An ad hoc network is a type of wireless network that does not require a central router or base station. Nodes communicate directly with each other or through intermediate nodes in a multi-hop fashion without any fixed infrastructure. Routing and resource management are distributed. Common types include wireless mesh networks, wireless sensor networks, and hybrid wireless networks. Ad hoc networks face challenges related to medium access, routing, security, and resource constraints due to the lack of centralized control.

1. DARPAN DEKIVADIYA
(09BCE008)

2. Introduction
 In computer networking, an ad hoc network refers to a
network connection established for a single session
and does not require a router or a wireless base station.
 It is defined as the category of wireless network that
utilize multi-hop radio relaying and capable of
operating without the support of any fixed
infrastructure . hence, is also called infrastructure -less
network.
 Routing and Resource management are done in a
distributed manner.

3. Types of wireless networks
Wireless
mesh
Cellular network
Hybrid
wireless wireless
network network
Wireless
sensor
network
Single hop wireless network Multi hop wireless network
or
Ad hoc network

4. Types of Ad hoc network
1. Wireless mesh network
 formed to provide an alternate communication infrastructure
for mobile or fixed nodes/users, without the spectrum reuse
constraints and the requirements of network planning of
cellular networks.
2. Wireless sensor network
 used to provide a wireless communication infrastructure
among the sensors deployed in a specific application domain.

5. 3. Hybrid wireless network
 when two nodes in the same cell want to
communicate with each other, the connection is
routed through multiple wireless hops over the
intermediate nodes. the base station maintains the
information about the topology of the network for
efficient routing.

6. Cellular network
Base station
A B
E C
D
Mobile node

7. Ad hoc wireless network
Wireless link
A B
E C
D
Mobile node

8. Difference
Cellular network Ad hoc network
 Fixed infrastructure  No infrastructure
 Single hop wireless  Multi hop wireless
link link
 Centralized routing  Distributed routing
 High cost  Low cost
 Seamless connectivity  Frequent path breaks
due to mobility

9. Characteristics
 Operating without a central coordinator
 Multi-hop radio relaying
 Frequent link breakage due to mobile nodes
 Constraint resources (bandwidth, computing
power, battery lifetime).
 Instant deployment

10. Applications
 Military applications
 Collaborative computing
 Emergency rescue
 Mesh networks
 Wireless sensor networks
 Multi-hop cellular networks
 Wireless Community Network

11. General Issue for Ad hoc network
 Medium access scheme
 Distributed operation
 Synchronization
 Hidden terminal
 Access delay
 Fairness
 Resource reservation
 Capability of power control

12. General Issue for Ad hoc network
 Routing
 Mobility
 Bandwidth constraint
 Error prone
 Minimum rout acquisition
 Quick rout reconfiguration
 Loop free routing
 Security and privacy

13. General Issue for Ad hoc network
 Multicasting
 Robustness
 Efficiency
 Quality of services
 Efficient group management
 Scalability
 Security

14. General Issue for Ad hoc network
 Transport layer protocol
 UDP
 TCP
 TORA
 SMR
 Pricing Scheme
 Self organization

15. General Issue for Ad hoc network
 Security
 Denial of services
 Resource consumption
 Energy depletion
 Buffer overflow
 Interference
 Addressing and Service Discovery

16. SECURITY REQUIREMENT
Availability
Confidentiality
Integrity
authentication

17. Infrastructure based versus Ad Hoc Networks
 Infrastructure Networks contain special nodes called access
points(APs), which are connected via existing networks.
APs are special in the sense that they can interact with
wireless nodes as well as with the existing wired network.
The other wireless nodes , also known as mobile stations ,
communicate via APs. The APs also act as bridges with
other networks.
 Ad hoc LANs do not need any fixed infrastructure. These
networks can be set up on the fly at any place. Nodes
communicate directly with each other or forward messages
through other nodes that are directly accessible.

18.  The design of infrastructure based networks is simpler
because most of the network functionality lies within
the access point ,whereas the client can remain quite
simple.
 In Ad hoc networks, the complexity of each node is
higher because every node has to implement medium
access mechanisms to provide certain quality of
service.
 Infrastructure based networks lose some of the
flexibility which wireless networks can offer.
e.g. They cannot be used for disaster relief in cases
where no infrastructure is left, where ad hoc networks
can be used.

