route maintenance

24. Route Discovery • Route request packet • Destination address • Source node address • Unique identification number • Route record

25. Route Request

26. Route Discovery, cont. • Route reply returns route record to initiator • Obtain return route from: • Route cache • Reverse route record • Route discovery packet

27. Route Reply

28. Route Maintenance • Route error packets • Cache entries for lost node removed • Other routes truncated at lost node • Acknowledgments • Active • Passive

29. Signal Stability Routing (SSR) • Two cooperative protocols • Dynamic Routing Protocol (DRP) • Static Routing Protocol (SRP) • Routes chosen based on signal strength and location stabilty.

30. Dynamic Routing Protocol • Signal Stability Table (SST) • Periodic beacons • Signal strength (strong or weak) • Routing Table (RT) • Stores path to destinations • Only route requests from strong channels are processed

31. Static Routing Protocol • Passes packets up stack • Forwards packets • Initiates route search

32. Temporally-Ordered Routing Algorithm (TORA) • Designed for highly dynamic topologies • Provides multiple routes • Utilizes a time based height metric • Requires synchronized clocks

33. Ad-hoc On-Demand Distance Vector Routing (AODV) • Routes as needed • Periodic advertisements optional • Scales to large topologies • Requires neighbors detect each others’ broadcasts

34. AODV Goals • Broadcast discovery packets only when necessary • Distinguish between local connectivity and general topology • Only disseminate topology changes to neighbors likely to need it

35. An AODV Node • Two counters • Node sequence number • Broadcast_id • Route table • Route request expiration timer

36. Route Table • Destination • Next hop • Number of hops • Destination sequence number • Active neighbors • Route expiration time

37. Path Discovery • Initiated with route request (RREQ) < source_addr, source_seq_#, broadcast_id, dest_addr, dest_seq_#, hop_cnt > • RREQ is broadcasted • Nodes either satisfy RREQ or rebroadcast it • RREQs are satisfied with a route reply (RREP)

38. Reverse Path • Intermediate nodes store: • Destination IP • Source IP • Broadcast_id • Reverse path expiration time • Source sequence number

39. Forward Path • Conditionals for route reply • Has route? • Bi-directional link? • >= dest_seq_#? • If the above conditions are met then a route reply (RREP) is issued < source_addr, dest_addr, dest_seq_#, hop_cnt, lifetime>

40. Path Maintenance • Link failure detection • Periodic “hello” messages • Link-layer acknowledgements • Nodes issue special RREP with hop_cnt equal to ∞. • RREP propagates to all active neighbors

41. Future Development • Multicast • Elimination of “hello” messages • Intermediate node route rebuilding

42. AODV Summary • Nodes store only needed routes • Broadcasts minimized • Quick link failure response • Loop-free routes • Scalable to large topologies

43. Comparisons

44. Table-Driven Comparison • DSDV inefficient due to requirement of periodic updates, regardless of topology changes • CSGR performance improved due to token scheduling, gateway code scheduling, and path reservation • “hello” packets WRP don’t allow nodes to sleep

45. Table-Driven Routing Protocols

46. Source-Initiated On-Demand Routing Comparison • DSR has more overhead then AODV since packets carry full routing information • SSR paths tend to be longer lived, hence higher throughput • TORA supports multiple routes • Unlike AODV and DSR, intermediate routes can’t reply to route requests sent toward destination, causing delays

47. Source-Initiated On-Demand Routing Protocols

48. Conclusion • Reasons for choosing AODV • Small memory requirements • Limits power consumption • Flexible • Scalable

49. References • E.M. Royer, C-K Toh. “A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks,” IEEE Personal Com., April 1999, pp. 46-55. • C.E. Perkins, E.M. Royer. “Ad Hoc On Demand Distance Vector Routing,” Proceedings of 2nd IEEE Workshop on Mobile Computing Systems and Applications, February 1999. • C.E. Perkins, P. Bhagwat. “Highly Dynamic Destination-Sequenced Distance-Vector Routing (DSDV) for Mobile Computers.” Computer Communications Review, October 1994, pp. 234-244. • D.B. Johnson, D.A. Maltz, J. Broch. “DSR: The Dynamic Source Routing Protocol for Multi-Hop Wireless Ad Hoc Networks.” Ad Hoc Networking. C.E. Perkins ed., Chapter 5, pp. 139-172. • A. Salam. “Mesh Networks.” School of Digital Radio Communications for Research and Training in Developing Countries. Latin American Networking School. February 2004.