Mobile adhoc

A Paper Presentation on
ROUTING PROTOCOLS
IN MOBILE AD HOC NETWORKS
(MANETS)
Prepared For
SAMYAK’09
K L E F UNIVERSITY
Vijaywada.
Presented by,
M.Pavan K.Hari Prasad
gettopavan@gmail.com hari1219@gmail.com
IVth IT IVth IT
Ph.No:9490017034 Ph.No:9492757194
MALINENI LAKSHMAIAH ENGINEERING COLLEGE
(Affiliated to JNTU, Kakinada and Approved by AICTE)
(Accredited by NBA)
Singarayakonda, PRAKASAM Dt. - 523101

Routing Protocols in Mobile Ad Hoc Networks – MANETs
Abstract:
A mobile ad hoc network
(MANET) is a wireless network that
uses multi-hop peer-to-peer routing
instead of static network infrastructure to
provide network connectivity. Ad-Hoc
networks are mobile wireless networks
that have no fixed infrastructure. There
are no fixed routers- instead each node
acts as router and forwards traffic from
other nodes. MANET is a type of ad-hoc
network with rapidly changing topology.
Since the nodes in a MANET are highly
mobile, the topology changes frequently
and the nodes are dynamically connected
in an arbitrary manner. In order To
facilitate communication with the
network, a routing protocol is used to
discover the routes between nodes.
Efficient routing of packet is a primary
MANET challenge. Today, there exist
various routing protocols for this
environment.
Mobile Ad Hoc Networks
(MANETs) consist of nodes that change
position frequently. To accommodate the
changing topology special routing
algorithms are needed. For relatively
small networks flat routing protocols
may be sufficient. However, in larger
networks either hierarchical or
geographic routing protocols are needed.
There is no single protocol that fits all
networks perfectly. The protocols have
to be chosen according to network
characteristics, such as density, size and
the mobility of the nodes.
MANETs have applications in
rapidly deployed and dynamic military
and civilian systems. The network
topology in a MANET usually changes
with time. Therefore, there are new
challenges for routing protocols in
MANETs since traditional routing
protocols may not be suitable for
MANETs. For example, some
assumptions used by these protocols are
not valid in MANETs or some protocols
cannot efficiently handle topology
changes.
Current research on routing
protocols for Mobile Ad-hoc Network
(MANET) has converged to several
dominating routing protocols, including
Optimized Link State Routing (OLSR),
Ad-hoc On-demand Distance Vector
(AODV) and Dynamic Source Routing
(DSR). At the same time, classic routing
protocols such as Open Shortest Path
First (OSPF) and Destination Sequenced
Distance Vector (DSDV) are improved
for the MANET context. Research
efforts also focus on issues such as
Quality of Service (QoS), energy
efficiency, and security, which already
exist in the wired networks and are
worsened in MANET.
This paper gives brief description on
what are Mobile Ad Hoc NETworks,
what are their uses, routing protocols in
MANETs, and various types of protocols
that are available for the MANETS.
Finally after a brief description of the
protocols there is a comparison
simulation that describes which protocol
is suited under which circumstances.
2

