1. ADHOC AND SENSORS NETWORKS –
INTRODUCTION AND ROUTING
PROTOCOLS:
PRESENTED BY:
Harjot Singh
AP
CSE,CEC
6. Wireless network
Computer networks that are not connected by
cables are called wireless networks. They
generally use radio waves for communication
between the network nodes. They allow devices
to be connected to the network while roaming
around within the network coverage.
8. Types of Wireless Networks
Wireless LANs Connects two or more network
−
devices using wireless distribution techniques.
Wireless MANs Connects two or more wireless
−
LANs spreading over a metropolitan area.
Wireless WANs Connects large areas
−
comprising LANs, MANs and personal networks
9. Advantages of Wireless Networks
It provides clutter-free desks due to the absence of wires and cables.
It increases the mobility of network devices connected to the system
since the devices need not be connected to each other.
Accessing network devices from any location within the network
coverage or Wi-Fi hotspot becomes convenient since laying out
cables is not needed.
Installation and setup of wireless networks are easier.
New devices can be easily connected to the existing setup since they
needn’t be wired to the present equipment. Also, the number of
equipment that can be added or removed to the system can vary
considerably since they are not limited by the cable capacity. This
makes wireless networks very scalable.
Wireless networks require very limited or no wires. Thus, it reduces
the equipment and setup costs.
10. Examples of wireless networks
Mobile phone networks
Wireless sensor networks
Satellite communication networks
Terrestrial microwave networks
11. A BSS without an AP is called an ad hoc network;
a BSS with an AP is called an infrastructure network
12. What Is an Ad Hoc Network?
• An ad hoc wireless network is a collection of two or more
devices equipped with wireless communications and
networking capability.
• Such devices can communicate with another node that is
immediately within their radio range or one that is
outside their radio range.
• For the latter scenario, an intermediate node is used to
relay or forward the packet from the source toward the
destination.
• Since an ad hoc wireless network does not rely on any fixed
network entities, the network itself is essentially
infrastructure-less. There is no need for any fixed radio
base stations, no wires or fixed routers.
13. • An ad hoc wireless network is self-organizing and adaptive.
• This means that a formed network can be de-formed on-the-
fly without the need for any system administration.
• The term "ad hoc" tends to imply "can take different forms"
and "can be mobile, standalone, or networked.“
• Ad hoc nodes or devices should be able to detect the
presence of other such devices and to perform the necessary
handshaking to allow communications and the sharing of
information and services.
14. Wireless Ad-hoc Network
• A wireless adhoc network is a decentralized type of wireless
network.
• The network is adhoc because it does not rely on a pre-
existing infrastructure, such as routers in wired networks or
access points in managed (infrastructure) wireless networks.
• Each node participates in routing by forwarding data for other
nodes, and so the determination of which nodes forward data
is made dynamically based on the network connectivity.
• In addition to the classic routing, adhoc networks can use
flooding for forwarding the data
15. Mobile Ad Hoc Networks (MANET)
• Selfconfiguring network of mobile routers (and
associated hosts) connected by wireless links
• This union forms a random topology
• Routers move randomly free
• Topology changes rapidly and unpredictably
• Standalone fashion or connected to the larger Internet
• While MANETs are selfcontained, they can also be tied to an
IP-based global or local network–Hybrid MANETs
• Suitable for emergency situations like natural or human-
induced disasters, military conflicts, emergency medical
situations, etc.
16. Issues in Ad-Hoc
• Ad hoc wireless devices can take different forms (for example,
palmtop, laptop, Internet mobile phone, etc.),the
computation, storage, and communications capabilities and
interoperability of such devices will vary tremendously.
• Ad hoc devices should not only detect the presence of
connectivity with neighbouring devices/nodes, but also
identify what type the devices are and their corresponding
attributes.
• Due to the presence of mobility, routing information will have
to change to reflect changes in link connectivity.
• The diversity of ad hoc mobile devices also implies that the
battery capacity of such devices will also vary. Since ad hoc
networks rely on forwarding data packets sent by other
nodes, power consumption becomes a critical issue.
17. Issues in Ad hoc wireless networks
• Medium access scheme
• Routing, Multicasting, TPC protocol
• Pricing scheme, QoS, Self-organization
• Security, Energy management
• Addressing and service discovery
• Deployment considerations
18. Issues in Ad hoc wireless networks
The major issues that affect the design,
deployment, & performance of an ad hoc
wireless network system are Medium Access
Control (MAC). The primary responsibility of a
Medium Access Control (MAC) protocol in ad hoc
wireless networks is the distributed arbitration
for the shared channel for transmission of
packets.
