Dynamic Source Routing (DSR)

Sandeep Gupta

M.Tech - WCC

Overview

Used in multihop wireless ad-hoc networks Completely self-organizing and self-

configuring Completely ‘On-Demand’ Composed of two mechanisms : Route

Discovery & Route Maintenance

Assumptions

All nodes willing to forward packets Diameter of network will often be small ( 5

to 10 hops) Nodes can detect errors & discard packets Nodes move at a moderate speed Unidirectional links may be present Each node has single IP address

Route Discovery

Source checks route cache for route to destination

If no route available, source transmits ROUTE REQUEST

A B C D E“A” “A,B” “A,B,C” “A,B,C,D”

Route Discovery

ROUTE REQUEST gets propagated in the network

When it finally reaches destination, it sends ROUTE REPLY using same or different path

A B C D E“A” “A,B” “A,B,C” “A,B,C,D”

Route Discovery

Destination may piggyback other data like TCP SYN with ROUTE REPLY

A B C D E“A” “A,B” “A,B,C” “A,B,C,D”

Route Maintenance

Each node originating or forwarding a packet confirms receipt of packet by next hop Link Level ack Passive ack Software ack

A B C D E

Route Maintenance

If receipt is not confirmed, ROUTE ERROR is sent to original sender

Sender removes this ‘broken’ link, leaving retransmission to upper layers

A B C D E

Route Maintenance

When retransmitting, sender may use another route to destination in its cache or starts a fresh route discovery

A B C D E

Route Discovery – Additional Features Caching overheard routing information Replying to ROUTE REQUEST using

cached routes ROUTE REQUEST hop limit Preventing ROUTE REPLY storms

Preventing ROUTE REPLY storm

Delay d = H x (h – 1 + r)

h = length of number of hops

r = random no. between 0 & 1

H = small constant delay

A

D C

E F

B G

Route Maintenance – Additional Features Packet salvaging Automatic route shortening (gratuitous

ROUTE REPLY) Piggybacking ROUTE ERROR message

in next ROUTE REQUEST

Support for Heterogeneous Networks & Mobile IP

Each interface is assigned a unique identifier Routes include Node address & interface ID IF_INDEX_MA & IF_INDEX_ROUTER indexes

are used for Mobile IP support

A B C D

1 1 2 4 2

Simulation results50 nodes with 10 active connectionsSimulation length in seconds: 19.49Number of nodes: 50Number of sending nodes: 41Number of receiving nodes: 50Number of generated packets: 2295Number of sent packets: 2283Number of forwarded packets: 0Number of dropped packets: 810Number of lost packets: 0Minimal packet size: 28Maximal packet size: 612Average packet size: 82.5206Number of sent bytes: 231830Number of dropped bytes: 103914

50 nodes with 20 active connectionsSimulation length in seconds: 19.84Number of nodes: 50Number of sending nodes: 47Number of receiving nodes: 50Number of generated packets: 3481Number of sent packets: 3414Number of forwarded packets: 0Number of dropped packets: 1206Number of lost packets: 0Minimal packet size: 28Maximal packet size: 644Average packet size: 83.0361Number of sent bytes: 359450Number of dropped bytes: 135396

Conclusion

“Dynamic Source Routing adapts quickly to routing changes when node movement is frequent, yet requires little or no overhead during periods in which nodes move less frequently. Though DSR overhead increases when traffic is heavy or number of nodes are more but this should still be less compared to distance vector protocols like DSDV where a complete picture of the whole network is present at every node even though it might not require it.”

References

Ad Hoc Networking, Edited by Charles E Perkins, Addison-Wesley

1st sem project report - Simulating IEEE 802.11 with Dynamic Source Routing (DSR) in NS