Introduction:
The Internet Engineering Task Force
has defined a Mobile Ad hoc Network
(MANET) as:
“An autonomous system of mobile
routers (and associated hosts) connected
by wireless links--the union of which form
an arbitrary graph. The routers are free to
move randomly and organize themselves
arbitrarily; thus, the network's wireless
topology may change rapidly and
unpredictably. Such a network may
operate in a standalone fashion, or may be
connected to the larger Internet”.
Simply put, a MANET is a wireless
mobile network that is self-forming, self
maintained, and self-healing. Nodes stay
connected even as the network topology
changes.
The Mobile Ad hoc network is a
collection of wireless mobile hosts
forming a temporary network without the
aid of any established infrastructure or
centralized administration. In such an
environment, it may be necessary for one
mobile host to enlist the aid of other hosts
in forwarding a packet to its destination,
due to the limited range of each mobile
host’s wireless transmissions. In order to
make that work, typically each node needs
to act as a router to relay packets to nodes
out of direct communication range. Under
these circumstances, routing is much more
complex than in conventional (static)
networks. Many of the possible solutions
are determined by the characteristics of the
media, the behavior of nodes and the data
flow. Since research in Ad Hoc
Networking has resulted in such a large
amount of routing algorithms and
protocols, it has become more and more
difficult to decide, which algorithms are
superior to others under what conditions.
For a successful deployment, this is an
important problem, since a wrong choice
may have a severe impact on the
performance, and consequently on the
acceptance of the new technology. Also,
providing just any protocol is not feasible,
due to the different requirements on
hardware and lower network layers.
What are Mobile Ad-Hoc
Networks?
Mobile Ad-Hoc Networks
(MANETs) are collections of mobile
nodes, dynamically forming a temporary
network without preexisting network
infrastructure or centralized
administration.
• Mobile nodes can be arbitrarely located
and are free to move randomly at any
given time.
• No dedicated routers, each node in a
MANET network acts as a router and is
responsible for discovering and
maintaining routes to other nodes.
• The primary goal of the MANET routing
protocol is correct and efficient route
establishment to facilitate communication
within the network between arbitrary
nodes.
Where MANETs are used?
• For military and rescue use.
• Information distribution for meetings,
seminars etc.
• Internet / intranet hot spots in public
transportation.
• Localized advertising and shopping.
• New mobile devices are invented
constantly and used various ways.
Characteristics of MANET
3

networks:
• Dynamic topology: Nodes are free
to move arbitrarely within the
network (or leave and join the
network) causing random topology
changes which can happen rapidly
at unpredictable times.
• Variable capacity links:
Significantly lower link capacities
compared to traditional hardwired
links.
• Energy-constrained mobile nodes:
Nodes usually operate on batteries
a all operations must be optimized
for energy conservation.
• Weakened physical security: More
prone to physical threats than
hardwired networks.
Why traditional routing protocols
are not suitable for MANETs?
• MANETs are usually highly dynamic
and heterogeneous mobile networks.
• No pre-existing infrastructure.
• No centralized administration.
• Dynamic topologies.
• Variable capacity links.
• Energy-constrained nodes.
• Limited physical security.
MANET Protocols:
Some of the better known MANET
protocols are AODV, TORA, DSR,
TBRPF and OLSR. Each protocol has
evolved over time to better suit the
particular requirements of various types of
mobile ad hoc networks.
These protocols are classified
broadly into two categories.
1) Proactive
2) Reactive.
These two protocols suffer from
some problems under some situations. So
there are new types of protocols developed
which combine the features of both the
proactive and reactive types
]Reactive vs. proactive ad-hoc
routing protocols:
Proactive Protocols:
Periodic topology updates a node
always possesses the latest routing
information.
Proactive MANET protocols update
routing information in a proactive manner
by exchanging route information at
periodic intervals. The exchange of table-
based route information is evenly
distributed across the wireless network. As
a result, routes are established prior to
being needed, providing a wireless
network that is low in latency, at the
expense of increased overhead.
The well known proactive routing
protocols are TBRPF, DSDV.
Reactive protocols:
Rather than distribute all route
information across the entire network, On-
demand MANET protocols perform route
maintenance only when required. On-
demand protocols create fewer networks
overhead since the exchange of routing
information is localized rather than evenly
distributed. The result is a network with
less overhead, at the expense of increased
latency due to the route discovery process
The well-known reactive protocols
are AODV, DSR.
DSR AODV TBRPF DSDV
4
Ad-Hoc Routing Protocols
ProactiveReactive

