1. Sensor Network Routing
Week 10 Lecture 1

2. Start from: A Review of Current Routing Protocols for Ad Hoc Mobile Wireless Networks

3. Mobile Ad Hoc Wireless Networks
Unreliable wireless medium
Mobile nodes
No central authority
Traffic patterns - application specific
Energy constraints

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

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
Reactive
Proactive
Hybrid
Source-initiated
on-demand
Table driven
Hybrid
DSDV
OLSR
WRP
ZRP
CGSR
AODV
DSR
TORA
ABR
SSR

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 Routing Table of Node A
Destination
Next
Metric
Seq. Nr A
A-550 B 1
B-102 C 2
C-588 D 3
D-312
Routing Table of Node A A B C D
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 S E F B C D A G H I
Represents a node that has received RREQ for D from S

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

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

18. Reverse Path Setup in AODVF B C D A G H 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 S E F B C D A G H 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 S E F B C D A G H I
Represents a node that has received RREQ for D from S

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

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

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

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 (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(n2) time and message complexity to stabilize

29. TORA Example A B F C E G D
DAG maintained to destination D

30. TORA Example A B F C E G Link (G,D) broke D
Node G has no outgoing links

31. TORA Example A B F C E G Represents a link that was reversed recently
Now nodes E and F have no outgoing links

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

33. TORA Example A B F C E G Represents a link that was reversed recently
Now node A has no outgoing links

34. TORA Example A B F C E G Represents a link that was reversed recently
Now all nodes (except destination D) have outgoing links

35. TORA Example A B F C E G 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