This document discusses reactive routing protocols in mobile ad hoc networks (MANETs), focusing on the Ad Hoc On-Demand Distance Vector (AODV) protocol. It describes how AODV works by broadcasting Route Request packets when a route is needed, and nodes responding with Route Reply packets if they have a valid route. Intermediate nodes store the address of previous nodes to forward packets. The document outlines the key components of Route Request and Route Reply packets, and notes advantages of AODV such as on-demand route establishment and use of destination sequence numbers, with drawbacks including control overhead and bandwidth consumption from periodic beaconing.

1. Dr.Arun Chokkalingam
Professor
Department of Electronics and Communication
RMK College of Engineering and Technology
Chennai.
UNIT-1- MANET Routing Protocols - Reactive -
Ad hoc On demand Distance Vector Routing- (AODV)

2. Reactive Routing Protocols
› Protocols that fall under this category do not
maintain the network topology information.
› They obtain the necessary path when it is
required, by using a connection establishment
process.
› Hence these protocols do not exchange routing
information periodically.
› Reactive protocols are also known as on
demand routing protocols.
› These protocols find paths to destination only
when needed (on-demand) to transmit a packet.

3. Different Reactive Routing Protocols:
1. Dynamic source routing protocol (DSR);
2. Ad hoc On-demand Distance Vector Routing Protocol
(AODV);
3. Location aided routing (LAR);
4. Associativity-based routing (ABR);
5. Signal stability-based adaptive routing protocol (SSA);

4. Advantages and Shortcomings:
 Lower overhead since routes are determined on demand
 Low storage requirements: only needed routes are in cache.
 High delay of route setup process: routes are established
on-demand;
 Employ flooding (global search)

5. Disadvantages of Dynamic Source Routing (DSR)

6. Differences between AODV and DSR
– In DSR a data packet carries the complete path between
transmitter and receiver
– AODV attempts to improve on DSR by maintaining routing tables
at the nodes, so that data packets do not have to contain
routes
– AODV retains the desirable feature of DSR that routes are
maintained only between nodes which need to communicate
Three steps to establish a path in AODV
1. Route Request Packet (RREQ)
2. Route Reply Packet (RREP)
3. Data Packet

7. Ad Hoc On-demand Distance Vector Routing Protocol
The Route Request (RREQ) packet in AODV carries the
following information:
– The source identifier (srcid): this identifies the source;
– The destination identifier (destid): this identifies the destination
to which the route is required;
– The source sequence number (srcseqnum);
– The destination sequence number (destseqnum): indicates the
freshness of the route.
– The broadcast identifier (bcastid): is used to discard multiple
copies of the same route request.
– The time to live (ttl): this is used to not allow loops.

8. The AODV protocol performs as follows:
› when a node does not have a valid route to destination a Route Request is
forwarded;
› when intermediate node receives a Route Request packet two cases are
possible:
– if it does not have a valid route to destination, the node forwards it;
– if it has a valid route, the node prepares a Route Reply message:
› if the Route Request is received multiple times, the duplicate copies are
discarded:
– are determined comparing BcastID-SrcID pairs.
› when Route Request is forwarded, the address of previous node and its BcastID
are stored;
– are needed to forward packets to the source.
› if Route Reply Packet (RREP) is not received before a time expires, this entry is
deleted
› either destination node or intermediate node responses with valid route;

9. AODV Route Request [RREQ] Packet

10. AODV-Route Reply [RREP]

11. AODV-Advantages and Disadvantages
Advantages
› The main advantage of this protocol is that routes are
established on demand and destination sequence numbers
are used to find the latest route to the destination.
› The connection setup delay is less.
Disadvantages
› Multiple routereply packets in response to a single
routerequest packet can lead to heavy control overhead.
› Another disadvantage of aodv is that the periodic beaconing
leads to unnecessary bandwidth consumption.

12. AODV: Summary
› Routes need not be included in packet headers
› Nodes maintain routing tables containing entries only for
routes that are in active use
› At most one next-hop per destination maintained at each
node
– DSR may maintain several routes for a single destination
› Sequence numbers are used to avoid old/broken routes
› Sequence numbers prevent formation of routing loops
› Unused routes expire even if topology does not change

14. Reference
› https://www.youtube.com/watch?v=wlyibjrHhrs