A comparison of Ad-Hoc Routing Protocols Alvin AuYoung CSE 291-B April 24, 2003
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?
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 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
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.
source broadcasts a packet containing address of source and destination source (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
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