A
Now let us know about each of these
MANET protocols.
Reactive Routing Protocol-DSR:
The acronym for DSR is Dynamic
Source Routing.
 The DSR is a simple and efficient
on-demand source routing protocol
designed for multihop wireless ad-
hoc networks.
 Two major phases: route discovery
and route maintenance.
 Route discovery = used to discover
new source routes across multiple
network hops to arbitrary
destinations in an ad-hoc network.
 Route maintenance = responsible
for detecting network topology
changes and keeping up-to-date
information of already discovered
source routes.
 Route discovery and route
maintenance rely on source route
caches and they can contain several
routes to the same destination
node.
 Designed to work up to 200 nodes.
 Supports both unidirectional and
bidirectional links.
Route Discovery:
Route Req.
“A” “A, B” “A, B, C”
id=2 id=2 id=2
Initiator Target
Route Reply
“A, B, C”
id=2
 If source route to the target node is
not found from the cache node A
initiates route discovery.
 Route-Request packet contains:
- Information about initiator (A)
- The target of Route-Request (E)
- Unique request identifier (2)
- List of node addresses through
which the particular Route-
reqest has been forwarded.
 It is highly possible that some
nodes receive the same Route-
Request packet more than once
duplicate packets are discarded.
 When returning Route-Reply, node
E must take into account that some
links in source route might be
unidirectional (MAC).
 If node E doesn’t have a route to
node A, it must it turn send a
Route-Request to the node A. In
that case, Route-Reply packet is
piggybacked in a Route-Request
packet to avoid infinite recursion.
Route Maintainance:
 Each node is responsible for
confirming that the next hop in a
source route receives the packet.
 The packet is retransmitted up to
some maximum number of times
until the confirmation is received
from the next hop.
 Route-Error packet contains
information which link has failed
so the initiator can remove that
source route from its cache.
 When a node receives a Route-
Request, it first searches its route
cache for the target node. If route is
found, the node can send a Route-
Reply to the initiator.
5
B C D

A
A
Preventing Route-Reply storms:
 Cache lookups allow nodes to
quickly reply to Route-Requests
but can result Route-Reply storms.
 To avoid storms, the DSR uses a
random delay before a node can
send a Route-Reply.
 d = H * (h – 1 + r)
- H, small const. Delay
- h, number of hops is source
route
- r, 0 or 1
Longest source routes are send last.
HOP Limits:
 A Route-Request packet contains a
hop limit which can be used to
limit the number of intermediate
nodes participating in the route
discovery.
 The hop limit can be used to
implement an expanding ring type
of route discovery technique.
Packet salvaging:
Initiator Target
 When a route error is detected and
the Route-Error packet has been
sent, a node may attempt to salvage
data packet instead of discarding it.
 If the node which sent the Route-
Error packet finds a new route to
the target node from its route
cache, it can replace the original
source route with the new one.
 After replacing the original source
route, the data packet is marked as
salvaged to prevent the packet
being salvaged multiple times
which might result routing loop.
Automatic Route Shortening:
 Source routes in use may be
automatically shortened if one or
more intermediate nodes are no
longer needed.
 The node which notices that there
are redundant intermediate nodes
in path, sends a Route-Reply to the
initiator which contains shortened
route to the target node.
Use of Route-Error Messages:
 When an initiator node receives a
Route-Error packet, it piggybacks
this error message to the next
Route-Request and broadcasts it to
the local network.
 In this way, the route caches of
adjacent nodes will be cleaned up
from invalid routes.
Multicast routing:
 DSR does not support true
multicasting but provides some
means to simulate it.
 When a DSR node wants to send a
multicast data packet, it
piggybacks it inside a Route-
Request packet which target
address is set to some specified
multicast address.
 The Route-Request packet is then
broadcasted normally within the
specified hop count.
 Different hop count values allow
nodes to use controlled ring like
flooding.
Reactive Protocol-AODV :
The Ad hoc On-Demand Distance
Vector (AODV) is an embedded MANET
protocol that works dynamically to
6
B C D
B C D

