Routing Protocols of On- Demand Dynamic Source Routing (DSR) Ad-Hoc On-Demand Distance Vector (AODV)

Outline DSR Introduction Route Discovery Route Maintenance AODV Introduction Route Discovery Route Maintenance Comparison

Dynamic Source Routing (DSR) Route Cache A packet carries the list of routers in the path Two main operation Route Discovery Route Maintenance No periodic messages

DSR Assumptions Small network diameter Speed of mobility is moderate Choice of promiscuous receive mode Links may or may not be bi-directional

DSR Route Discovery RREQ (Route Request) [Initiator, Target, Request id, Path] RREP (Route Reply) Target sends ROUTE REPLY if it knows route to sender Target initiates ROUTE REQUEST to sender and piggybacks the ROUTE REPLY to avoid infinite recursion Target uses the reverse route from the recorded route RRER (Route Error)

DSR Route Discovery A B C D EG F H [A,G,ID,A] [A,G,ID,AB] [A,G,ID,ABE] [A,G,ID,AC] Node E drop the packet because it has forward the same ID packet Source A forward data to destination G

DSR Route Reply A B C D EG F H [A,B,E] Node A stores the route from A to G in its route cache

DSR Route Maintenance Use low-level acknowledgements to detect broken links; inform sender via route error packet If no route to the source exists Use piggybacking Send out a route request and buffer route error Sender truncates all routes which use nodes mentioned in route error Initiate route discovery

DSR Route Error A B C D EG F H E sends a route error to A along route E-B-A RERR [E-G] Nodes hearing RERR update their route cache to remove link E-G

Optimizations for efficiency Route Cache Store the recent information Each forwarding host can add route information to cache All source routes learned by a node are kept in Route cache reduces cost of route discovery

Optimizations for efficiency ABCD Step1: Discovery A->D E Step2: Discovery A->E Step3: Discovery, find A->C only single host BCD CE CD CE

Optimizations for efficiency Piggybacking Data is piggybacked on Route Request Packet and Route Reply Packet Reflecting shorter routes ABCD BCDCD

DSR Advantages Routes maintained only between nodes who need to communicate reduces overhead of route maintenance Route caching can further reduce route discovery overhead

DSR Disadvantages Packet header size grows with route length due to source routing Flood of route requests may potentially reach all nodes in the network Care must be taken to avoid collisions between route requests propagated by neighboring nodes

Ad-hoc On-demand Distance Vector (AODV) Improved over DSDV algorithm minimize the number of required broadcast by creating routes on a demand basis AODV retains the desirable feature of DSR that routes are maintained only between nodes which need to communicate DSR resulting large headers can sometimes degrade performance Nodes (not on a selected path) don’t maintain routing information or participate in routing table exchanges. AODV uses sequence numbers

AODV Route table entry Destination Next hop Number of hops (metric) Sequence number for the destination Active neighbors for this route Expiration time for the route table entry

AODV RREQ Route Requests (RREQ) are forwarded in a manner similar to DSR A node re-broadcasts a Route Request, it sets up a reverse path pointing towards the source

AODV RREP Route Reply travels along the reverse path set-up when Route Request is forwarded RERR (Route Error) Periodic forward messages to detect link Hello Message Neighboring nodes periodically exchange hello message

AODV Route Discovery A B C D EG F H Source A forward data to destination G A broadcast RREQ sets up a reverse path

AODV Route Discovery A B C D EG F H

A B C D EG F H

AODV Route RREP A B C D EG F H

AODV Reverse Path Reverse path setup Forward RREP Destination IP address Source IP address Broadcast_id Expiration time for reverse path route entry Source node ’ s sequence number

DSR VS AODV Difference DSR forward greater packets than AODV AODV periodically forward Hello Message to neighbors, DSR not. Similarity Node (not on a select path) do not maintain routing information Only forward the first copy packet RREQ, RREP, RRER

Reference D. B. Johnson and D. A. Maltz. “ Dynamic Source Routing in Ad Hoc Wireless Networks ”,1996 C. E. Perkins, E. RM. Royer, and Samir R. Das. “ Ad Hoc On-Demand Distance Vector ”,2000