A comparison of Ad-Hoc Routing Protocols
Alvin AuYoungCSE 291-B
April 24, 2003
A Review of Routing
Route discovery how do I get from source to destination?
Stored route state what route bookkeeping is involved?
Route update
how do I find out if a route has changed?
Route decision/metric
how do I choose which path to follow?
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
Issues in Wireless Networks
Channel Access/Availability
Hidden terminal problem
Issues in Ad-hoc Networks
Host mobility
Lack of infrastructure
Unpredictable network topology
Power limitations
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
On-demand Routing Protocols
Routes are created by some route discovery
mechanism “on demand”
Up-to-date Route information is not actively propagated
Ad-Hoc Routing Protocols
AODV
Ad-hoc On-demand Distance Vector Protocol
DSR
Dynamic Source Routing
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
The node discards the packets having been seen
source
destination
The source broadcasts a route packetThe neighbors in turn broadcast the packet till it reaches the destination
Reply packet follows the reverse path of route request packet recorded in broadcast packet
RREQ
RREP
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.
destination
source1
65
4
3
2
8
7
(1,4)
(1,2)
(1,3)
(1,3,5,6)(1,3,5)
(1,4,7)
source broadcasts a packet containing address of source and destination
The route looks up its route caches to look for a route to destinationIf not find, appends its address into the packet
The destination sends a reply packet to source.
The node discards the packets having been seen
Comparison: Goals
Packet Delivery Fraction
End-to-end Delay of Data Packets
Normalized Routing load
Normalized MAC load
Comparison: Simulation
Network-Simulator (ns-2)
models 802.11 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
Comparison: Results
Packet Delivery Fraction
.. As a function of mobility
.. As a function of traffic load
Comparison: Results
Average end-to-end (data packet) delay
.. As a function of mobility
.. As a function of traffic load
Comparison: Results
Normalized Routing Load
.. As a function of mobility
.. As a function of traffic load
Comparison: Results
Normalized MAC load
.. As a function of mobility
.. As a function of traffic load
Comparison: Results
……now what happens if we increase the load by a LOT…..
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
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)?
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: http://www.cs.buffalo.edu/~qiao/cse620/ad_hoc_2001.ppt