establish and maintain routes, adapting
quickly to changing link conditions. The
Ad hoc On-Demand Distance Vector
(AODV) algorithm enables dynamic, self-
starting, multihop routing between
participating mobile nodes wishing to
establish and maintain an ad hoc network.
AODV allows mobile nodes to obtain
routes quickly for new destinations, and
does not require nodes to maintain routes
to destinations that are not in active
communication. AODV allows mobile
nodes to respond to link breakages and
changes in network topology in a timely
manner.
The operation of AODV is loop-
free, and by avoiding the Bellman-Ford
"counting to infinity" problem offers quick
convergence when the ad hoc network
topology changes (typically, when a node
moves in the network). When links break,
AODV causes the affected set of nodes to
be notified so that they are able to
invalidate the routes using the lost link.
One distinguishing feature of AODV
is its use of a destination sequence number
for each route entry. The destination
sequence number is created by the
destination to be included along with any
route information it sends to requesting
nodes.Using destination sequence numbers
ensures loop freedom and is simple to
program. Given the choice between two
routes to a destination, a requesting node
is required to select the one with the
greatest sequence number.
Messages for route discovery:
Route Requests (RREQs), Route
Replies (RREPs), and Route Errors
(RERRs) are the message types defined by
AODV. These message types are received
via UDP, and normal IP header processing
applies.
The messages are not blindly
forwarded. However, AODV operation
does require certain messages (e.g.,
RREQ) to be disseminated widely, perhaps
throughout the ad hoc network. The range
of dissemination of such RREQs is
indicated by the TTL in the IP header.
Fragmentation is typically not required.
Route Creation:
When a source node does not have a
route for a required destination, AODV
initiates a route request/route reply cycle
by broadcasting a route request (RREQ)
packet across the wireless network. Upon
receiving the RREQ, nodes must
determine whether or not they are the
destination node. If a node is not the
destination and does not have a route to
the destination, it will rebroadcast the
RREQ to its neighbors and update its route
table to include a reverse pointer to the
source node. This process will continue
until a route to the destination node is
found, or the If a node is the destination
node, or has a route to the destination
node, it will respond by sending a route
reply (RREP) to the source node.
Intermediate nodes update their route
information about the source and
destination nodes. Upon receiving the
RREP, the source node can forward data to
the destination node using the newly
created route. If the RREP is not received
within a certain time frame, the source
node will retry the RREQ. route request
process times out.
Route Deletion:
A route will remain active as long as
data continues to travel across the route. If
a route becomes inactive for a period of
time, the route will be deleted. A
userdefined timeout value determines the
time period for which a route must be
inactive in order to be deleted from the
route table. Each time a packet is sent
across a route, the timer is reset. Any time
a link breakage occurs, a route error
7

(RERR) is propagated to mark the
unusable route as invalid. Upon detecting
a broken link, a node will send a RERR to
any neighbors that had been using the
node as the next hop for the route. After
receiving the RERR, each node deletes the
invalid route from its route table. If a route
to the destination is still required, the
source node will reinitiate the route
discovery process. ERR packets are not
sent if the route timeout expires, as all
intermediate routers will have timed out as
well.
Sequence Numbers:
AODV uses sequence numbers to
avoid routing loops and to measure the
“freshness” of route information. Prior to
broadcasting RREQ, RREP, and RERR
packets, AODV must increment its
sequence number. Each route maintains a
sequence number, with higher sequence
numbers indicating “fresher” routes. When
multiple routes are available to a
destination node, the route with the
greatest sequence number is used. Packets
with lower sequence numbers are ignored
and dropped.
Stationary Wireless Infrastructure:
While many mobile ad hoc networks
do not rely on any stationary
infrastructure, many applications require
the use of towers/repeaters to extend the
range of the wireless network. While using
stationary infrastructure provides a more
cellular like wireless network, this type of
infrastructure can create issues that
MANET protocols do not typically take
into account.
The network uses towers to extend
the range of wireless network. The towers
have strong signals between them. All
application data from the mobile vehicles
is sent to the wired network connected at
tower.
At some point, the signal to Tower A
has become too weak for application data
to successfully traverse the network. The
signal between the vehicle and Tower A is
barely strong enough for the AODV
control messages to reach Tower A. If
enough control messages are received
between the vehicle and the tower, Tower
A may remain listed as a viable route to
the network to which it is connected. The
vehicle now has a strong link to Tower B,
which in turn has a strong link to Tower A.
Tower A will remain listed as a
viable gateway to the network as long as
the vehicle receives the minimum amount
of control messages required to keep a
route in the route table. Once the vehicle
gets completely out of range from Tower
A, Tower B will become the intermediate
node. This issue is commonly known as
“Gray Zone.”
To combat the Gray Zone issue it
accounts for control packet signal strength
information when making routing
decisions. Embedded within each control
packet is a signal strength measurement.
The control packet contains a user-defined
signal strength threshold. If the control
packet signal strength from Tower A falls
below the user-defined threshold, the
vehicle’s direct route to Tower A will be
dropped, forcing the vehicle data to find a
new route. As a result, the vehicle would
route data to Tower A by using Tower B
as an intermediate node. Even though this
creates an extra hop for the route, the route
is more efficient since the signal remains
strong.
Proactive Routing Protocol-DSDV
The acronym for DSDV is Distance
Vector Destination Sequenced Routing.
This routing protocol was developed at the
IBM, in 1996. The protocol is a distance
vector protocol, which uses the modified
Bellman-Ford algorithm. This is a
8

