The document discusses ad hoc networks. It defines an ad hoc network as a temporary network connection between devices without fixed infrastructure. Key characteristics of ad hoc networks include dynamic topology, nodes that can freely join and leave, multi-hop routing, and limited bandwidth. The document compares ad hoc networks to wired and managed wireless networks. It also discusses different types of ad hoc networks and routing protocols like DSR and AODV. Applications of ad hoc networks include military operations, conferences, and emergency response situations.

1. 1
Ad Hoc Networks
By Shashi Gurung
Assistant Professor
CTIEMT

2. Ad Hoc Networks
2
 An ad hoc network is a temporary connection
between computers and devices used for a
specific purpose, such as sharing documents
during a meeting or playing multiplayer computer
games.
 An ad hoc network is made up of multiple “nodes”
connected by “links.”

3. Characteristics
3
 No fixed infrastructure
 Auto-configurable network and Self organizing
 Dynamic changing topology
 Mobile devices join/leave the network unexpectedly;
they can also move freely
 Energy-constrained-limited energy
 Limited bandwidth
 Autonomous-
- Each node also serves as router
 Help to relay packets received from neighbors
 Multihop Communication

4. 4
 1)Distributed operation: There is no background network for the central control of the network
operations, the control of the network is distributed among the nodes. The nodes involved in a
adhoc should cooperate with each other and communicate among themselves and each node
acts as a relay as needed, to implement specific functions such as routing and security.
 2) Multi hop routing: When a node tries to send information to other nodes which is out of its
communication range, the packet should be forwarded via one or more intermediate nodes.
 3) Autonomous terminal: In adhoc, each mobile node is an independent node, which could
function as both a host and a router.
 4) Dynamic topology: Nodes are free to move arbitrarily with different speeds; thus, the network
topology may change randomly and at unpredictable time. The nodes in the MANET dynamically
establish routing among themselves as they travel around, establishing their own network.
 5) Light-weight terminals: In maximum cases, the nodes at adhoc are mobile with less CPU
capability, low power storage and small memory size.
 6) No infrastructure: The adhoc network is infrasctureless network which means they are not
depended on any infrastructure.
 7) Dynamic changing topology
 Mobile devices join/leave the network unexpectedly; they can also move freely
8)-Energy Constraint-Limited energy because of dependent on battery.

5. Comparison
5
 ADHOC vs. Wired networks
 In MANETs, each node also works as router for
forwarding packets
 In wired networks, routers perform routing task
 ADHOCs vs. Managed wireless networks
 No infrastructure in MANETs
 Special node known as access point (AP) in managed
wireless networks

6. 6

7. 7
 Applications
 Military arena: An ad hoc networking will allow the military battleground to
maintain an information network among the soldiers, vehicles and headquarters
 Provincial level: Ad hoc networks can build instant link between multimedia
network using notebook computers or palmtop computers to spread and share
information among participants (e.g. Conferences).
 Personal area network: A personal area network is a short range, localized
network where nodes are usually associated with a given range.
 Industry sector: Ad hoc network is widely used for commercial applications.
Ad hoc network can also be used in emergency situation such as disaster relief.
The rapid development of non-existing infrastructure makes the ad hoc network
easily to be used in emergency situation.
 Bluetooth: Bluetooth can provide short range communication between the
nodes such as a laptop and mobile phone.

8. 8
The advantages of an ad hoc network
include:
 Separation from central network administration.
 Self-configuring nodes are also routers.
 Self-healing through continuous re-configuration.
 Scalability incorporates the addition of more nodes.
 Mobility allows ad hoc networks created on the fly in any situation
where there are multiple wireless devices.
Flexible ad hoc can be temporarily setup at anytime, in any place.
 Lower getting-started costs due to decentralized administration.
 The nodes in ad hoc network need not rely on any hardware and
software. So, it can be connected and communicated quickly.

9. Types of Ad Hoc Networks
 MANET
 WSN
 WMN
 VANETs

10. A MANET
Mobile Adhoc Network
10
http://www.comp.nus.edu.sg/~xuemingq/research.html

11. Mobile Devices
11
 Laptop computers
 Pagers, cellular phones, PDAs
 In-car navigators -Dash Express
 Dash units talk to each other and form
a network that connects to the Internet
 Traffic speed data is sent back to the company,
then broadcast back to all local dash units
 Sensors
 ……

12. Wireless Sensor Network (WSN)
12
 An emerging application area for MANETs
 A collection of cheap to manufacture, stationary,
tiny sensors
 Network lifetime -- power as a major driving
issue
 Battlefield surveillance, environment monitoring,
health care, etc.

