1. Kyle Fitzpatrick Konstantin Zak
Wireless Routing
Kyle Fitzpatrick
Konstantin Zak

2. Outline Background Routing problem Protocols Comparisons Conclusion
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
Wireless

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

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

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
Freedom from loops

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 Acknowledgments
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 Route table Route request expiration timer
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) RREQ is broadcasted
< 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
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
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
A. Salam. “Mesh Networks.” School of Digital Radio Communications for Research and Training in Developing Countries. Latin American Networking School. February 2004.