Proactive Routing protocol, where the
route is always available. However, the
protocol has some limitations as well. It
maintains routing info among all the
nodes, it uses periodic update messages,
there is a route settling time and routes
may not converge.
The DSDV protocol operates in the
following way:
Mobile nodes maintain routes to all
possible destinations and exchange routing
information between each other. Hop
counts are used as routing metrics, and in
order to ensure that the routing
information is up to date, sequence
numbers are used. A given node keeps
track of its own time and the sequence of
events that happen. Thus, the node assigns
sequence numbers to distance vector
updates, which updates contain
information about the neighbors.
Proactive Routing Protocol-
TBRPF:
Topology Dissemination Based on
Reverse-Path Forwarding (TBRPF) is a
proactive, link-state routing protocol
designed for mobile ad-hoc networks
(MANETs), which provides hop-by-hop
routing along shortest paths to each
destination. Each node running TBRPF
computes a source tree (providing shortest
paths to all reachable nodes) based on
partial topology information stored in its
topology table, using a modification of
Dijkstra's algorithm. To minimize
overhead, each node reports only part of
its source tree to neighbors.
TBRPF uses a combination of
periodic and differential updates to keep
all neighbors informed of the reported part
of its source tree. Each node also has the
option to report addition topology
information (up to the full topology), to
provide improved robustness in highly
mobile networks
TBRPF performs neighbor discovery
using "differential" HELLO messages
which report only changes in the status of
neighbors. This results in HELLO
messages that are much smaller than those
of other link-state routing protocols such
as OSPF.
TBRPF consists of two main
modules: the neighbor discovery module,
and the routing module which performs
topology discovery and route computation.
Neighbor Discovery:
The TBRPF Neighbor Discovery
(TND) protocol allows each node i to
quickly detect the neighbor nodes j such
that a bidirectional link (I,J) exists
between an interface I of node i and an
interface J of node j. The protocol also
quickly detects when a bidirectional link
breaks or becomes unidirectional. TND is
designed to be fully modular and
independent of the routing module. TND
performs ONLY neighbor sensing, i.e., it
determines which nodes are (1-hop)
neighbors. As a result, TND can be used
by other routing protocols, and TBRPF
can use another neighbor discovery
protocol in place of TND, e.g., one
provided by the link layer.
Nodes with multiple interfaces run
TND separately on each interface, similar
to OSPF. Thus, a neighbor table is
maintained for each local interface, and a
HELLO sent on a particular interface
contains only information regarding
neighbors heard on that interface.
Advantages of modular neighbor
sensing:
• If a network performs neighbor
sensing in the link/mac layer, then
TBRPF can be used without
HELLOs, thus eliminating
redundancy.
9