13. WSN Example
13
http://www.alicosystems.com/wireless%20sensor.htm

14. Other MANETs applications
14
 Collaborative work
 Crisis-management applications
 Personal Area Networking (PAN)

15. MANET
 A Mobile Ad-hoc Network (MANET) is a collection of autonomous nodes or
terminals which communicate with each other by forming a multi-hop radio
network and maintaining connectivity in a decentralized manner over relatively
bandwidth constrained wireless links..
 Each device in a MANET is free to move independently in any direction, and
will therefore change its links to other devices frequently.
 The topology is highly dynamic and frequent changes in the topology may be
hard to predict.

16. Multi hop communication
 May need to traverse multiple links to reach
destination
 Mobility causes route changes

17. Network Architecture
17

18. Difference between Cellular and Ad-hoc
Networks
Cellular Networks Ad-hoc Networks
Fixed, pre-located cell sites and base
stations.
Slow Deployment
No fixed base stations,
Very rapid deployment.
Static backbone network topology
Single Hop
Highly dynamic network topologies,
Single and Multihop Communication
Relatively favorable environment
Stable connectivity.
Hostile environment (losses, noise)
Irregular connectivity.
Detailed planning before base stations
can be installed.
Ad-hoc network automatically forms
and conforms to change.

19. Cellular Wireless
 Single hop wireless connectivity to the wired world
 Space divided into cells
 A base station is responsible to communicate with hosts in its cell
 Mobile hosts can change cells while communicating
 Hand-off occurs when a mobile host starts communicating via a new
base station

20. Security Requirements in MANETs
20
 Availability
 Authorization and Key Management
 Data Confidentiality
 Data Integrity
 Non-repudiation

21. Challenges/Issues in Adhoc
21
 No infrastructure
 Peer-to-peer architecture with multi-hop routing
 Mobile device physical vulnerability
 Stringent resource constraints
 Wireless medium
 Node mobility

22. Threats
22
 Attacks
 External attacks
 Internal attacks
 Passive attacks
 Active attacks
 Misbehavior

23. MANET Routing Protocols
23
 Topology-based approaches
 Proactive routing (table driven)
 Reactive routing (on demand)
 Hybrid routing
 Position-based approaches

24. Comparison
24
 Proactive routing
 Proactive routing protocols are also called as table
driven routing protocols.
 In this every node maintain routing table which
contains information routes to all possible destinations.
 The routing tables are updated periodically whenever
the network topology changes
 Not suitable for large networks as they need to maintain
node entries for each and every node in the routing table
of every node
 E.g. DSDV, WRP, TBRPF, OLSR, etc.

25. 25
 Reactive routing
 Reactive routing protocol is also known as on demand routing
protocol
 Route is discovered whenever it is needed
 Two major components

1) Route discovery: In this phase source node initiates route
discovery on demand basis. Source nodes consults its route cache
for the available route from source to destination otherwise if the
route is not present it initiates route discovery. The source
node, in the packet, includes the destination address of the node
as well address of the intermediate nodes to the destination.
2) Route maintenance: Due to dynamic topology of the network
cases of the route failure between the nodes arises due to link
breakage etc, so route maintenance is done. Reactive protocols
have acknowledgement mechanism due to which route
maintenance is possible
 E.g. DSR, ADOV, TORA, etc.

26. 26
Hybrid routing protocol
Ccombination of both proactive and reactive routing
protocol.
Proactive protocols have large overhead and less latency
while reactive protocols have less overhead and more
latency
It uses the route discovery mechanism of reactive
protocol and the table maintenance mechanism of
proactive protocol so as to avoid latency and overhead
problems in the network

27. DSR vs. AODV
27
 Dynamic source routing (DSR)
 Source broadcasts RREQ through the network
 Intermediate nodes add its address to RREQ and continue
broadcasting until RREP received
 Full path chosen by source and put into each packet sent
 Ad hoc on-demand distance vector (AODV)
 Hop-by-hop routing
 Source sends RREQ to neighbors
 Each neighbor does so until reach the destination
 Destination node sends RREP follow the reverse path
 Source doesn’t put whole path but only next hop addrress in
outgoing packets

28. Route Discovery in DSR
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
Represents a node that has received RREQ for D from S

29. Route Discovery in DSR
B
A
S E
F
H
J
D
C
G
I
K
Represents transmission of RREQ
Z
Y
Broadcast transmission
M
N
L
[S]
[X,Y] Represents list of identifiers appended to RREQ

30. Route Discovery in DSR
B
A
S E
F
H
J
D
C
G
I
K
Z
• Node H receives packet RREQ from two neighbors:
potential for collision
Y
M
N
L
[S,E]
[S,C]

31. Route Discovery in DSR
B
A
S E
F
H
[S,E,F]
J
D
C
G
I
K
Z
Y
M
N
L
[S,C,G]
• Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once

32. Route Discovery in DSR
B
A
S E
F
H
[S,E,F,J]
J
D
C
G
I
K
Z
Y
M
• Nodes J and K both broadcast RREQ to node D
• Since nodes J and K are hidden from each other, their
transmissions may collide
N
L
[S,C,G,K]

33. Route Discovery in DSR
B
A
S E
F
H
J
[S,E,F,J,M]
D
C
G
I
K
Z
Y
M
• Node D does not forward RREQ, because node D
is the intended target of the route discovery
N
L

34. Route Discovery in DSR
 Destination D on receiving the first RREQ, sends a Route Reply (RREP)
 RREP is sent on a route obtained by reversing the route appended to
received RREQ
 RREP includes the route from S to D on which RREQ was received by
node D

35. Route Reply in DSR
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
RREP [S,E,F,J,D]
Represents RREP control message

36. Dynamic Source Routing (DSR)
 Node S on receiving RREP, caches the route
included in the RREP
 When node S sends a data packet to D, the
entire route is included in the packet header
 hence the name source routing
 Intermediate nodes use the source route included
in a packet to determine to whom a packet should
be forwarded

37. Data Delivery in DSR
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
DATA [S,E,F,J,D]
Packet header size grows with route length

38. AODV
 Route Requests (RREQ) are forwarded in a manner similar to DSR
 When a node re-broadcasts a Route Request, it sets up a reverse path
pointing towards the source
 AODV assumes symmetric (bi-directional) links
 When the intended destination receives a Route Request, it replies by
sending a Route Reply (RREP)
 Route Reply travels along the reverse path set-up when Route Request
is forwarded

39. AODV Forward path setup
 RREQ arrives at a node that has current route to the destination (
larger/same sequence number)
 unicast request reply (RREP)<source_addr, dest_addr,
dest_sequence_#, hop_cnt,lifetime> to neighbor
 RREP travels back to the source along reverse path
 each upstream node updates dest_sequence_#, sets up a forward
pointer to the neighbor who transmit the RREP

40. AODV Reverse path setup
 Counters : Sequence number, Broadcast id
 Reverse Path
 Broadcast route request (RREQ) < source_addr, source_sequence-# ,
broadcast_id, dest_addr, dest_sequence_#, hop_cnt >
 RREQ uniquely identified by <source_addr , broadcast_id>
 Route reply (RREP) if neighbor is the target, or knows a higher
dest_sequence_#
 Otherwise setup a pointer to the neighbor from whom RREQ was
received
 Maintain reverse path entries based on timeouts

41. Route Requests in AODV
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
Represents a node that has received RREQ for D from S

42. Route Requests in AODV
B
A
S E
F
H
J
D
C
G
I
K
Represents transmission of RREQ
Z
Y
Broadcast transmission
M
N
L

43. Route Requests in AODV
B
A
S E
F
H
J
D
C
G
I
K
Represents links on Reverse Path
Z
Y
M
N
L

44. Reverse Path Setup in AODV
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
• Node C receives RREQ from G and H, but does not forward
it again, because node C has already forwarded RREQ once

45. Reverse Path Setup in AODV
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L

46. Reverse Path Setup in AODV
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
• Node D does not forward RREQ, because node D
is the intended target of the RREQ
N
L

47. Forward Path Setup in AODV
B
A
S E
F
H
J
D
C
G
I
K
Z
Y
M
N
L
Forward links are setup when RREP travels along
the reverse path
Represents a link on the forward path

48. Route Request and Route Reply
 Route Request (RREQ) includes the last known sequence number for
the destination
 An intermediate node may also send a Route Reply (RREP) provided
that it knows a more recent path than the one previously known to
sender
 Intermediate nodes that forward the RREP, also record the next hop to
destination
 A routing table entry maintaining a reverse path is purged after a
timeout interval
 A routing table entry maintaining a forward path is purged if not used
for a active_route_timeout interval