2. Introduction
Introduction - Ad Hoc Network definition
Characteristic/features and application
Heterogeneity in Mobile Devices
Wireless Sensor Networks
Traffic Profiles
Types ofAd Hoc Mobile Communications
Types of Mobile Host Movements
Challenges FacingAd Hoc Mobile Networks
Issues and Challenges Facing Ad Hoc Mobile network
Ad Hoc wireless Internet
2
3. A BSS without an AP is called an ad hoc network;
a BSS with an AP is called an infrastructure network.
3
4. Ad hoc networks
Temporary network composed of mobile nodes without preexisting
communication infrastructure, such as Access Point (AP) and Base Station
(BS).
Each node plays the role of router for multi-hop routing.
Self-organizing network without infrastructure networks
Started from DARPA PRNet in 1970
Cooperative nodes (wireless)
Each node decode-and-forward packets for other nodes
Multi-hop packet forwarding through wireless links
Proactive/reactive/hybrid routing protocols
Most works based on CSMA/CA to solve the interference problem
IEEE 802.11 MAC
4
5. What Is an Ad Hoc Network?
An ad hoc wireless network
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.
5
6. (cont…)
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.
6
7. Wireless Ad-hoc Network
A wireless ad-hoc network is a decentralized type
of wireless network.
The network is ad hoc 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, ad hoc networks can
use flooding for forwarding the data.
7
8. Mobile Ad Hoc Networks (MANET)
Mobile nodes
Access points
Backbone
Wireless Mobile Network
MANET
8
9. Mobile Ad-hoc Network
Self-configuring 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 self contained, 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.
9
12. MANET Application
Applications Descriptions/Services
Tactical Networks •Military communication, operations
•Coordination of military object moving at high speeds such as fleets
of airplanes or ships
•Automated battlefields
Sensor networks •Collection of embedded sensor devices used to collect real time data
to automate everyday functions. Data highly correlated in time and
space, e.g., remote sensors for weather, earth activities; sensors for
manufacturing equipments.
•Can have between 1000 -100,000 nodes, each node collecting sample
data, then forwarding data to centralized host for processing using low
homogeneous rates.
Emergency
services
•Search, rescue, crowd control, and commando operations as well as
disaster recovery
•for e.g. Early retrieval and transmission of patient data ( record,
status, diagnosis ) from /to the hospital
•Replacement of a fixed infrastructure in case of earthquakes,
hurricanes, fire etc.12
13. MANET Application
Applications Descriptions/Services
Commercial
environments
•E-commerce, e.g., electronic payments from anywhere (i.e., in taxi).
•Business:
dynamic access to customer files stored in a central location
on the fly provide consistent databases for all agents
Mobile office
•Vehicular services:
transmission of news ,road conditions ,weather, music
local ad hoc network with nearby vehicles for road/accident
guidance
Home and
enterprise
networking
•Home/office wireless networking(WLAN), e.g., shared whiteboard
application, use PDA to print anywhere, trade shows
•Personal area network (PAN)
Educational
applications
•Set up virtual classrooms or conference rooms
•Set up ad hoc communication during conferences, meetings, or
lectures13
14. MANET Application
Applications Descriptions/Services
Entertainment Multiuser games
Robotic pets
outdoor internet access
Location- aware
Services
Follow- on services, e.g., automatic call forwarding, transmission of the
actual workspace to the current location
Information services
push, e.g., advertise location-specific services, like gas stations
pull, e.g., location-dependent travel guide; services( printer, fax,
phone, server, gas stations) availability information; caches,
intermediate results, state information, etc.
14
15. 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.15
16. Heterogeneity in Mobile Devices
(a) Heterogeneous mobile device ad hoc networks, and (b) homogeneous ad hoc
network comprising powerful laptop computers.16
17. Heterogeneity in Mobile Devices
The presence of heterogeneity implies that some devices are
more powerful than others, and some can be servers while
others can only be clients.
It is evident that there are differences in size, computational
power, memory, disk, and battery capacity.
Mobile devices can exist in many forms.There are great
differences among these devices,
heterogeneity can affect communication performance and
the design of communication protocols.
17
21. INTRODUCTION TO WSN
A wireless sensor network is one form of an ad hoc wireless
network.
A sensor network is a collection of a large number of
sensor nodes that are deployed in a particular region.
Sensors are wirelessly connected and they, at appropriate times, relay
information back to some selected nodes.
These selected nodes then perform some computation based on the
collected data to derive an ultimate statistic to allow critical
decisions to be made.
There are a variety of sensors, including acoustic(sound related) ,
seismic (Subject to an earthquake or earth vibration), image, heat,
direction, smoke, and temperature sensors.