19. Architecture of Ad Hoc Network
 IEEE 802.11 Specifies the most famous family
WLAN in which many products are available
 802.11 is a set of IEEE standards that govern
wireless networking transmission methods.
 Under 802.11 standards mobile terminals can
operate in two modes
1. Infrastructure Mode
2. Ad Hoc Mode

20. Ad Hoc Mode
 IEEE 802.11 only covers PHY layer and MAC layer
 PHY layer is subdivided into
1. Physical Layer Convergence Protocol (PLCP)
2. Physical Medium Dependent sub layer (PMD)
 PHY management include channel tuning and
responsible for higher layer functions
(e.g. control of bridging)
 MAC management controls authentication
mechanism and power management to save battery
power.

21. MAC Layer
 Provides “ Asynchronous Data Service “ and “ Time
Bounded Service “
 802.11 only offers the “ Asynchronous Data Service “ in
Ad-hoc Mode , but both services can be offered by
Infrastructure Mode.
 Basic access mechanism defined for IEEE 802.11 are
1. Distributed Coordination Function (DCF)
2. Point Coordination Function (PCF)
 DCF only offers asynchronous service , while PCF
offers both asynchronous and time bounded service
 MAC mechanism also called distributed foundation
wireless medium access control (DFWMAC)

22. Basic DFWMAC using CSMA/CA
 Mandatory access mechanism for IEE 802.11 is based
on CSMA/CA
 CSMA/CA mechanism shown in figure.


23.  If medium is busy , nodes have to wait for the duration of
DIFS , entering a contention phase.
 Each node now choose a random back off time within a
contention window and delays medium access for this
random amount of time.
 As soon as a node senses the channel is busy , it has lost this
cycle and has to wait for the next chance.
 The basic CSMA/CA mechanism is not fair
 To provide fairness , IEEE 802.11 adds back off timer
 Each node selects random amount of waiting time
 If certain station does not get access to the medium in first
cycle it stops its back off timer , waits for the channel to be
idle again for DIFS and starts the counter again.

24. DFWMAC with RTS/CTS
 Hidden terminal problem may occur in 802.11 ,if one
station can receive two others, but those cannot
receive each other.
 To deal with this problem, mechanism using two
control packets , RTS and CTS .
 After waiting for DIFS , the sender can issue a request
to send (RTS) control packet.
 Every node receiving this RTS now has to set its net
allocation vector (NAV) in accordance with the
duration field
 The NAV than specifies earliest point at which the
station can try to access the medium.

25.  If the receiver receives the RTS , it answers with the
clear to send (CTS) waiting for SIFS
 This CTS packet contains duration field and receivers
have to adjust their NAV.
 Now all nodes within receiving distance around sender
and receiver are informed that they have to wait more
time before accessing the medium.
 This mechanism reserves the medium for one sender
exclusively.
 It is also called a Virtual Reservation Scheme.

26. ROUTING ALGORITHM
 TABLE DRIVEN
 Maintain the route table
 The Wireless Routing Protocol localizes the updates to
immediate neighbors.
 The Cluster Gateway Switch Routing
protocol reduces the size of the tables and amount of
information propagation by having each cluster of
nodes select a cluster head.

27. Source initiated on demand
 On-demand routing protocols are characterized by a
path discovery mechanism which is initiated when a
source needs to communicate with a destination that it
does not know how to reach.

28. Classification of protocols
 Based on the routing information update
mechanism
 Proactive or table-driven routing protocols
 Reactive or on demand routing protocols
 Hybrid routing protocols
 Based on the use of Temporal information for
Routing
 Routing protocols using past temporal information
 Routing protocols that use future temporal information

29.  Based on Topology Information Organization
 Flat topology routing protocols
 Hierarchical topology routing protocols
 Based on the Utilization of specific Resources
 Power aware routing
 Geographical information assisted routing

30. Table Driven Routing Protocol
 Destination sequenced distance-vector protocol
(DSDV)
According to this protocol every node maintains
a table that contains the shortest distance and
the first node on the shortest path to every
other node in the network.
It incorporate table update with increasing
sequence number tag to prevent loops, to
counter to the count-to-infinity problem, and
for faster convergences.

31. DSDV (continue ..)
Destination Next Hop Distance Sequence Number
A’s routing table :
A A 0 S205_A
B B 1 S334_B
C C 1 S198_C
D D 1 S567_D
E D 2 S767_E
F D 2 S45_F

32. Advantage of DSDV
 The availability of the routers to all destination at all
times implies that much less delay is involved in the
route setup process.
 The mechanism of incremental updates with sequence
number tags makes the existing wired network
protocol adaptable to ad hoc networks.
 Hence wired network protocol can be applied to the ad
hoc network by less modification.