19. The major issues to be considered in designing a
MAC protocol for ad hoc wireless networks are
as follows :
1. Distributed Operation 2. Synchronization 3.
Hidden Terminals 4. Exposed terminals 5.
Throughput 6. Access delay 7. Fairness 8. Real-
time Traffic support 9. Resource reservation 10.
Ability to measure resource availability 11.
Capability for power control 12. Adaptive rate
control 13. Use of directional antennas
20. Issues in Ad hoc wireless networks
Distributed operation
Ad hoc wireless network do not have central
coordinator to distribute bandwidth fairly among
nodes. Therefore nodes must be scheduled in a
distributed fashion for gaining access to the
channel and for this exchange of control
information among nodes is required. Therefore
the MAC protocol design should be fully
distributed and must make sure that the additional
overhead incurred due to this control information
exchange is not Elevated
21. Issues in Ad hoc wireless networks
Synchronization is very important for bandwidth
reservations by nodes.
The MAC protocol must take into consideration the
synchronization between nodes in the network.
The MAC protocol design should take into account the
requirement of time synchronization. Synchronization is
mandatory for TDMA- based systems for management of
transmission and reception slots. Synchronization
involves usage of scarce resources such as bandwidth
and battery power.
The control packets used for synchronization can also
increase collisions in the network.
22. Issues in Ad hoc wireless networks
Hidden terminals are nodes that are hidden(or not reachable)
from the sender of a data transmission session, but are
reachable to the receiver of the session. In such cases, the
hidden terminal can cause collisions at the receiver node. The
presence of hidden terminals can significantly reduce the
throughput of a MAC protocol used in ad hoc wireless networks.
Exposed terminals
Exposed terminals, the nodes that are in the transmission range
of the sender of an on –going session, are prevented from
making a transmission. In order to improve the efficiency of the
MAC protocol, the exposed nodes should be allowed to transmit
in a controlled fashion without causing collision to the on-going
data transfer.
23. Issues in Ad hoc wireless networks
Throughput
The MAC protocol employed in ad hoc wireless networks should attempt
to maximize the throughput of the system. The important considerations
for throughput enhancement are Minimizing the occurrence of
collisions. Maximizing channel utilization and Minimizing control
overhead
Access delay
The average delay that any packet experiences to get transmitted. The MAC
protocol should attempt to minimize the delay.
Fairness
Fairness refers to the ability of the MAC protocols to provide an equivalent
share or weighted share of the bandwidth to all competing nodes.
Fairness can be either node-based or flow based. The former attempts
to provide an equal bandwidth to all competing nodes where the later
provides an equal share for competing data transfer session
24. Issues in Ad hoc wireless networks
Real-time Traffic support
In a contention-based channel access
environment, without any central coordination,
with limited bandwidth, and with location-
dependent contention, supporting time- sensitive
traffic such as voice, video, and real-time data
requires explicit support from the MAC protocol
25. Challenges in Ad Hoc Networks
• Limited wireless transmission range
• Broadcast nature of the wireless medium
• Packet losses due to transmission errors
• Mobility-induced route changes
• Mobility-induced packet losses
• Battery constraints
• Potentially frequent network partitions
• Ease of snooping on wireless transmissions (security hazard)
26. Issues in Ad Hoc Networks
1.Spectrum Allocation and Purchase
2.Medium access scheme
3.Routing
4.Multicasting
5.Transport layer protocol Performance
6.Pricing scheme
7.QoS provisioning
8.Security
9.Energy management
10.Addressing and service discovery
11.Scalability
12.Deployment considerations
27. Spectrum Allocation and Purchase
• FCC control the regulations regarding the use of
radio spectrum.
• Who regulates the use of radio spectrum in INDIA??
• Toprevent interference, ad hoc networks operate
over some form of allowed or specified spectrum range.
• Most microwave ovens operate in the 2.4GHz band, which
can therefore interfere with wireless LAN systems.
• Frequency spectrum is not only tightly controlled
and allocated, but it also needs to be purchased.
• With ad hoc networks capable of forming and deforming
on-the-fly, it is not clear who should pay for this spectrum.