21
22. Basic features of sensor networks
A large number of low-cost, low-power, multifunctional, and small sensor
nodes
Sensor node consists of sensing, data processing, and communicating
components
A sensor network is composed of a large number of sensor nodes,
which are densely deployed either inside the phenomenon or very close
to it.
The position of sensor nodes need not be engineered or pre-determined.
sensor network protocols and algorithms must possess self-organizing
capabilities.
22
23. Basic features of sensor networks
Self-organizing capabilities
Short-range broadcast communication and multihop routing
Dense deployment and cooperative effort of sensor nodes
Frequently changing topology due to fading and node
failures
Limitations in energy, transmit power, memory, and computing
power
23
24. Wireless Sensor Networks
A sort of ad-hoc networks
A network of low cost,
densely deployed,
untethered sensor nodes
Application areas:
heath, military, and home
Placed in inaccessible terrains or disaster areas
It may be impossible to recharge batteries
Different Node Characteristics fromTraditional nodes
No of nodes in a sensor network can be several orders of magnitude higher than
the nodes in an Ad Hoc network (100s to 1000s nodes)
Densely deployed (20 nodes/m3)
Mobility of nodes is not mendatory
Prone to failures
Topology changes very frequently
Mainly use a broadcast communication, whereas most Ad Hoc networks are based
on point-to-point
Limited in power, computing capacities, and memory
May not have global ID because of the large amount of overhead and large number
of sensors
Ad Hoc Net
Wireless
Sensor
Network
24
25. Existing Wireless Net vs. Sensor Net
Cellular system Bluetooth, MANET Sensor Network
Single Hop Multi-hop Multi-hop
High QOS
Bandwidth efficiency
High QOS Power conservation
Limited bandwidth
Large number of node
Narrow radio range
Frequent topology change
Station to Base station Peer to peer
Peer to multi node
Peer to multi node
25
28. Sensor Networks Architecture
Sensor node
Made up of four basic components
Sensing unit, Processing unit,Transceiver unit, and Power unit
Additional application-dependent components
Location finding system, power generator, and mobilizer
Scattered in a sensor field
Collect data and route data back to the sink
Sink
Communicate with the task manager node (user) via Internet
or satellite
28
29. Components of Sensor Node
A sensor node is made up of four basic components
sensing unit
usually composed of two subunits: sensors and analog to digital converters
(ADCs).
processing unit,
Manages the procedures that make the sensor node collaborate with the other
nodes to carry out the assigned sensing tasks.
Transceiver unit
Connects the node to the network.
Power units (the most important unit)
29
30. Sensor network topology
Pre-deployment and deployment phase
Sensor nodes can be either thrown in mass or placed one by one in
the sensor field.
Post-deployment phase
Sensor network topologies are prone to frequent changes after
deployment.
Re-deployment of additional nodes phase
Addition of new nodes poses a need to re-organize the network.
30
32. Environment
Sensor nodes may be working
in busy intersections,
in the interior of a large machinery,
at the bottom of an ocean,
inside a twister,
in a battlefield beyond the enemy lines,
in a home or a large building
Transmission media
Industrial, scientific and medical (ISM) bands
offer license-free communication in most countries.
Infrared
License-free and robust to interference
requirement of a line of sight between sender and receiver
32
33. Micro-sensors
Uses
In military: surveillance and target tracing
health-care industry: allow continuous monitoring of life-
critical information.
food industry: biosensor technology applied to quality control
can help prevent rejected products from being shipped out,
Agriculture: help to determine the quality of soil and moisture
level; they can also detect other bio-related compounds.
Sensors are also widely used for environmental and weather
information gathering.They enable us to make preparations in
times of bad weather and natural disaster.
33
35. Wireless Mesh Networks
Mesh networking is the holy grail of wireless networking.
“Mesh” refers to many types of technology that enable
wireless systems to automatically find each other and self-
configure themselves to route information amongst
themselves.
35
36. 36
Wireless Mesh Networks
Mesh network implemented over
WLAN
“Mesh” refers to many types of
technology that enable wireless
systems to automatically find each
other and self-configure themselves to
route information amongst themselves.
Industrial standardsActivities
IEEE 802.11, IEEE 802.15, IEEE
801.16 have established sub-working
groups to focus on new standards for
WMNs
37. In a wireless mesh network, the network connection is spread out among
dozens or even hundreds of wireless mesh nodes that "talk" to each other
to share the network connection across a large area.
Mesh nodes are small radio transmitters that function in the same way as a
wireless router.