• TBRPF neighbor sensing can be
used with other routing protocols,
and conversely, other neighbor
sensing protocols can be used with
TBRPF.
• In OLSR, since HELLOs (which
report neighbor interface
addresses) are used to discover 2-
hop neighbors, MPRs cover all 2-
hop interfaces, which is redundant.
• In TBRPF, 2-hop neighbors are
discovered using Topology
Updates (not HELLOs), so parent
selection is based only on Router
IDs thus avoiding this redundancy.
Routing Module:
Each node running TBRPF maintains
a source tree, denoted T, which provides
shortest paths to all reachable nodes. Each
node computes and updates its source tree
based on partial topology information
stored in its topology table, using a
modification of Dijkstra's algorithm. To
minimize overhead, each node reports only
part of its source tree to neighbors. The
main idea behind the current version of
TBRPF came from PTSP, another protocol
in which each node reports only part of its
source tree.
The part of T that a node reports to
neighbors is called the "reported subtree"
and is denoted RT. Each node reports RT
to neighbors in periodic topology updates
(e.g., every 5 seconds), and reports
changes (additions and deletions) to RT in
more frequent differential updates (e.g.,
every 1 second). Periodic updates inform
new neighbors of RT, and ensure that each
neighbor eventually learns RT even if it
does not receive all updates. Differential
updates ensure the fast propagation of each
topology update to all nodes that are
affected by the update. A received
topology update is not forwarded, but may
result in a change to RT, which will be
reported in the next differential or periodic
update.
Comparison Simulations:
Features of protocols:
AODV DSR TBRPF
Loop-freedom Yes Yes No
Multiple routes No Yes Possible
Unidirectional
link support
Possible Yes No
Multicast Possible No No
Periodic
Broadcast
Possible No Yes
Maximum No.
of nodes
<100 200 <200
Expiration of
routing info.
Yes No Yes
Category Reactive Reactive Proactive
Metrics used in the studies:
_ Packet delivery ratio: Ratio between
the amount of incoming and actually
received application data packets
_ Routing overhead: Total number of
routing control packets transmitted during
the simulation
_ Control byte overhead: Total number
of routing control bytes used in the control
packets
_ Path optimality: Difference between
the actually taken and the best possible
path for a packet to reach its destination
Summarizing the results:
Low mobility, low traffic
AODV DSR TBRPF
Packet
delivery
ratio
High High High
End to end
delay
Middle Middle Middle
Routing Low Low Middle
10

overhead
Path
optimality
Middle Middle Very
good
High mobility, High traffic
AODV DSR TBRPF
Packet
delivery
ratio
Middle Middle High
End to end
delay
Middle Middle Middle
Routing
overhead
Very
High
Middle Middle
Path
optimality
Middle Low Good
_ The routing overhead for the two on-
demand protocols heavily depends on
node mobility
_ In general, AODV sends many small
routing control packets, while DSR sends
less, but bigger control packets (this also
depends on the used data packet size)
_ Some of the authors consider DSR more
useful in smaller networks with less
mobility and the usage of AODV more
appropriate in ad-hoc networks with a
higher mobility and data transfer rate.
_ TBRPF has a constant routing overhead
(proactive)
_ All protocols do quite well concerning
delivery ratio
Problems of the particular protocols:
_ AODV uses more, but smaller routing
control packets  critical concerning
wireless medium properties (e.g.
interference). This becomes worse for a
higher load, as neighbors have to be
rediscovered (congestion causes link
failures).
_ DSR has some problems concerning the
cache usage: The advantage of multiple
routes becomes a disadvantage with high
mobility (lack of good criteria for
choosing one particular of the possible
routes). In bigger networks, the source-
routing principle can also become a
problem.
_ TBRPF is a proactive protocol.
Therefore it may not be suitable for
networks with low mobility (e.g.
stationary battery powered sensor
networks). The lack of loop-freedom
causes packet loss, waste of bandwidth
and causes other problems.
Conclusion:
To improve efficiency, it is essential
to model the performance of existing
protocols. In order to do so, we have
compared the performance of Proactive
(TBRPF) and Reactive (ADOV and DSR)
routing protocols for mobile ad hoc
networks in terms of Throughput and End
to End Delay.
It was observed from simulation that
DSDV gives maximum throughput in
small sized networks, DSR for Medium
sized networks and ADOV for large
networks.
Although hardware integration and
wireless communication devices have
improved in the last few years, .the. Ad-
hoc routing protocol has not yet been
found.
- The recent activities of the MANET
working group show that there are still
fundamental questions to answer.
. Scalability?
. Energy efficiency?
. Security?
. Combination of physical, data-link and
network layer?
- MANET hopes that experiences made
with third-party experimental
implementations helps solving them.
- Additionally, more fundamental research
is done by the IRTF.
References:
Websites:
-- http://www.ietf.org/rfc/rfc3561.txt
11

-- http://www.isi.edu/
-- http://www.cs.technion.ac.il/
Books:
-- Bertsekas, D. and R. Gallager, "Data
Networks, Prentice-Hall", 1987
.
12

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