33. Disadvantage of DSDV
 A small network with high mobility or a large network
with low mobility can completely choke the available
bandwidth. Hence this protocol suffers from excessive
control overhead that is proportional to the number of
nodes in the network.
 In order to obtain information about a particular
destination node, a node has to wait for a table update
message initiated by the same destination node.

34. Wireless Routing protocol
 It is also known as WRP protocols.
 It is same as DSDV protocol ,but contain some
additional flag in table like status of the path which is
simple path(correct) or a loop(error), or the
destination node not marked(null).

35. Advantage of WRP
 It is the faster convergence and involves fewer table
updates.

36. Disadvantage of WRP
 Complexity of maintenance of multiple tables
demands a larger memory and greater processing
power from the nodes.
 At the high mobility, the control overhead involved in
updating table entries is almost the same as DSDV. So
it is not suitable for highly dynamic and also for very
large ad hoc networks.

37. Cluster head Gateway Switch Routing
protocol
 It is also called CGSR protocols
 CGSR organizes nodes into clusters, with coordination
among the member of each cluster instructed nodes
named “cluster head”.
 CGSR protocol creates a fixed region in the network.
Each node in the cluster region is known as cluster
member and they all are connected with pivot node
which is called cluster-head .Two cluster region are
connected via node which are place in intersection
region of two cluster region and called cluster-gateway.

39. Advantage
 CGSR is a hierarchical routing scheme which enables
partial coordination between nodes by electing
cluster-heads. Hence , better bandwidth utilization is
possible.
 It is easy to implement priority scheduling scheme
with token scheduling and gateway code scheduling.

40. Disadvantage
 It increases in path length and instability in the system
at high mobility when the rate of change of cluster-
heads is high.
 To avoid gateway conflicts, more resources are
required.
 The power consumption at the cluster-head node is
also a matter of concern because the battery-draining
rate at the cluster-head is higher than that at a normal
node.

41. On-Demand routing protocols
 Dynamic Source Routing Protocol (DSR)
 In this routing protocol does not require periodic
‘hello’ packet transmission, which are used by a node
to inform its neighbors of its presence. The basic
approach of this protocol during the routing
construction phase is to establish a route by flooding
Route-Request packets in the network. The
destination node,
 On receiving a Route-Request packet, respond by
sending Route-Reply packets back to the resource.

43. Advantage
 Do not exchange routing update periodically, so
overhead transmission is greatly reduced
 Can refer to cache for the new route when link fails.

44. Disadvantages
 Scalability problem: High route discovery latency for
large network.
 High mobility problem: although the packet dropped
may not be substantional, the overhead traffic will
increase a lot.

45. Ad Hoc On-Demand Distance
Vector
 In AODV, a field of the number of hops is used in the
route record, instead of a list of intermediate router
addresses.
 Each intermediate router sets up a temporary reverse
link in the process of a route discovery.
 This link points to the router that forwarded the
request.

46. Advantage
 AODV is loop-free due to the destination sequence
numbers associated with routes. Therefore, it offers
quick convergence when the ad hoc network topology
changes which, typically, occurs when a node moves in
the network
Disadvantage
 Poor scalability is a disadvantage of AODV.

47. Hybrid routing protocols
 Zone Routing Protocol (ZRP)
 ZRP is formed by two
 sub-protocols, the Intrazone Routing Protocol (IARP)
and the Interzone Routing Protocol (IERP).

48.  IARP is “a limited scope proactive routing protocol
used to improve the performance of existing globally
reactive routing protocols”. It relies on the service of a
certain neighbor discovery protocol (NDP) to provide
neighbor information. IARP may use a scheme based
on the time-to-live (TTL) field in IP packets to
control the zone range.
 IERP is the reactive routing component of ZRP. This
scheme is responsible for finding a global path. It
avoids global queries for destinations that would be
sent to surrounding hop neighbors. When global
queries are required, “the routing zone based
broadcast service can be used to efficiently guide
route queries outward, rather than blindly relaying
queries from neighbor to neighbor” .

49. References
 Mobile Communications
- Jochen H. Schiller
 Ad Hoc Wireless Networks
- C. Siva Ram Murthy
- B. S. Manoj

50. THANKYOU
?