28. Medium Access Scheme
• Distributed operation
• Synchronization
• Hidden terminal problem
• Exposed terminal problem
• Throughput
• Access delay
• Fairness: especially for relaying nodes
• Real-time traffic support
• Resource reservation
• Ability to measure resource availability
• Capability for power control
• Adaptive rate control
• Use of directional antennas
29. Routing
• Challenges
• Mobility
• results in path breaks, packet collisions, transient loops, stale
routing information, and difficulty in resource reservation
• BW constraints
• Error-prone and shred channel
• Bit error rate BER:10-5~ 10-3wireless vs. 10-12~ 10-9 wired
• Location-dependent contention
• Distribute load uniformly
30. • The presence of mobility implies that links make and break often
and in an indeterministic fashion.
• Classical distributed Bellman-Ford routing algorithm is used to
maintain and update routing information in a packet radio
network.
• Yet distance-vector-based routing not designed for wireless
networks, still applicable to packet radio networks since the rate
of mobility is not high.
• Mobile devices are now small, portable, and highly integrated.
• Ad hoc mobile networks are different from packet radio networks
since nodes can move more freely, resulting in a dynamically
changing topology.
• Existing distance-vector and link-state-based routing protocols are
unable to catch up with such frequent link changes in ad hoc
wireless networks, resulting in poor route convergence and very
low communication throughput. Hence, new routing protocols are
needed
31. Multicasting
• Multiparty communications are enabled through the presence
of multicast routing protocols.
• The
multicast
(MBone) comprises an
interconnection of
backbone
multicast routers that are capable
of
tunnelling multicast packets through non-multicast routers.
• Some multicast protocols use a broadcast-and-prune
approach to build a multicast tree rooted at the source .
Others use core nodes where the multicast tree originates.
• All such methods rely on the fact that routers are static, and
once the multicast tree is formed, tree nodes will not move.
However, this is not the case in ad hoc wireless networks.
32. 5. Energy Efficiency
devices
today
• Mobile
Batter
y
are mostlyoperated by
batteries. technologyis still lagging
behind microprocessor
technology.
• The lifetime of an Li-ion battery today is only 2-3 hours. Such a
limitation in the operating hours of a device implies the need
for power conservation.
• For ad hoc mobile networks, mobile devices must perform
both the role of an end system (where the user interacts and
where user applications are executed) and that of an
intermediate system (packet forwarding).
• Hence, forwarding packets on the behalf of others will
consume power, and this can be quite significant for nodes in
an ad hoc wireless network.
33. 6. TCP Performance
• TCP is an end-to-end protocol designed to provide flow and
congestion control in a network. TCP is a connection-oriented
protocol ; hence, there is a connection establishment phase
prior to data transmission. The connection is removed when
data transmission is completed.
• TCP(Transmission Control Protocol) assumes that nodes in the
route are static, and only performs flow and congestion
activities at the SRC and DEST nodes.
34. 7. Service Location, Provision, and
Access
• Adhoc networks
comprise
heterogeneous devices and
machines and not every one is capable of being a server.
• The concept of a client initiating task requests to a server
for execution and awaiting results to be returned may not
be attractive due to limitations in bandwidth and power.
• Concept of remote programming as used in mobile agents
is more applicable since this can reduce the interactions
exchanged between the client and server over the wireless
media.
• Also, how can a mobile device access a remote service in an
ad hoc network? How can a device that is well-equipped
advertise its desire to provide services to the rest of the
members in the network? All these issues demand
research.
35. 8. Security & Privacy
• Ad hoc networks are intranets and remain as intranets unless
connected to Internet.
• Such confined communications have already isolated attackers
who are not local in the area.
• Through neighbor identity authenication, a user can know if
neighboring users are friendly or hostile.
• Information sent in an ad hoc route can be protected in some
way but since multiple nodes are involved, the relaying of
packets has to be authenicated by recognizing the originator
of the packet and the flow ID or label
36. 9. Deployment Consideration
• Adv. in ad hoc net
• Low cont of deployment
• Incremental deployment
• Short deployment time
• Reconfigurablity
• Scenario of deployment
• Military deployment: data-centric or user-centric
• Emergency operation deployment: hand-held, voice/data, <
100 nodes
• Commercial wide-area deployment: e.g. WMN
• Home network deployment
37. List of ad hoc routing protocols
Table-driven (proactive) routing
This type of protocols maintains fresh lists of
destinations and their routes by periodically
distributing routing tables throughout the
network. The main disadvantages of such
algorithms are:
Respective amount of data for maintenance.
Slow reaction on restructuring and failures.
38. List of ad hoc routing protocols
On-demand (reactive) routing
This type of protocol finds a route on demand by
flooding the network with Route Request
packets. The main disadvantages of such
algorithms are:
High latency time in route finding.
Excessive flooding can lead to network clogging.