In a wireless mesh network, only one node needs to be physically
wired to a network connection like a DSL Internet modem.That
one wired node then shares its Internet connection wirelessly with all other
nodes in its vicinity.Those nodes then share the connection wirelessly with
the nodes closest to them.The more nodes, the further the connection
spreads, creating a wireless "cloud of connectivity" that can serve a small
office or a city of millions.
37
38. Wireless Mesh Networks
Possible deployment scenarios:
Residential zone : where broadband connectivity is required
Highway: where a communication facility for moving automobiles
is required
Business zones: where an alternative communication system to
cellular network is required
Important civilian regions: where a high degree of service
availability is required
University campus: where inexpensive campus wide network
coverage can be provided.
Operates at license-free ISM band -2.4 GHz and 5 GHz.
Speed - 2Mbps to 60 Mbps38
40. Benefits
Using fewer wires means it costs less to set up a network, particularly for large areas of coverage.
The more nodes you install, the bigger and faster your wireless network becomes.
They rely on the same WiFi standards (802.11a, b and g) already in place for most wireless
networks.
They are convenient where Ethernet wall connections are lacking -- for instance, in
outdoor concert venues, warehouses or transportation settings.
They are useful for Non-Line-of-Sight (NLoS) network configurations where wireless
signals are intermittently blocked. For example, in an amusement park a Ferris wheel occasionally
blocks the signal from a wireless access point.
Wireless mesh configurations allow local networks to run faster, because local packets don't
have to travel back to a central server.
Wireless mesh nodes are easy to install and uninstall, making the network extremely adaptable and
expandable as more or less coverage is needed.
40
41. Electric meters now being deployed on residences transfer their readings from
one to another and eventually to the central office for billing without the need
for human meter readers or the need to connect the meters with cables.
Mesh networks are "self configuring;" the network automatically incorporates a
new node into the existing structure without needing any adjustments by a
network administrator.
Mesh networks are "self healing," since the network automatically finds the
fastest and most reliable paths to send data, even if nodes are blocked or lose
their signal.
41
43. 43
Mesh vs. Ad-Hoc Networks
Multihop
Nodes are wireless, possibly
mobile
May rely on infrastructure
Most traffic is user-to-user
Ad-Hoc Networks Wireless Mesh Networks
Multihop
Nodes are wireless,
some mobile, some
fixed
It relies on
infrastructure
Most traffic is user-
to-gateway
44. 44
Mesh vs. Sensor Networks
Bandwidth is limited (tens of kbps)
In most applications, fixed nodes
Energy efficiency is an issue
Resource constrained
Most traffic is user-to-gateway
Wireless Sensor Networks Wireless Mesh Networks
Bandwidth is generous (>1Mbps)
Some nodes mobile, some fixed
Normally not energy limited
Resources are not an issue
Most traffic is user-to-gateway
47. 47
WMN Architecture
WMNs (Wireless Mesh Networks) consist of:
mesh routers and mesh clients
Mesh routers
Conventional wireless AP (Access Point) functions
Additional mesh routing functions to support multi-hop communications
Usually multiple wireless interfaces built on either the same or different
radio technologies
Mesh clients
Can also work as a router for clientWMN
Usually one wireless interface
Classification ofWMN architecture
Infrastructure/BackboneWMNs
ClientWMNs
HybridWMNs
50. 50
Hybrid WMNs
Wi-Fi, Wi-MAX,
Sensor Networks,
Cellular Networks, etc.
Internet
Wireless Mesh Clients
Wireless Mesh
Backbone
Conventional Clients
Mesh Router
Mesh Router
Mesh Router
with Gateway
Mesh Router
with Gateway
Mesh Router
with Gateway/Bridge
Mesh Router Mesh Router
Mesh Router
with Gateway/Bridge
51. Types of Ad Hoc Mobile
Communications
Mobile hosts in an ad hoc mobile network can communicate
with their immediate peers (peer-to-peer) that are a single
radio hop away.
If three or more nodes are within range of each other (but
not necessarily a single hop away from one another), then
remote-to-remote mobile node communications
exist.
Remote-to-remote communications are associated with
group migrations.
51
52. Types of traffic patterns in Adhoc
Ad hoc wireless communications can occur in several different
forms.
1) Peer-to-peer communication
Mobile host communicates in pair
For a pair of ad hoc wireless nodes, communications will occur
between them over a period of time until the session is
finished or one of the nodes has moved away.
2) Remote-to-remote communication
when two or more devices are communicating among
themselves and they are migrating in groups.
The traffic pattern is, therefore, one where communications
occur over a longer period of time.
