Dynamic source routing

DSR: The Dynamic Source Routing
Protocol for Multi-Hop Wireless Ad Hoc
Networks
Presenter
Ashraf Uddin
Sujit Singh
South Asian University
(Master of Computer Applications)
http://ashrafsau.blogspot.in/


Routing Overview

 Network with nodes, edges
 Goal: Devise scheme for
transferring message from one
msg
node to another
 Destination routing
 Source routing


Source (“path”) routing

 Source specifies entire route: places complete path to

destination in message header: A – D – F – G

 Intermediate nodes just forward to specified next hop:

D would look at path in header, forward to F

 Like airline travel – get complete set of tickets to final

destination before departing…


Destination (“hop-by-hop”) routing

 Source specifies only destination in message header: G

 Intermediate nodes look at destination in

header, consult internal tables to determine appropriate
next hop

 Like postal service – specify only the final destination on

an envelope, and intermediate post offices select where
to forward next…


Ad Hoc Routing
 Every node participates in routing: no distinction
between “routers” and “end nodes”

 No external network setup: “self-configuring”

 Especially useful when network topology is dynamic
(frequent network changes – links break, nodes come
and go)


Common application
 Mobile wireless hosts
 Only subset within range at

given time

 Want to communicate with

any other node


DSR Protocol Activities
 Route discovery

 Undertaken when source needs a route to a destination

 Route maintenance

 Used when link breaks, rendering specified path

unusable


Route Discovery
• The source sends a broadcast packet which contains
source address, destination address, request id and
path.
• If a host saw the packet before, discards it.
• Otherwise, the route looks up its route caches to
look for a route to destination, If not find, appends its
address into the packet, rebroadcast,
• If finds a route in its route cache, sends a route reply
packet, which is sent to the source by route cache or
the route discovery.


source broadcasts a packet containing address of source and
destination
source (1,4)
1
4

The destination sends a reply packet to source.
8
(1,3) destination
3
7
(1,4,7)
2
The node discards the packets having been seen
(1,2)
6
5
(1,3,5) (1,3,5,6)

The route looks up its route caches to look for a route to destination
If not find, appends its address into the packet

How to send a reply packet
 If the destination has a route to the source in its route
cache, use it

 Else if symmetric links are supported, use the reverse
of route record

 Else if symmetric links are not supported, the
destination initiates route discovery to source


Route Maintenance
 Whenever a node transmits a data packet, a route
reply, or a route error, it must verify that the next
hop correctly receives the packet.
 If not, the node must send a route error to the
node responsible for generating this route header
 Intermediate nodes “eavesdrop”, adjust cached routes
 Source deletes route; tries another if one cached, or
The source restart the route discovery


Route Maintenance……

A B C D E

Route error message: C-D
is broken


DSR Optimization: Route Caching
 Each node caches a new route it learns by any means
 When node S finds route [S,E,F,J,D] to node D, node S
also learns route [S,E,F] to node F
 When node K receives Route Request [S,C,G] destined
for node, node K learns route [K,G,C,S] to node S
 When node F forwards Route Reply RREP
[S,E,F,J,D], node F learns route [F,J,D] to node D
 When node E forwards Data [S,E,F,J,D] it learns route
[E,F,J,D] to node D
 A node may also learn a route when it overhears Data

Additional Route Discovery features

DSR route discovery does not allow nodes like F to
reply to RREQ



Node C may infer
 Preventing Route Reply that the initiator has
already received a h=2
storms
Route Reply giving
 Many Route Reply message C
a better route
could be send to A from the because the data
A’s neighbors packet received
 To avoid a possible local from B contains a
congestion, each nodes must value of “h” less
wait a variable period before than its h’s value
A B G
sending the reply.
 Delay period d = H(h - 1 + r) h=1
 Each node network interfaces
works into “promiscuous” E
receive mode.
h=3


 Route request Hop limits
 “Nonpropagating” Route Request(hop lim 0)
 To determine if the target is
2 Hop limit
neighbour or a neighbour has a route
1 Hop limit
to the target cached.
 “Propagating” Route Request( no hop lim) Non
Propagating
 If no route reply is recived after a Route
Request The expanding ring search
approach can carry to the
short timeout. average latency increasing

 “Expanding ring”
 Increase hop value stepwise if no
route reply is recieved.


Additional Route Maintenance features


Support for Heterogeneous networks & mobile IP

 Heteregenous network :
Different kind of devices with different interfaces.
Possibly , multiple interfaces( short range & long range)


DSR evaluation
 Simulation
 To analyse the behavior and performance of DSR.
 To Compare with other routing protocols
 Set Up:
 Ad hoc of 50 mobiles nodes
 15 minutes ( 900 seconds) simulation time.
 CBR data traffic
 20 mobile nodes traffic sources; 4 packets/sec.
 Random waypoint mobility model ( pause time)


Packet Delivery Ratio(with movement speed 1m/s)


Routing Overhead(with movement speed 1m/s)


Packet Delivery Ratio(with movement speed 20m/s)


Routing Overhead(with movement speed 20m/s)


RESULT
 At both movement speeds, DSR delivers almost all
data packets, regardless of pause time.
 100% delivery ratio at pause time 900 sec, a stationary
network.
 At 1 m/s delivery ratio> 99.5%
 At 20 m/s delivery ratio> 98%


Advantages
 Routes maintain only between nodes who need to
communicate. Reduces overhead of routing
maintenance.
 route caching reduces route discovery overhead.
 A single route may yield many routes to the
destination.


Disadvantages

 Packet header size grows with route length due to
source routing.
 Flood route request may potentially reach all nodes in
the network.
 Route reply storm problem.


Conclusion

 Excellent performance for routing in multi-hop ad hoc.
 Very low routing overhead.
 Able to deliver almost all originated data packets, even
with rapid motion of all nodes.


THANKS


Reference
[1]. David B. Johnson, David A. Maltz, and Josh
Broch, "DSR: The Dynamic Source Routing Protocol
for Multi-Hop Wireless Ad Hoc Networks", in Ad Hoc
Networking, edited by Charles
E. Perkins, Chapter 5, pp. 139-172, Addison-
Wesley, 2001. Invited paper.


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