96 Mobile Computing
6.7 Comparison between DSR and AODV
In this section, we will compare and contrast the routing techniques and mechanisms of DSR
and AODV.
1. General: While DSR and AODV share the on-demand behaviour, many of their routing
mechanisms are very different.
a. DSR uses source routing, whereas AODV uses a table-driven routing framework and desti-
nation sequence numbers.
b. By virtue of source routing, DSR has access to a significantly greater amount of routing
information than AODV. For example, in DSR, by using a single request-reply cycle, the
source can learn routes to each intermediate node on the route in addition to the
intended destination.
c. DSR replies to all requests reaching a destination from a single request cycle. In AODV, on
the other hand, the destination replies only once to the request arriving first and ignores
the rest.
d. The route deletion activity using RERR is also conservative in AODV. By way of active
neighbour list, RERR packets reach all nodes using a failed link on its route to any destina-
tion. In DSR, however, an RERR simply backtracks the data packet that meets a failed link.
Nodes that are not on the upstream route of this data packet, but use the failed link, are
not notified promptly.
Table 6.5 below shows a comparison of the two protocols.
2. Routing overhead: DSR always demonstrates a lower routing overhead than AODV. The
major contribution to routing overhead in AODV is from RERRs, while RREPs constitute a
large fraction of routing overhead in DSR. AODV has more RERRs than DSR, and the con-
verse is true for RREPs.
3. Effect of mobility: Link failures can happen very frequently in MANETs. They trigger new
route discoveries in AODV, since it has at most one route per destination in its routing table.
However, route discovery is delayed in DSR until all cached routes fail. With high mobility,
A
D
F
H
I
B
[A, C]
[A, F]
[A, G]
C
E
G
A
D
F
H
I
B
[I, I]
[I, D]
[I, G]
C
E
G
Figure 6.10(c) RREQ reaches the destination
I. E receives C’s RREQ first, so it accepts C’s
RREQ and discards G’s RREQ.
Figure 6.10(d) I unicasts RREP to G which, in
turn, forwards it to D. A receives RREP from D
and updates its routing table.
Discarded messages
Accepted messa
g
es

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