52
53. Types of traffic patterns in Adhoc
3) Hybrid Communication
have a scenario where devices communicate in a non-
coherent fashion and their communication sessions are,
therefore, short, abrupt, and undeterministic.
MH: Mobile host
53
54. Types of Mobile Host Movements
Movements by Nodes in a Route
Movements by Subnet-Bridging Nodes
Concurrent Node Movements
54
55. Movements by Nodes in a Route
Source nodes
Downstream
link
Intermediate
nodes
Destination
nodes
Upstream
link
55
56. Cont…
An ad hoc route comprises the source (SRC), destination (DEST), and/or a
number of intermediate nodes (INs).
Movement by any of these nodes will affect the validity of the route.
An SRC node
has a downstream link, and
when moves out of its downstream neighbour's radio coverage range, the existing
route will immediately become invalid.
all downstream nodes may have to be informed so they can erase their invalid route
entries.
DEST node
moves out of the radio coverage of its upstream neighbour, the route becomes
invalid.
The upsteam nodes will have to be informed so they can erase their invalid route
entries.
IN node : any movement by an IN supporting an existing route may cause the
route to be invalid.
56
57. Movements cause many conventional distributed routing
protocols to respond in sympathy with the link changes.
Need to update all the remaining nodes within the network
so that consistent routing information can be maintained.
Updating process involves broadcasting over the
wireless medium, which results in wasteful bandwidth and
an increase in overall network control traffic. Hence, new
routing protocols are needed.
57
58. Movements by Subnet-Bridging Nodes
Subnet-bridging node movement
between two mobile subnets can
fragment the mobile subnet into
smaller subnets
Movements by certain nodes can
result in subnets merging (yielding
bigger subnets) while sometimes
subnet is partitioned by some subnet-
bridging mobile nodes
Updating all the nodes' routing tables
Choose to update only the affected
nodes' association tables.
58
59. Concurrent movements by nodes (SRC, DEST, or
INs)
Ensure there is consistency when multiple route
reconfiguration or repair processes are invoked.
Ultimately converge where the most appropriate
route reconfiguration is performed.
Concurrent Node Movements
59
60. 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)
60
61. Issues in Ad Hoc Networks
1. SpectrumAllocation and Purchase
2. Medium access scheme
3. Routing
4. Multicasting
5. Transport layer protocol Performance
6. Pricing shceme
7. QoS provisioning
8. Security
9. Energy management
10. Addressing and service discovery
11. Scalability
12. Deployment considerations61
62. 1. Spectrum Allocation and Purchase
FCC control the regulations regarding the use of radio
spectrum.
Who regulates the use of radio spectrum in INDIA??
To prevent 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.
62
63. 63
2.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
64. Media Access
TDMA and FDMA schemes are not suitable.
Many MAC (Media Access Control) protocols do not deal with host
mobility.
The scheduling of frames for timely transmission to support QoS is difficult.
In ad hoc wireless networks, since the same media are shared by multiple
mobile ad hoc nodes, access to the common channel must be made in a
distributed fashion, through the presence of a MAC protocol.
There are no static nodes, nodes cannot rely on a centralized coordinator.
The MAC protocol must contend for access to the channel while at the same
time avoiding possible collisions with neighboring nodes.
The presence of mobility, hidden terminals, and exposed nodes
problems must be accounted for when it comes to designing MAC
protocols for ad hoc wireless networks.
64
65. 65
Difference Between Wired and
Wireless
If both A and C sense the channel to be idle at the same time, they send
at the same time.
Collision can be detected at sender in Ethernet.
Half-duplex radios in wireless cannot detect collision at
sender.
A B C
A
B
C
Ethernet LAN Wireless LAN
66. IEEE has defined the specifications for a wireless LAN, called IEEE
802.11, which covers the physical and data link layers.
In IEEE 802.11, carrier sensing is performed
at the air interface (physical carrier sensing), and
at the MAC layer (virtual carrier sensing)
Physical carrier sensing
detects presence of other users by analyzing all detected packets
Detects activity in the channel via relative signal strength from other
sources
Virtual carrier sensing is done by sending MPDU duration information in
the header of RTS/CTS and data frames
Channel is busy if either mechanisms indicate it to be
Duration field indicates the amount of time (in microseconds) required to
complete frame transmission
Stations in the BSS use the information in the duration field to adjust their
network allocation vector (NAV)
802.11 - Carrier Sensing
66
67. A and C cannot hear each other.
A sends to B, C cannot receiveA.
C wants to send to B, C senses a “free” medium.
Collision occurs at B.
A cannot receive the collision.
A is “hidden” for C.
