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
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
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
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
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