1. 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/
http://ashrafsau.blogspot.in/
2. Routing Overview
Network with nodes, edges
Goal: Devise scheme for
transferring message from one
msg
node to another
Destination routing
Source routing
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3. 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…
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4. 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…
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5. 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)
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6. Common application
Mobile wireless hosts
Only subset within range at
given time
Want to communicate with
any other node
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7. DSR Protocol Activities
Route discovery
Undertaken when source needs a route to a destination
Route maintenance
Used when link breaks, rendering specified path
unusable
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8. 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.
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9. 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
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10. 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
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11. 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
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12. Route Maintenance……
A B C D E
Route error message: C-D
is broken
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13. 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
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14. Additional Route Discovery features
DSR route discovery does not allow nodes like F to
reply to RREQ
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17. Additional Route Discovery features
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
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18. Additional Route Discovery features
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.
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23. Support for Heterogeneous networks & mobile IP
Heteregenous network :
Different kind of devices with different interfaces.
Possibly , multiple interfaces( short range & long range)
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24. 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)
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29. 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%
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30. 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.
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31. 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.
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32. 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.
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34. 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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