Hidden Terminal Problem
BA C
67
68. Exposed Terminal Problem
A starts sending to B.
C senses carrier, finds medium in
use and has to wait for A->B to
end.
D is outside the range of A,
therefore waiting is not necessary.
A and C are “exposed” terminals
A B
C
D
68
69. 69
3. 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
~ 10-3
wireless vs. 10-12
~ 10-9
wired
Location-dependent contention
Distribute load uniformly
70. Routing
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 needed70
71. Routing protocols
Routing protocols
Purpose is to dynamically communicate information about all
network paths used to reach a destination and to select the from
those paths, the best path to reach a destination network.
Types of routing protocol
Distance –vector Routing Protocol
Distance vector protocols use a distance calculation (distance metric) plus
an outgoing network interface (a vector) to choose the best path to a
destination network.
The network protocol (IPX, SPX, IP,Appletalk, DECnet etc.) will forward
data using the best paths selected
Well Supported Protocols such as RIP have been around a long time and
most, if not all devices that perform routing will understand RIP.
71
72. Link state based
Selects the best routing path by calculating the state of each link
in a path and finding the path that has the lowest total metric to
reach the destination.
Link State protocols track the status and connection type of
each link and produces a calculated metric based on these and
other factors, including some set by the network administrator.
Link state protocols know whether a link is up or down and
how fast it is and calculates a cost to 'get there'.
Link State protocols will take a path which has more hops, but
that uses a faster medium over a path using a slower medium
with fewer hops.
72
73. Difference
If all routers were running a DistanceVector protocol, the path or
'route' chosen would be from A B directly over the ISDN serial link,
even though that link is about 10 times slower than the indirect route
from A C D B.
A Link State protocol would choose the A C D B path because it's
using a faster medium (100 Mb ethernet).
In this example, it would be better to run a Link State routing protocol,
but if all the links in the network are the same speed, then a Distance
Vector protocol is better.
73
74. 74
Routing (2)
Requirements
Minimum route acquisition delay
Quick route reconfiguration
Loop-free routing
Distributed routing approach
Minimum control overhead
Scalability
QoS provisioning
Support for time-sensitive traffic
Security and privacy
75. 4. Multicasting
Multiparty communcations are enabled through the
presence of multicast routing protocols.
The multicast backbone (MBone) comprises an
interconnection of 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.
75
76. 76
Multicasting
Robusteness
recover and reconfigure quickly from potential mobility-
induced link breaks
Efficiency
Min control overhead
QoS support
Efficient group management
Scalability
security
77. 5. Energy Efficiency
Mobile devices today are mostly operated by batteries. Battery
technology is 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.
77
78. 78
Energy Management
Tx power mgmt
MAC: sleep mode
Routing: consider battery life time: load balancing
Transport: reduce ReTx
App
Battery energy mgmt
Extend battery life by taking adv of chemical properties,
discharge patterns, and by the selection of a battery from a set
of batteries
Processor power mgmt
Device power mgmt
79. 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.
79
80. TCP relies on measuring the round-trip time (RTT) and packet loss
to conclude if congestion has occurred in the network.
In telecommunications, the round-trip delay time
(RTD) or round-trip time (RTT) is the length of time it takes for
a signal to be sent plus the length of time it takes for an
acknowledgment of that signal to be received.This time delay
therefore consists of the transmission times between the two points of
a signal.
TCP is unable to distinguish the presence of mobility and
network congestion.
Mobility by nodes in a connection can result in packet loss and long
RTT.
Enhancements needed to ensure that the transport protocol performs
properly without affecting the end-to-end communication throughput.80
81. 7. Service Location, Provision, and
Access
Ad hoc 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.
81
82. 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 paket and the flow ID or label.
82
83. 83
Security
DoS attack
Resource consumption
Energy depletion
Buffer overflow
Host impersonation
Information disclosure
Interference
84. 84
9. Deployment Consideration (1)
Adv. in ad hoc net
Low cont of deployment
Incremental deplyment
Short deplyment time
Reconfigurablity
Scenario of deployment
Military deployment: data-centric or user-centric
Emergency operation deployment: hend-held, voice/data,
< 100 nodes
Commercial wide-area deployment: e.g.WMN
Home network deplyment
85. 85
Deployment Consideration (2)
Required longevity of network
Area of coverage
Service availability: redundancy
Operational integration with other infrastructure
Satellite network, UAV(unmanned aerial vehicles), GPS
Cellular network
Choice of protocols
TDMA or CSMA-based MAC?
Geographical routing (using GPS)
Power-saving routing ?
TCP extension ?
