1. A comparison of Ad-Hoc Routing Protocols
Alvin AuYoung
CSE 291-B
April 24, 2003

2. A Review of Routing Route discovery
how do I get from source to destination?
Route update
how do I find out if a route has changed?
Stored route state
what route bookkeeping is involved?
Route decision/metric
how do I choose which path to follow?

3. Common Routing Protocols
Distance-Vector
each router maintains a table of its “optimal” path to every other node on the network
tables are broadcast to neighbors and optimal routes from each source to destination are calculated
Link-State
each router maintains data about its closest neighbors and broadcasts this information to all other nodes in network
updates are continuously sent throughout the network; routers use this “global view” to calculate optimal routes

4. Issues in Wireless Networks
Channel Access/Availability
Hidden terminal problem

5. Issues in Ad-hoc Networks
Host mobility
Lack of infrastructure
Unpredictable network topology
Power limitations

6. Issues with existing “wired” routing protocols
Rely on a somewhat stable infrastructure
Do not handle changing network topology very well
Maintain a lot of state

7. On-demand Routing Protocols
Routes are created by some route discovery mechanism “on demand”
Up-to-date Route information is not actively propagated

8. Ad-Hoc Routing Protocols
AODV
Ad-hoc On-demand Distance Vector Protocol
DSR
Dynamic Source Routing

9. AODV Based on standard Distance Vector Algorithm
Nodes maintain route cache and uses destination sequence number for each route entry
Does nothing when connection between end points is still valid
Route Discovery Mechanism is initiated when a route to new destination is needed by broadcasting a Route Request Packet (RREQ).
Route Error Packets (RERR) are used to erase broken links

10. source destination The source broadcasts a route packet
The neighbors in turn broadcast the packet till it reaches the destination
source
RREQ
destination
RREP
Reply packet follows the reverse path of route request packet recorded in broadcast packet
The node discards the packets having been seen

11. DSR Two main mechanisms: Route Maintenance and Route Discovery
Route Discovery mechanism is similar to the one in AODV but with source routing instead
Route Maintenance is accomplished through route caches
Entries in route caches are updated as nodes learn new routes, multiple routes can be stored.

12. source broadcasts a packet containing address of source and destination
(1,4) 1 4
The destination sends a reply packet to source. 8
destination
(1,3) 3 7
(1,4,7) 2
The node discards the packets having been seen
(1,2) 6 5
(1,3,5,6)
(1,3,5)
The route looks up its route caches to look for a route to destination
If not find, appends its address into the packet

13. Comparison: Goals Packet Delivery Fraction
End-to-end Delay of Data Packets
Normalized Routing load
Normalized MAC load

14. Comparison: Simulation
Network-Simulator (ns-2)
models MAC layer protocol
use CBR traffic sources (512-Byte data)
Modeling traffic mobility:
random waypoint model
1500 m X 300 m field with 50 nodes
2200 m X 600 m field with 100 nodes

15. Comparison: Results Packet Delivery Fraction
.. As a function of mobility
.. As a function of traffic load

16. Comparison: Results Average end-to-end (data packet) delay
.. As a function of mobility
.. As a function of traffic load

17. Comparison: Results Normalized Routing Load
.. As a function of mobility
.. As a function of traffic load

18. Comparison: Results Normalized MAC load .. As a function of mobility
.. As a function of traffic load

19. Comparison: Results
……now what happens if we increase the load by a LOT…..

20. Conclusions Key differences between the two protocols?
Choice of Routes (congestion metric)
Route Maintenance vs Route Updates
RTS/CTS MAC protocol has implications on dependence on Unicast Packets

21. Discussion
How do the performance characteristics measured by this study relate to sensor networks we have studies?
How realistic are the mobility models (and simulation environment)?

22. Acknowledgements Discussion based on paper:
“Performance Comparison of Two On-Demand Routing Protocols for Ad Hoc Networks”, C. Perkins, E. Royer, S. Das, M. Marina
AODV and DSR animation slides borrowed from: