Thesis

TECHNOLOGY CHALLENGES FOR CONTEXT AWARE
MULTIMEDIA SERVICES
by
Suneth Namal Karunarathna
A thesis submitted in partial fulﬁllment of the requirements for the
degree of Master of Engineering in
Information and Communication Technologies
Examination Committee: Dr. R.M.A.P. Rajatheva (Chairman)
Associate Prof. Tapio J. Erke
Dr. Matthew N. Dailey
Nationality: Sri Lankan
Previous Degree: Bachelor of Science in Computer Engineering
University of Peradeniya
Peradeniya, Sri Lanka
Scholarship Donor: The Government of Finland
Asian Institute of Technology
School of Engineering and Technologies
Thailand
May 2010
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ACKNOWLEDGEMENT
First of all it is my pleasure to express sincere regards to my thesis advisor, Dr.
R.M.A.P. Rajatheva for the guidance, encouragement and tremendous help throughout
the whole two years of my study. His encouragement and guidance made me to start my
research work beginning of the inter-semester while setting more chances to familiarize
with the work. His sound knowledge and the experience in the field was the fact behind
motivation during my study.
My special thanks must go to examination committee member Associate Professor
Tapio J. Erke for the guidance and the corrections of my proposal. Further, I am thank-
ful to the Assistant Professor in the Computer Science and Information Management
program Dr. Matthew N. Dailey for being in my examination committee.
I would make this an opportunity to thank my scholarship donors, Government of
Finland and Institute Telecommunication for supporting me financially. It brought me
success in academic life investigating my capabilities and creativity during past two
academic years.
I am grateful to Dr. Gyu Myoung Lee being my advisor at Institute Telecom-
munication, France. Further, my special thanks must goes to Prof. Noel Crespi the
program director of Master of Science in communication network. His timely decision
to select me to the dual degree program brought me lot of opportunities to explore real
industry environment and the new technologies.
Many thanks to Mr. Keeth Saliya, Mr. Shashika Manosha, Mr. Madushan Thilina
and Mr. Sanjeewa Herath for the support in both academic and day today life during
the stay in AIT. And I value the friendly discussions we had together regarding aca-
demic matters and the contributions to each others work. All the academic staff and
administrative personnel, specially senior lab supervisor , Mr. Rajesh Kumar Dehury,
TC secretaries, Mrs. Nantawan Nakasen, Miss. Chutikarn Kridsadavisakesak and Mr.
Jaruk Noonkhao are thankfully admired for immense help in all many ways during my
stay.
Finally, I will make this an opportunity to avail the gratitude to my beloved
parents for everything they have done for me. And I dedicate this thesis dissertation
to my parents.
ii

ABSTRACT
This work presents an effort on quality improvement in the existing multimedia
services. It is identified that the multimedia services are more sensitive on certain
parameters which significantly degrade the service quality in the target domain. The
issues related to the multimedia services are discussed and ways presented to maximize
the end-user satisfaction in a focused environment. The effects of context reasoning in
the evolutionary multimedia applications are observed and a novel context reasoning
scheme based on AHP is proposed to utilize the processing power. Interestingly, the
nature of AHP is based on the pare-wise attribute comparison in the proposed home
environment. In addition to that, it is found that the service response time and the
blocking probability have notable effects on the user experience. Hence, two evalua-
tion models are developed to observe the performance level in terms of all the above
parameters at the target scenario. Moreover, two hierarchical proxy architectures are
defined and the results are compared with an ideal case where no proxy servers are
deployed in the network. The evaluation process in terms of the service continuity gives
rise to the investigation of the blocking probability. Thus, the demand for the system
resources is presented with a general birth-death process in the proposed analytical
model. In addition to that the importance of reliable and accurate context informa-
tion is identified and a novel scheme for anomaly detection is presented based on the
rate and power anomaly detection. Moreover, the detection probability is measured
for Gauss-Markov mobility model and compared with an ideal simulation model based
on the Random-Waypoint. Overall, the study contributes to maximize the quality of
service in a multimedia service environment.
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Table of Contents
Chapter Title Page
Title Page i
Acknowledgement ii
Abstract iii
Table of Contents iv
List of Abbreviations vi
List of Tables vii
List of Figures viii
List of Symbols xi
1 Introduction 1
1.1 Context Awareness and Context Reasoning 1
1.2 Technology Evolution in Multimedia Applications 1
1.3 Hierarchical Analytical Process 2
1.4 Intrusion Detection in Sensor Networks 2
1.5 Objective of Study 3
1.6 Scope and Limitations of Study 4
1.7 Organization of the Thesis 4
2 Technology Challengers for Multimedia Services 5
2.1 User-Driven Ubiquitous Networking Environment 5
2.2 Requirement for Seamless Multimedia Services 6
2.3 Challenging Technologies for Ubiquitous Multimedia Services 8
2.3.1 Service Continuity 9
2.3.2 Context Awareness in Multimedia Applications 10
2.3.3 Content Delivery in Ubiquitous Environment 13
2.3.4 Cross-Layer Adaptation for Multimedia Applications 14
2.4 Mobile IPTV Service in Ubiquitous Networking Environment 17
2.5 Threats Over Context Collectors 18
2.5.1 Limited Resource Constrain of Sensors 18
2.5.2 Communication Unavailability 20
2.5.3 Unattended Operation 20
2.6 Security Concern of Sensors 20
2.7 Attacks on Wireless Sensor Networks 21
2.7.1 Attacks on Data Link Layer 21
2.7.2 Attacks on Network Layer 22
2.7.3 Log-distance Path Loss Model 24
2.8 Mobility Models for Sensor Nodes 24
3 Context Reasoning in context aware Multimedia Services 27
3.1 Introduction 27
3.2 Technical challenges in Context Reasoning 27
3.3 Analytic Hierarchical Process in Context Reasoning 30
iv

3.4 Proposed Model for Context Reasoning 31
3.5 Conclusion 37
4 Performance improvement in multimedia services 38
4.1 Introduction 38
4.2 Proxy Architecture and Cache Arrangement 38
4.3 Mathematical Analysis of Response Time 40
4.3.1 Proposed Proxy Architecture 40
4.3.2 Existing Models in Performance Evaluation 41
4.3.3 Proposed Model for Response Time Measurement 42
4.3.4 Simulation Results Obtained with Proposed Model 46
4.4 Seamless service Continuity in Multimedia Service 53
4.4.1 Analytical Model for Proxy Handover 53
4.4.2 Analytical Results Obtained with Deﬁned Model 56
4.5 Conclusion 61
5 Secure Context Gathering for Context Reasoning 62
5.1 Introduction 62
5.2 Baseline Approach to Anomaly Detection 62
5.2.1 System Model for Baseline Approach 62
5.2.2 Modiﬁed Detection Algorithm 63
5.2.3 Sensing Model and the Detection Algorithm 66
5.2.4 Simulation Results of the Proposed Model 72
5.3 Conclusion 77
6 Conclusion and Recommendations 78
6.1 Conclusion 78
6.2 Recommendations 79
References 80
APPENDIX A 84
APPENDIX B 92
v

List of Abbreviations
BS Base Station
CDN Content Delivery Network
CDS Content Delivery System
GRAB Gradient Broadcast Routing
GEAR Geographical and Energy Aware Routing
GAF Geographic Adaptive Fidelity
GPSR Greedy Perimeter Stateless Routing
IDS Intruder Detection System
LEACH Low Energy Adaptive Clustering Hierarchy
MANET Mobile Ad-hoc Networks
MS Mobile Station
OSI Open Standard Interconnection
PDA Personal Digital Assistance
RFID Radio Frequency Identiﬁcation
RTS Request To Send
SPINE Secure Positioning for Sensor Networks
SMIL Synchronized Multimedia Integration Language
TTDD Two-Tier Data Dissemination
WSNs Wireless Sensor Networks
vi

List of Tables
Table Title Page
3.1 Calculation of attribute comparison matrix 33
3.2 Calculation of priority vector 34
3.3 Example for calculating attribute comparison matrix 35
3.4 Example for calculating option comparison matrix 35
3.5 Calculation of composite matrix using attribute and option com-
parison matrix 35
4.1 List of parameters bring used in the simulation 46
4.2 Parameters used in the analytical model for evaluating call blocking
probability 54
5.1 IDS parameter list used in mathematical simulation 65
5.2 Parameters being used for the simulation purpose 72
vii

List of Figures
Figure Title Page
2.1 Ubiquitous networking service environment ensures the service con-
tinuity regardless of mobility pattern or user behavior 6
2.2 Multimedia content delivery system in ubiquitous networking envi-
ronment for seamless service availability 8
2.3 Seamless service continuity in user-driven ubiquitous networking
environment guarantees service access irrespective of user context 9
2.4 Context aware applications are responsible for self determination
of communication technique and the suitable terminal with proper
media format and codec 11
2.5 Ontology based context reasoning scheme (Wei and Chan, 2010) 12
2.6 IPTV content delivery in ad-hoc service environment providing
platform independent service environment 14
2.7 Multimedia adaptation middle-ware platform which controls the
media characteristics to format the content to fit the end user requirements 15
2.8 Service scenario in home environment for seamless service accessi-
bility over different end user terminals 17
2.9 Mobility pattern of a sensor node when routing is simulated with
Random-Waypoint model 26
2.10 Mobility pattern of a sensor node when routing is simulated with
Gauss Markov model 26
3.1 User context management in ubiquitous home environment which
support seamless service availability. This figure shows the exis-
tence of different devices inside home and how they are connected
to home gateway or the set-top-box for content divergence 28
3.2 Unicast and multicast traffic in IPTV services. Liner TV stream
always broadcast reserving fixed bandwidth for each channel. On
the contrary, VoD and time shift TV assign an individual stream
for each connected user 29
3.3 This figure explains decision-making process in context reasoner at
a home environment. Context information is gathered by the sen-
sors around user and sent to the context reasoner which is located
in home network or operator network 31
3.4 Expanded partial tree for device selection. This partial tree in-
cludes preference for each device and score assigned to each property 32
4.1 Service request procedure. Transmission path is divided in to two
core network path and access network path. Proxy server supports
to achieve CBR type of transmission over core network 39
4.2 Hierarchical proxy architecture. Considered architecture has a hi-
erarchical caching system where contents are stored in different tiers 40
4.3 Target proxy architectures for response time measurement 41
4.4 Model defined to measure the service response time (Nikolov, 2009) 42
viii

4.5 Model for performance evaluation of hierarchical proxy architec-
ture. For this model, content is cached to different tiers with re-
spect to their popularity, size and many other factors. (The dotted
line shows the requests missed by proxy server) 43
4.6 Response time vs. arrival rate for architecture 1, architecture 2 and
no proxy architecture. Here we consider multimedia type of traffic
while limiting hierarchy to single tier (n=1) 47
while limiting hierarchy to two tiers (n=2) 48
while limiting hierarchy to three tiers (n=3) 49
4.9 A comparison of lowest Response time towards Arrival rate for
different n. Architecture 2 gives the best response time in all cases
for multimedia based traffic 50
no proxy architecture. Here we consider web based traffic while
limiting hierarchy to single proxy level (n=1) 50
limiting hierarchy to two tiers (n=2) 51
limiting hierarchy to two proxy tier (n=3) 51
4.13 A comparison of least response time towards arrival rate for differ-
ent n. Architecture 2 gives the best response time in all cases for
web based traffic 52
4.14 Target environment for service handover for mobile multimedia ser-
vice users 53
4.15 Call arrival model 55
4.16 Queuing model for proposed system 56
4.17 Blocking probability Vs number of total channels in proxy server 57
4.18 Blocking probability Vs number of total channels in proxy server
for different λt 58
4.19 Blocking probability Vs number of total channels in proxy server
for changing number of reserved channels in server side for handover calls 59
4.20 Blocking probability Vs λh for changing number of exclusively re-
served channels in the server 59
4.21 Probability of not having a slot in the queue Vs λh for changing
number of exclusively reserved channels in the server 60
5.1 Block diagram of power anomaly detection module which detects
nodes transmit above defined threshold 64
5.2 Block diagram of network unavailability detection module which
measures transmission attempts of legitimate nodes 65
5.3 Effect of intruders in a wireless sensor network 67
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5.4 Power anomaly detection procedure in proposed detection architecture 68
5.5 Rate anomaly detection procedure in proposed detection architecture 69
5.6 Detection probability against transmit power level for two deﬁned
mobility models Random-Waypoint and Gauss-Markov keeping other
variables constant 73
5.7 Detection probability against transmit power level for Random-
Waypoint mobility model for changing speed, 1ms−1
,5ms−1
,10ms−1
74
5.8 Detection probability against node speed for Random-Waypoint
mobility model for changing transmit power levels, 5dBm, 10dBm,
15dBm 74
5.9 Detection probability against transmit power level for Gauss-Markov
mobility model for changing speed, 1ms−1
,5ms−1
,10ms−1
75
5.10 Detection probability against node speed for Gauss-Markov mobil-
ity model for changing transmit power levels, 5dBm, 10dBm, 15dBm 75
5.11 Detection probability against transmit power level for changing sen-
sitivity parameter while keeping all other variables constant for
Random-Waypoint mobility model 76
5.12 Detection probability against transmit power level for changing sen-
sitivity parameter while keeping all other variables constant for
Gauss-Markov mobility model 76
A.1 Power anomaly detection probability towards transmit power level
for changing frame sizes 84
A.2 Power anomaly detection probability towards transmit power level
for nodal speed 85
A.3 Average detection time towards transmit power level for changing
frame sizes 86
A.4 Congestion probability towards transmit power level for changing
radio range 87
A.5 Congestion probability towards transmit power level for changing
nodal speed 88
A.6 Block diagram for response time measurement 89
A.7 Block diagram for blocking probability measurement 90
A.8 Analytic model to evaluate blocking probability 91
x

List of Symbols
Pi Property i
Oi Option i
Si Score assigned to property i
Di Percentage on device preference
pij property i relative to j
Pij Normalized pij
Ptransmit Transmit power
Preceived Received power
σ Standard deviation
pb Blocking probability
K Buffer of capacity K
Vt Velocity at time t
θt Angular velocity at time t
A Total coverage area by sensors
Rij Packet rate at node i compared to node j
λa Arrival rate on proxy server
Pa Hit rate of the proxy server
Ip Lookup time for proxy server
Is Lookup time for proxy server
F Average file size
BWp Client network bandwidth
BWs Operator network bandwidth
Bs Server buffer
Bp Proxy buffer
ts Static time for head-end
tp Static time for Proxy
λt Total call rate in a cell
λh Handover call rate
xi

λs call rate generated by stationary users
λc Carried call rate
λm New call rate by mobile users
Nh Exclusively reserved channels for handover users
Ploss Probability of not having a position free for handover call
PfhA Handover failure even with free positions in queue
Pdrop Probability of call drop for mobile and stationary users
Phv Call in progress will required a handover for vehicular user
PBA Call Blocking probability for stationary and mobile users
µc Call completion rate
µv Handover departure rate for vehicular calls
µq Rate at which being in an overlapping area
Tc Average call duration for any user
Tv Mean sojourn time for vehicular users
Tq Average time duration MS reside in an overlapping area
γ1 Probability that served call due to ﬁrst stream
γ2 Probability that served call due to second stream
xii

CHAPTER 1
INTRODUCTION
1.1 Context Awareness and Context Reasoning
The evolution of the mobile technology facilitates the humanity with fascinating con-
text aware applications in to hand-held devices like PDAs, Ipods and laptops. React
according to the context being experienced by the users is found to be the key feature
of the context aware application. In other words, services are changing their signifi-
cant parameters according to the user context, to adapt to the current environment
(Khedo, 2006). These contexts can be emotions, physical activities or environmental
factors such as location, time, temperature, pressure or humidity (Pavel and Trossen,
2006). In order to make such systems effective, sensors have to capture the data which
is accurate and reflects real-time situations and events (Godbole and Smari, 2006). In
some cases, prototypes are required for collecting context data which are not readily
available (Kerpez et al., 2006). Thus, the presence of inaccurate context data causes
low performances and inefficiency of the system. It is noteworthy to point out that, the
ultimate goal of context aware applications is achieved by adapting to the environment
with proper user interfaces and services considering the user context profile.
As an instance, we can consider a situation where a user is going to the super
market with a mobile. It can be used as a device which helps him to select the goods
which he is intending to bring back to the home. Further, it can suggest some other
items which he may prefer to purchase. Moreover, he will receive a detailed description
of the products to be purchased and options or substitutions for missing items. Finally,
at the end of the day it will display the shortest route to return home. This scenario
simply explains the context awareness.
The received context awareness information through the sensors, adapt the appli-
cations to match the current environment settings (Wang, 2004). But, there should
be an intermediate module which evaluates these information and makes decisions.
These modules are introduced as the context reasoner (CR) in literature (Pavel and
Trossen, 2006; Godbole and Smari, 2006; Wang, 2004). The context reasoner obtains
the inputs from sensors and handovers it to the evaluation scheme, which is probably
a rule based evaluation module (Docter et al., 2007). According to the results of the
context reasoner, the service or the device itself adjusts to fit the user context without
any human interaction (Wang, 2004).
1.2 Technology Evolution in Multimedia Applications
Multimedia applications are quite sensitive to delay, jitter and packet loss situations.
Thus these factors significantly degrade the quality of the services (Menai et al., 2009).
Therefore, it is a challenging issue to reduce the service delay or the response time
(Docter et al., 2007). More significantly, present multimedia applications are capable
of service adaptation depending on the user context for delivering a better experience
to the end users (Hsiao et al., 2008).
But, the whole process of context evaluation depends on sensors which collect and
1

aggregate contextual information. As we already mentioned above, delay is the most
critical issue related to the multimedia services. To overcome this problem, operators
use proxy servers in their networks. The operators further reduce the response time
by means of distributed content management techniques. Multimedia applications like
IPTV, VoD and time shift TV integrate many other services together and presented in
a single package to the subscribers (Menai et al., 2009). In terms of content delivery,
researches have taken a great effort to reduce the bandwidth usage by introducing
compressed media formats. There is always a trade-off between channel bandwidth
and the quality of the service (Bellinzona and Vitali, 2008). Therefore, maintaining
the service while reducing per user bandwidth is a challenge towards the operators.
Novel video formats are capable of performing this task much better (Hsiao et al.,
2008). But, the costly bandwidth still demands capacity optimization techniques in
the networks to utilize the bandwidth and other resources.
1.3 Hierarchical Analytical Process
Analytic hierarchical process (AHP) is a mathematical model which simplifies the ob-
jectives and selects the most suitable alternatives in the real environment (Zahedi,
1986). AHP contributes in decision making, to find the best option standing on their
understanding level of the problem (Pavel and Trossen, 2006). In many engineering
applications we can use AHP as a powerful tool for object comparison (Pawar et al.,
2008). By introducing the pair-wise matrix comparison, the AHP gives the relative im-
portance of the options or alternatives compared to others. Irrespective of the field, this
technique can be used in any area like industry, health care and business environment
(Loke, 2006).
AHP models the target scenario in a hierarchy which decomposes the main problem
into sub-problems. In a hierarchical architecture, the complete solution can be obtained
by solving each sub problem separately. After building the hierarchy, evaluation could
be done systematically in order to compare elements. Because of the ability to convert
practical problems in to numerical models, AHP could be used in context evaluation
(Balasubramaniam and Indulska, 2004). Further, it allows to weight over the significant
elements depending on the preference (Loke, 2006).
1.4 Intrusion Detection in Sensor Networks
Wireless sensor networks (WSNs) are susceptible to many form of attacks due to the
resource constraints and the unsecured environment in which they have been deployed
(Onat and Miri, 2005). The broadcasting nature of the WSNs makes it more vul-
nerable to attacks. Most of WSNs are application oriented. That means they have
specific characteristics to perform a predefined set of tasks (Pires Jr et al., 2004). This
restricts developing a general platform for intrusion detection. All security solutions
for the sensor networks or ad-hoc networks could be divided in to two classes namely;
prevention techniques and detection techniques (Silva et al., 2005). Limited resources
and low computation capability in sensor networks pose many challenges in terms of
network security.
WSNs can have one or more central nodes called as base stations (BS). They
2

perform the gateway operation while providing the storage and data processing func-
tionality on behalf of other nodes. Due to powerful data processing and aggregation
capabilities, the base stations operate as a human interface to perform administrative
functions (Ilker and Ali, 2005). If the BS fails due to some reason, data aggregation
and detection capabilities could be reduced or stopped (Liu et al., 2004). From an
adversary’s point of view it is quite easy to find the location of the BS by looking
at the traffic pattern and hence to physically damage it. This might result to reduce
throughput or eliminate the entire communication with the BS. Denial of service (DoS)
attack is one of the most common attacks over WSNs which makes the resources un-
available to intended users. Therefore, it is important to come up with an Intrusion
Detection Scheme (IDS) which efficiently utilizes resources since WSNs have scarce
resources (Hamid et al., 2006). This fact encourages the researchers to develop power
based connectivity concept which reduces the average power consumption of the sensor
networks.
Collection and organization of context information is an important consideration
in context aware services (Elias et al., 2007). The performance of a context evaluation
scheme depends on the reliability of gathered information. Sensors are widely used to
capture the context. They are autonomous devices having low processing power with
less energy consumption. Because of this nature they are more reluctant to different
forms of attacks (Chen et al., 2009). Rather, it is difficult to implement heavy security
mechanisms over these devices due to low computation capabilities. This demands for
light weight effective security schemes to be implemented over sensors.
1.5 Objective of Study
This thesis analyzes technology challenges in context aware multimedia services. The
objectives are as given below.
1. Conduct a survey on challenging technologies for multimedia services in user-
driven ubiquitous networking environment.
2. Developing a light weight context reasoning scheme at home environment for
multimedia services based on AHP.
3. Developing a performance evaluation scheme for multimedia services.
(a) Measure the performance in terms of the response time with a defined ar-
chitectures and compare it with no proxy architecture.
(b) Measure the performance in terms of call blocking probability for a multi-
media subscriber under dynamic system conditions.
4. Developing a scheme for secure context gathering
(a) Developing a scheme based on power and rate anomaly detection
(b) Measure the performance in terms of detection probability for different mo-
bility models.
i. Measure detection probability for Random-Waypoint mobility model.
ii. Measure detection probability for Gauss-Markov mobility model.
3

iii. Compare detection probability of the proposed scheme with an ideal
case.
1.6 Scope and Limitations of Study
1. All the analysis are applicable for multimedia type of applications.
2. The clients are assumed to be knowledgeable enough to decide their preference
compared to each other.
3. Consider a single server with a buﬀer of length K for blocking probability mea-
surement.
4. User devices are capable of deciding the basic context.
1.7 Organization of the Thesis
The rest of the thesis is organized as follows. Chapter 2 provides a general litera-
ture review of the research area exploiting the technical challenges of context aware
multimedia services.
Chapter 3 discusses context reasoning in context aware multimedia services at
home environment. The section 3.4 presents the proposed context reasoning model.
The challenges in context evaluation and use of AHP in context reasoning are addressed
in sections 3.2 and 3.3. The chapter 4 presents detailed performance evaluation in
multimedia service in terms of response time and blocking probability. Section 4.3
proposes an analytic model for response time measurement. The model deﬁned to
measure blocking probability is presented in section 4.4.
In chapter 5 we discuss secure context gathering with sensors. The section 5.2.2
presents a baseline approach for intrusion detection. The proposed anomaly detection
scheme is presented in section 5.2.3 The conclusion and the recommendation presented
in Chapter 6.
Finally, in the appendix A we include some graphs obtained for the model discussed
in section 5.2.2.
4

CHAPTER 2
TECHNOLOGY CHALLENGERS FOR MULTIMEDIA SERVICES
2.1 User-Driven Ubiquitous Networking Environment
Over the past two decades context awareness has greatly evolved from its location
awareness roots to include properties such as situation, emotions, user and environ-
mental properties, and so on (Pavel and Trossen, 2006). Technologies like sensors,
machine learning algorithm, data mining tools evolves to generate contextual data
such that application developers can use them more intelligent and effective manner.
The improvement of technology brings many challenges in the field of communication.
As a result applications are getting more and more complicated day by day. The intro-
duction of mobility in to communication makes it more vulnerable in terms of quality
assurance. But, later on services were developed to dynamically adapt the user context.
We can consider such context change as a change in user location, his/her emotions,
environmental conditions or physical fact. Adaptability of services and applications are
recognized as one of the most important characteristics for future systems (Godbole
and Smari, 2006). Therefore, the developing ubiquitous context aware systems using
context data is a challenging task in future applications. Managing the user context
in more intelligent and effective manner is the biggest challenging issue for application
developers. However, this brings a good opportunity for both researchers and applica-
tion developers to pay their attention on context adaptation. Combination of context
adaptation with content delivery in mobile environment tremendously increases the us-
ability of services and devices. In context aware system design, sensors are the primary
means for data acquisition.
Increasing number of the mobile devises collaborate with the context awareness
improve the usability of newly developed systems while accomplishing every day activi-
ties which are carried out on move (Khedo, 2006). In mobile and ubiquitous computing
environment anticipation of reaction to the users expectation highly depends on the
context of use, events, as well as prior experiences. We could say any system to be
context aware if it capture, interpret and manage the context data to adjust the sys-
tem functionalities to suit the existing context. Still there are open issues in managing
complexity like gathering, processing and representing context data.
Ubiquitous networking suggests back-end model of processing information from
objects and human activities daily encounter in their life. The term ubiquitous implies
fact that connectivity or the technology is everywhere and that could be accessed
irrespective of location or the time. Basically, ubiquitous networking has two behaviors
like fixed to mobile and mobile to mobile. In either model, devices are mesh networked
allowing seamless access to different services and information. In ubiquitous networking
environment (see Fig. 2.1), all devices are connected to distributed servers which are
somehow connected to each other and make decisions according to input information.
Usage of micro devices placed over public and private places communicates each
other and gather context information from the service environment via the sensors
deployed in the field. Further, it enables connection of all devices together in to a
single network where they can communicate each other seamlessly. Advancement in
communication and computing together with new technologies does many changes in
5

Figure 2.1: Ubiquitous networking service environment ensures the service continuity
regardless of mobility pattern or user behavior
living environment. Basically, the concept of ubiquitous networking facilitates human
life changing vision of the environment. However, ubiquitous networking significantly
differs from any other kind of traditional networks due to their seamless availability.
In terms of home networking system, users suppose to have a good interaction and
better understanding of each other to sophisticate their fundamental needs. Further,
individuals can use different devices, technologies and adaptation techniques in various
environments to access the services in ubiquitous environment. These devices could be
used to access service information as user preference.
In ubiquitous environment user satisfaction is realized with smooth real time infor-
mation access regardless of user context or the access content. Ubiquitous networking
limits the user performances due to computational and processing power of the con-
nected terminals, which we call the heterogeneity of the network. Since, these devices
have different capabilities the requirement of common platform arises. This is one of
the biggest challenges in existing ubiquitous networks.
Serving individual terminals with different capabilities request specific protocols
to occupy in the networks to make it efficient and robust to compatible with different
terminals. Generally in sensor and home networks we find lot of devices which operates
on heterogeneous environment. With the increment of number of heterogeneous termi-
nals in the ubiquitous environment needs more service adaptation, media adaptation
and robustness to provide better service over the ubiquitous environment.
2.2 Requirement for Seamless Multimedia Services
The advancement of technology results the development of many services over the tra-
ditional communication network. Services like IPTV, Mobile TV, High Definition -
TV intergraded with many other services makes subscribers to access and shift be-
tween different services. Improvement in technologies like media adaptation, channel
6

adaptation, cross-layer adaptation assures seamless accessibility. IPTV is one of the
interesting services provided over the traditional communication network which is inte-
grated together with many other value added services. The latter development fallows
transferring media content from television to mobile devices like PDAs, mobile phones
or laptops. This introduces the concept of Content fallowing you while enabling seam-
less service accessibility.
Service continuity is another important quality constrain in modern communica-
tion. This guarantees users will have the seamless access to service and the contents.
For an example, we consider a person who just finishes his work at office. During his
travels on the bus or the train he can access the work that he was doing at the office
and finish it along the way. Once he gets down, he will go to the nearest supermarket
and download the item list over the Internet to be taken to home. And he will pay the
items on-line over the internal Wi-Fi network with his PDA inside the supermarket.
This scenario provides a good example for seamless service continuity.
Service continuity assures the service will not get obstruct by the user localization
or the access mechanism. Basic idea of service continuity implies few important facts.
This relies on the seamless service coverage regardless of platform or content type. This
rapidly growing momentum behind multimedia content delivery merged to the content
adaptability or the scalability. Delivering compatible contents to heterogeneous devices
is a challenging issue for service providers. Generally, context awareness is an abstract
model behind the application which makes decisions to deliver the best content with
the best quality to subscribers.
For an example, when a person entering to his home the songs we was listening in
his iPod will immediately transferred to home theater and the iPod will automatically
go in to sleep mode. Meantime, the home theater will itself adjust the tempo and
equalizer settings to feel him the best experience. Context aware devices or the appli-
cations always keep track on context of use. And whenever they request service this
information is sent attached with the request. Then the source will query the contents
from the best possible content providers considering received information. Next, the
selected content required to deliver towards the destination.
Content delivery network (CDN) or content delivery system (CDS) does this on
behalf of the subscribers or the user. Generally this delivery is done over transmission
control protocol (TCP) or user datagram protocol (UDP) connections. However, the
performances in TCP session can hardly affected with packet loss or the delay. The
stream control transmission protocol (SCTP) shares features of both of TCP and UDP.
SCTP transmit data over chunk with a header. Then these chunks are bundled to
SCTP packets and handover to Internet Protocol.
Packet loss and delay hardly affect to the user experience. To minimize this effect
sources or the media content servers are placed closer to edges. Distributed content
servers can also improve the delivery performances. We can find there are three dom-
inant content delivery systems as World Wide Web (WWW), network providers net-
works and Peer-to-Peer sharing systems. Even though they are being used for the same
purpose still the system architectures are quite different from each other. Fig. 2.2,
shows us how the media content is delivered over the access network. Normally, most
of the multimedia contents are transported as broadcast traffic. However, most of lat-
est researches targets on introducing unicast traffic model to replace broadcast traffic.
This is found to be more complex and need more processing power and resources.
7

Figure 2.2: Multimedia content delivery system in ubiquitous networking environment
for seamless service availability
Maintaining sustainable end-to-end quality over network throughout whole du-
ration of transmission is a challenging concern for network providers. The solution
requires interaction between different elements and layers. Even though, the initial
adaptation technologies are limited into single layer, now researches are more concern
in finding global optimal solution for cross layer adaptation.
It increases the interaction among different layers to maximize the quality of ex-
perience and minimize the service deployment cost in service providers perspective.
Compared to wireless networks wire networks offer many opportunities providing bet-
ter quality of experience (QoE) and exploding variety of services. Considering the
fallowing facts we find the requirement for cross layer adaptation. Perfect network
status measurement involves observation of different layer parameters and merge them
together in to one model.
In the context of services or content adaptation, cross layer adaptation can play a
key role to handle enormous dependencies arise due to heterogeneity. Characteristics of
wireless channels like higher packet loss ratio, signal-to-noise ratio (SNR), bit error rate
(BER) implies the requirement for better adaptation between different communication
layers to minimize the loss. Further, cross layer optimization can help to provide
smooth transmission over best effort infrastructure like WWW.
2.3 Challenging Technologies for Ubiquitous Multimedia Services
The technology used in multimedia services has vastly changed during the past decade.
Delivering continuous and smooth media stream over wireless link is a challenging task
due to continuous change in channel properties over the time. The unpredictable behav-
ior of wireless communication resulted in developing the concept of adaptation. Ubiq-
8

uitous computing has become a major concern in many of the scientific researches due
to advancement in communication architectures like next generation network (NGN),
universal mobile telecommunications system (UMTS), IP multimedia subsystem (IMS)
and long term evolution (LTE).
Moreover, the introduction of digital TV replaces the traditional analog TV and
integrates many other services together in to one box. Ubiquitous nature guarantees
the services are available anywhere at any time regardless of the access technology or
the access terminal. Compared to other service architectures ubiquitous architecture
has its own model for multimedia services where services are provisioned in order to
realize a business model interconnected with software and hardware. In terms of pro-
viding pleasant multimedia service over ubiquitous network require proper monitoring
to assure all functional models and elements performs properly and enables reachability
to different domains of the network.
2.3.1 Service Continuity
Provisioning mobile multimedia content is still a challenging issue in intergraded service
environment due to the requirements in quality assurance, latency, jitter and packet
loss. Providing uninterrupted smooth flow of transmission require more sophisticated
technologies and more investment on implementation. The Fig. 2.3 shows example
scenario for service continuity.
Figure 2.3: Seamless service continuity in user-driven ubiquitous networking environ-
ment guarantees service access irrespective of user context
Avoiding interruption in mobile environment tackles with proactive decision mak-
ing about user context. Moreover, the devices equipped with multiple access technolo-
gies improves accessibility and guarantees smooth delivery of content. Development
of cost effective electronic devices in communication poses individuals to use more
hand-held devices connected to each other in their day-to-day life. Further, service
continuity has become a crucial issue due to heterogeneous network elements in the
9

local networks. Specially, delivering multimedia contents over local networks or WWW
has become a demanded issue for content providers.
Broadcast or the cable television is another form of competitive technique used
by many service provides to deliver real time content to subscribers. However, ser-
vice integration over IPTV made it more popular among many other technologies.
IPTV provides guaranteed delivery over the local network to the customer premises,
at least one video stream together with an audio stream. In IPTV service environ-
ment service provider fix the performance metrics. In order to manage the quality of
service, content providers develop video quality metrics (VQM) where all performance
measures merged together and assigned to a common scale (Kerpez et al., 2006). Au-
thentications, authorization, accounting (AAA), capacity planning, error correction
and subscriber management are some of the important aspects in multimedia service
assurance.
Unlike in many other traditional streaming technologies IPTV uses different au-
thentication, authorization mechanisms to reduce the latency. In commercial perspec-
tive subscriber management is an important task in service management. Normally,
they provide bulk of services as a package with few value added services. Subscribers
can choose the preferred packages on their interest. Generally, IPTV service provides
use security measures for authentication, authorization and accounting. Video on de-
mand (VoD) is another value added service over IPTV. Even though, generated traffic
is smaller comparable to IPTV traffic, multiple simultaneous VoD traffic flow over same
channel can increase the load considerably. The content protection is achieved with
digital right management (DRM) which performs similar to AAA (Kerpez et al., 2006).
And it manages the subscribers in terms of controlling access to authorized media con-
tents. Bandwidth and delay are the key factors which affect the content delivery in
IPTV environment and it hardly affect the quality of service.
Moreover, the development in broadband technologies facilitate access IPTV over
mobile devices like PDA, mobile phones over the technologies like enhanced data
rates for GSM evolution (EDGE), 3G, hi-speed downlink packet access (HSPDA) and
WiMax. NGN platform is developed to meet the requirement of IP base environment
facilitating different media contents like audio, video, text, graphics and data over
the network. Continuity feature in NGN enables service providers to deliver content
without any significant change to the existing infrastructure. The immense IP sup-
port in NGN enables exploding many services easily over NGN while ensuring service
continuity over the network.
2.3.2 Context Awareness in Multimedia Applications
Widespread mobile technology and portable devices tremendously increase the devel-
opment and usage of context aware applications in hand-held devices (Wang, 2004).
Once user context (see Fig. 2.4) is clearly determined by the system or the applica-
tion, it will select the best fit content, end terminal and an appropriate media codec
from available resources with subscribers. When a subscriber initially makes a request,
context aware application grab the context information received with service request.
And that information is used to select the best content. Particularly, this information
is provided by the context provider.
Further, it temporarily stores this information in a context server for further usage
10

Figure 2.4: Context aware applications are responsible for self determination of com-
munication technique and the suitable terminal with proper media format
and codec
in decision making. This context information results execution of automated commands
or fetching some specific information with respect to user context. Evolutionary de-
velopment of all-IP networks connects various devices together over local network and
Internet. This ensures the seamless accessibility. Context awareness fundamentally
believes three basic steps like context capturing, context analysis and content delivery.
In a business model network provider gathers user context and update the context
provider enabling delivery of appropriate content to context user (Docter et al., 2007),
selecting terminal device, choosing among codec and adaptation technology. Respon-
sibility of context provider always lay on delivering right context at the right time
to the content provider. Context aware applications or services always interpret the
received context information and process data to choose among the correct contents.
Context aware service providers are capable of delivering the best fit content according
to received context information. This intelligence is realized by training the systems
and analyzing different context information.
In (Wei and Chan, 2010) propose a scheme for context reasoning based on ontology.
They have developed a layered architecture which promotes a hierarchical design, with
each layer assigned a well-defined role. This architecture is divided as program layer,
decision layer and knowledge layer. In program layer there are two main functions
services and tasks. Further, it divides the context knowledge in to three components
as; service ontology, context ontology and Tasklet ontology.
• Context ontologies model: This module various the context entities to share the
contextual information in a dynamic service environment.
• Tasklet ontologies; This describes the properties of tasklets and the requirements
for conditions.
• Service ontologies; This describes context-aware service properties the require-
ments for tasklets.
11

Figure 2.5: Ontology based context reasoning scheme (Wei and Chan, 2010)
But this implementation involves many functional modules while increasing the com-
plexity of the application.
Pervasive systems are effort of in-cooperating devices to build up common com-
puting paradigm to establish context aware system in day today human life (Zaslavsky,
2004). Pervasive systems monitor the user context and react according to the intel-
ligent. Basically, the applications discover the context and adapt accordingly to fit
the existing environment. Even though, it is invisible from our day-to-day life ubiqui-
tous computing fulfill many human needs and wants embedded in our daily life style.
Nano-technology and tremendous improvement in wireless communication assure hu-
man activities somehow related with computers and software which are carefully tuned
to offer automated human assistance. This nature facilitates context aware applica-
tions to perform better in existing communication environment. Specially, context
aware mobile applications provide a good artifact for self support context awareness.
If a person is traveling on a train or a bus, his mobile can suggest him to listen some mu-
sic, watching video or do on-line shopping until he reach his destination. This provides
a good example for self support applications. Basically, any context aware application
gathers context information from the sensors round it and process accordingly to serve
the best quality of experience (Menai et al., 2009). With the improvement of context
awareness attached to devices, many applications or services was developed to retrieve
the context information and dynamically change application nature to deliver the best
user experience. The contextual information received by infrastructure is forwarded to
the application and appropriate action is taken by the single or multiple devices using
the application.
RFID is a leading technique of gathering context information. Especially, they are
used in detection of location information. RFID enabled mobile supports auto config-
uration appropriately to the context. For an example, if you enter in to a shopping
mole your PDA will suggest you items to purchase while you walk through different
12

sections. If you enter in to a class room or cinema theater, your mobile will automati-
cally configure in to silent mode or reduce the level of ringing volume. RFID provides
good tracking mechanism providing location base information to context aware appli-
cations. The context aware middle-ware infrastructure transforms the physical space
to computational model. This middle-ware facilitates gathering environmental condi-
tions and transforming them in to context information. Basically, it operates as a data
acquisition mechanism like in sensor networks. Mobile learning is another interesting
context aware application. And it senses the mobile environment and adapts content
favorable to user context. Dynamic change in environment exploits the challenge in
developing systems which can be trained for learning sequences obtained in different
user context.
Heterogeneity of the network introduces another challenge in accessing context
service. However, in service providers perspective they are responsible for providing
service for all heterogeneous devices in the network. Context awareness requests change
in the context to dynamically adapt the content. This is the challenging issue in future
context aware applications.
2.3.3 Content Delivery in Ubiquitous Environment
Improvement in wireless communication integrates many value added services into
hand-held mobile devices. This came more popular among mobile subscribers due to
the concept of Content following user. Mobile TV is such a service where the television
content could be carried with the subscriber. Actually, we are in the evolving age
of mobile TV. But providing non disrupted continuous video stream is a challenging
issue in mobile environment. Mobile TV service allows seamless service accessibility in
mobile range while providing continuous streaming over the wireless medium. Deliv-
ering traditional TV media content to mobile devices clams reproduction of content in
to compatible formats and delivering over noisy channel. This clams error detection
and correction mechanisms in customer side. Still it is tolerable since dropping few
packets does not harm the experience severely. In mobile TV transmission they use
digital video broadcasting hand-held (DVB-H) or 3G scheme. Newly developed IP
based video transmission (see Fig. 2.6) provides more advance video streaming over
fixed line for delivering contents. The service integration among VoD, IPTV and In-
ternet browsing together in a single package makes subscribers to interchange among
services over a single access session. Basically this technology introduce personalize
television concept.
So, the subscribers will get the access to common media content over live broadcast
television but at the same time they will have the access to control the content in their
preference. IPTV provide immense control over the contents to subscribers. Apart
from standard definition high definition television came in to the arena due to higher
expectation of digital subscribers. But, this introduces a trade-off between video quality
and the bandwidth. Standard Definition television (SDTV) uses 1-4Mbps while high
definition television ranges from 4-13Mbps.
This restricts the maximum number of HD channels to 10-20 due to high band-
width consumption. Since, quality video streaming is highly affected by the packet
loss or delayed transmission. Quality assurance is a quite important phenomenon in
IPTV or VoD environment. Due to limited bandwidth and the geographical disper-
13

Figure 2.6: IPTV content delivery in ad-hoc service environment providing platform
independent service environment
sion of subscribers delivering content under acceptable quality measures is a critical
problem for operators. So, that they came up with a new architecture where content
is geographically spread to increase the accessibility to overcome this issue.
CCDN concept is becoming more popular since it is very well supported in IPTV
and many other real-time services. CDN consist of three basic operation models like
CDN controller, cluster controller and content delivery or the media servers (Menai
et al., 2009). CDN controller manages the client requests initiate the user session.
Further, it can identify the user localization, network load and redirect the request
to closest or the desirable cluster controller or another CDN controller. Basically,
cluster controller is responsible for handling or redirecting user request media servers
in the same geographical areas. This mechanism distributes the network load among
geographical clusters. The content storage is known as content delivery function (CDF).
Basically, this architecture proves that load balancing could be easily achieved in IPTV
environment. Generally, we consider the live media content delivery to be broadcast
type of transmission. Later it was narrow down to unicast transmission where only the
requested user is provided the media content. This dramatically reduces the network
traffic in the mobile and IPTV environment. Especially, with mobile TV environment
this is more significant.
2.3.4 Cross-Layer Adaptation for Multimedia Applications
Content adaptation is a complicated process which consumes more systems resources
like processing power and memory. So that, there should be a better interaction be-
tween different operational layers which utilize the resources over this process. This
implies the requirement for cross layer adaptation as shown in Fig. 2.7. Designers are
more concern in resource optimization while cross layer designing. However, this is still
an unsolved problem among the researches since no solution could optimize resources
14

Figure 2.7: Multimedia adaptation middle-ware platform which controls the media
characteristics to format the content to fit the end user requirements
in different layers at the same time. So, they suggest iterative optimization or decision
tree approach to solve this problem (Schaar and Shankar, 2005). Basically, the solu-
tion suggests optimizing few strategies but not all. This involves grouping strategies,
identifying parameters, layers or sub layers to be optimized. Real-time streaming over
wireless network is a challenging task. Since, channel properties could be changed over
the localization, time or the environmental conditions. Traditional stream expect to
have long buffers for error correction and adjusting channel parameter. In other words,
long buffers perform poorly in video transmission. Since, it can introduce more delay
over the channel. The nature of transmission over wireless media is not similar to wired
transmission. This requests for separate protocol architectures like modified automatic
repeat request (ARQ) and error correction.
Robustness of video implies the fact that transmission can be managed to adjust
such immediate drop in quality. Scalability of multimedia content refers to the number
of users simultaneously access the media. Due to the evolvement in Internet the basic
needs for services immensely changed. It results to reduce the complexity of accessing
services and same time brings down the cost of subscribing to new services. Still it is a
good technique in exploding many services where quality of service (QoS) is not a hard
concern. We find the most critical issue in network scalability as heterogeneity. Due to
heterogeneous devices connected to the network, scaling the media content to fit device
properties is a challenging task. Because, this implies the requirement of exchanging
scaling parameters, selecting best coding model, transfer rate and tolerating channel
noise makes this to be a complex process.
Transcoding is a technique used in reducing object size in the content to be de-
livered. The process of transcoding systems are divided in to three classes as client
based, server based and proxy based. But, client base transcoding is found to be dif-
ficult due to the low bandwidth and client processing power. In server based model
suggest centralized approach where server do the scaling and transmit to the client.
But, this introduces a problem in understand the client requirement for transcoding.
This results transcoding process assigned in to the proxy. Proxy has two options like
15

merely transcoding the input media or consider user context in transcoding process
(Hsiao et al., 2008). Even though, this process lowers the media quality still it could
be presented in a satisfactable level. Further, it is noticed that multimedia content
management is another important concern in content or the service providers perspec-
tive. It is more complicated to deal with media contents of different size and formats.
And at the same time it requires large capacity to store the content. Not only that they
find this complexity in service provisioning and billing (Bellinzona and Vitali, 2008).
The work proposed in (Elias et al., 2007) suggests a proxy based framework for
content adaptation. This approach relies on building up an efficient tree with selected
set of services optimizing resources. This acyclic graph or the tree is constructed
considering client, end terminal, multimedia content and the network profile. Content
adaptation is generally classified in to two classes as dynamic adaptation and static
adaptation (Elias et al., 2007). Rather than accessing already created content (static)
by the provider, dynamic adaptation gathers information like network, client, and
devices to recreate the content accordingly. Proxy based adaptation involves entering
a third party entity making decisions between the content servers and clients. The
suggested framework deals with matching destination profile and the source profiles.
Client proxy integrate the client profile with the device properties extracted from
the client request and merge it to the source profile in order to decide the best adap-
tation model. Different video coding standards like moving picture experts group
(MPEG)-2, Video/H-261, H-263 and MPEG-4 provides scalable options to certain
extend (Aggoun et al., 2008). Content providers perspective DRM or the content
protection is another important security concern in media delivery. This implies the
requirement of DRM in multimedia delivery. The growing technology in high speed
transmission over Internet provides increased media experience for customer. And at
the same time it introduce a new era in personalized high quality media services.
In multimedia communication cross layer design has become a good research area
since media content delivery for triple play devices is a hot topic among the researchers.
Service convergence is another important aspect in content adaptation. Scalability of
media content allows heterogeneous devices to connect to the network regardless of
its localization. This raises the requirement for cross layer adaptation to suit the
context of use. There are many cross layer adaptation mechanisms which allows adapt
the service environment to user context. Even though, terminals like mobile phones,
PDA are capable of receiving media content at anytime from anywhere the problem of
adapting the content is still an unsolved problem.
The challenge of meeting the terminal capabilities, delivery constrains and man-
aging quality of service is a quite complicated process in multimedia services. This
implies the requirement of maximizing the cross-layer utility to improve the QoE. This
raises the problem of What is the context of use and what the best adaptation model?
But the answer for this question entirely depends on the information received from
the end terminal. There are many cross model adaptation techniques being suggested.
The model suggested in (Prangl et al., 2006) introduces decision making process con-
sidering user context, terminal capabilities and resource limitation on server, network
and client side. This work suggests four basic processes in adaptation like parameter
mapping, utility model configuration (UM), adaptation decision taking engine (ADTE)
and adaptation engine (AE).
Further, it implements and observes the audio/video stream variation to maximize
16

user experience under given resource constrains. And they suggest four algorithms find-
ing optimal audio/video variation in cross model multimedia adaptation (Prangl et al.,
2006). The latter improvements proposed with distributed contents reducing the delay
in accessing the media. Normally, such applications are applicable for commercial,
health care, emergency and tourism. Such systems we name as pervasive systems
where multimedia content is distributed and content is adapted on user preference,
device properties and network capabilities (Berhe et al., 2005). M-learning is another
fast moving research area where learning process is done over the hand-held or fixed
devices. This technology lay down the basic content accessibility making intelligent de-
cisions over the accessible devices. The complexity in M-learning comes when adapting
the media content and selecting the proper device to receive.
For an example, assume a scenario where a person is watching a movie on his
way back to home over his mobile phone. Once he reaches to home, he necessarily
does not have to use the same device. But now the content is delivered to a High
Definition-TV at home with improved audio/video impacts. In that sense, scaling the
media content is an important concern in content delivery. Scalable video coding (SVC)
provides solutions to overcome this problem. SVC supports the backward compatibil-
ity for traditional media contents like video, speech while assuring network/terminal
compatibility (Hewage et al., 2007).
2.4 Mobile IPTV Service in Ubiquitous Networking Environment
In Fig. 2.8, we see an example scenario in the home environment. Bob is watching a
movie in the TV set at home. When he requests the movie, the service platform we
defined here automatically detects all possible rendering devices around access radius.
For an example, context-aware system will recognize different types of devices such as
the high-definition television, mobile phone and PDA. Then it will decide which device
Figure 2.8: Service scenario in home environment for seamless service accessibility over
different end user terminals
to deliver different media contents like visual, audio affects and subtitles. For an
17

example, the visuals are delivered to high definition television while audio is delivered
to hi-fi setup and subtitles to his PDA. Further, he will gain total control over video
presentation over his mobile phone. Meantime, his friend comes to see him and both of
them watch the movie together. Ultimately, Bob is getting a call from his wife to pick up
her from the supermarket. But Bob is so interesting watching the movie. So, he decides
to takes the session with his PDA. We term this capability as The content following
user. His PDA is having an inbuilt content guide implemented using open source -
synchronized multimedia integration language (SMIL) player. Likewise, he can get
tremendous control over video presentation while moving outside the room. Moreover,
the same video might play in wide screen in his room. The above example presents
service continuity and service integration of ubiquitous computing environment.
In service providers perspective, there are many undergoing processes for deliv-
ering quality content to their subscribers. First, incoming user is authenticated and
authorized. Attached to the example scenario, Bob request the same content over his
PDA, service provider let him download the stream and automatically start from the
place he stopped. Then, service will find the best rendering technology which minimize
the noise and interferences. Basically, this platform provides dynamic content delivery
and rendering over the selected content in a user friendly manner while adapting to
the user context.
2.5 Threats Over Context Collectors
2.5.1 Limited Resource Constrain of Sensors
Context aware services use sensors in order to capture context information. With
the improvement of micro-controllers and wireless communication technologies sensor
networks plays a big role day today human applications. Though, it is originally
introduced for military purposes, now it is being used for many industrial applications
like environmental information gathering, health care, home automation, traffic control,
navigation and many other civilian applications.
Gathering context information is a challenging issue in adaptive service environ-
ment. The incorrect and erroneous information can mislead the applications and de-
grade the user satisfaction. Therefore, gathering necessary information in trustful
manner helps to provide a quality service. Normally, sensors are used for gathering
context information. But, sensors can be compromised or mislead easily to produce in-
correct data or disturb the communication among them. This implies the requirement
for a secured channel and a protected environment which guarantees an uninterrupted
communication.
Any sensor is equipped with micro controller with limited computational capacity
battery power and a radio transceiver. Always the battery life time is a critical factor
in most of sensor networks since they need the remote operation. Sensing nodes are
made to be cheaper with the use of latest technology helping large deployment and
gathering more precise data. We can find the sensor network applications operating on
different areas like tracking, monitoring and controlling. Special applications for WSNs
include habitat monitoring, object tracking, nuclear reactor control, fire detection, and
traffic monitoring. There are many application of WSNs used in detection of natural
disasters, sensor nodes can sense and detect the environment to forecast disasters before
18

they occur.
In biomedical applications, surgical implants of sensors can help monitor a patients
health. For seismic sensing, ad hoc deployment of sensors along the volcanic area can
detect the development of earthquakes and eruptions. WSNs are deployed over a
region where some phenomenon is to be monitored. Specially, in battle fields these
nodes are deployed to detect enemies movement to track their activities by detecting
the desired parameters (heat, pressure, sound, light, electro-magnetic field, vibration,
etc). These information need to report to the base station, which analyze the data and
make decisions over the received information. Unlike any other traditional wireless
networks, WSN has specific design and resource constrains. Resource constraints in
sensor network includes limited amount of energy, short communication range, low
bandwidth, and limited processing and storage capacity in nodes. This feature enables
WSNs are more prone to attacks and threats. Basically, sensors could be divided in to
two as generic sensor nodes and gateway sensor nodes.
Generic sensors are equipped with sensing elements which are capable of measuring
physical environmental factors like light, temperature, humidity, barometric pressure,
velocity, acceleration, acoustics, magnetic field, etc. The task of gateway nodes is
to gather data from generic sensors and relay them to the base station. Gate-way
nodes have higher processing capability than generic nodes. Basic sensor network
model generally assumed to be static. However, some recent applications of sensor-
nets make use of mobile sensor nodes, which poses some unique challenges to sensor-net
systems researchers. Some applications like detecting land mine in battle field needs
remote operation their own. Mobile sensor networks are used where remote operation
is required for gathering information. Mobile sensor network have distributed nodes
around the target area, each of which has sensing, processing, communication and
locomotion capabilities.
Sensor nodes have very limited storage capacity and Memory. Due to the restric-
tion in code space the algorithms suppose to be more optimized in code space and
there functionality. Further coding supposes to minimize the storage for variables,
arrays and other resource consuming modules. The properties like capacity, power,
topology, mobility and routing of the wireless sensor networks have interdependent
characteristics (Karlof and Wangner, 2003). Especially in the security aspect develop-
ers are worried about resource utilization (power management, bandwidth utilization
and mobility management) and secured data transmission. Therefore it is important to
understand the relationships between different aspects of wireless sensor network op-
eration to guarantee secure communication among sensor nodes (Walters et al., 2007).
Normally, nodes are equipped with non rechargeable batteries where as some could
be charged after the usage. But batteries cannot replace easily due to higher operational
cost. Since battery charge decides the life time of the nodes it is necessary to control
the transmit power. In the implementation of protocols they are more concern about
the energy consumption. Sensor nodes are developed to operate under least power
consumption due to limitedness of source power. This restricts the radio range of the
nodes.
19

2.5.2 Communication Unavailability
This implies the condition where data get lost due to channel problems like channel
noise or network congestions. This results data loss, damaged packets or incomplete
data transfer among the nodes. A channel error in communication medium implies the
necessity of error correction mechanisms in sensor networks. This could result failures
in data transmission in WSNs. If the lost data consist of some necessary information
like security keys, then the whole transmission will get corrupted (Du et al., 2004).
Even though the channel does not have any problem still communication could be
destructed by any other node who is trying to retransmit data. This happens due to
the broadcast nature of the wireless communication. When the node density is higher
there is a higher probability to get congested. Therefore in the designing stage it is
more important to consider the radio range and node density of the network (Tamer
et al., 2000).
2.5.3 Unattended Operation
Depending on the nature of the application attacks model differs. That could be
due to natural facts or due to human activities. When node exposed to the physical
environment it could harm with natural occasions like wind, rain or humidity. Else,
it could be physically damaged by human (adversary) with the interaction to disturb
the transmission. Therefore the deployment is expected to be in a secured location to
protect them from such physical attacks during the operation. In the case of remote
management of WSNs are more critical in military applications. In such cases, the
nodes need unattended or remote operation to capture reliable data. So that the node
itself expected to be organize and utilize the existing resources to operate in the best
performance level. Specially, in mobile sensor networks we allow nodes to move in the
target field in gathering data and transmitting them to the base station. This improves
viability of sensor network. Therefore the design of the sensor network more important
to achieve proper operation.
2.6 Security Concern of Sensors
Sensor networks share many commonalities with wireless networks. Therefore, we
can say that WSNs claims both unique and common requirements claimed by wireless
computer networks. Data confidentiality is another security issue in computer networks
as well as sensor networks. Confidentiality refers to the extent to which data could
be trusted. Depending on the nature of the application the level of confidentiality is
different.
To protect data from intruders the transmissions are encrypted with secure keys
(Chan et al., 2003). But, in this case all kind of keys and sensor identities need to
be encrypted since these data are very much sensitive in communication among the
nodes. To achieve data confidentiality encryption methodologies are use. Though, data
confidentiality is guaranteed in a network still we cannot ensure security since intruder
can hanged existing data. This means the data is still not protected. For example,
an intermediate intruder might modify or add some tracking data in to the normal
IP packet resulting a threat to the network. Then the packet is sent to the original
20

destination as usual. With data integrity we can ensure the data is not modiﬁed
or added during the transmission. Further, we must make sure freshness of data.
Older messages need to be dropped since they can stay in the network and reach the
destination being delay. So that, destination might think it is the most recent data
and act accordingly misleading the nodes. Therefore, the freshness of data needs to
guarantee in the network for secure communication.
2.7 Attacks on Wireless Sensor Networks
2.7.1 Attacks on Data Link Layer
Since, all sensor nodes in the network have same rights for accessing the communication
medium data link protocols has been more vulnerable to attacks. Any adversary got
rights to access network can access the channel randomly and transmit or eavesdrop.
This could be more serious, when nodes inject and alter data being transmitted. Such
attack models can be subdivide in to three categories as below (Xiao et al., 2005):
1. Data integration attack
2. Collision attack
3. Exhaustion attack
To pretend against these attacks link layer suppose to have three basic security con-
ditions. Those are presented in the IDS architecture proposed in (Xiao et al., 2005)
which consists of three basic modules in detection architecture:
1. Collision detection system
2. Power anomaly check
3. Data integration check
Nodes compute the rate of collision (per second), and the ratio of collision. Moreover,
nodes records waiting time after sending the RTS packets, packets stay in the queue
and the packet drop during the communication. In case of a collision, these parame-
ters will remarkably change. And the nodes will detect the presence of intrusion and
generate an alarm to notify others. The presence of power check module guarantees
long term battery usage while protecting system from adversaries those who try to
depreciate the battery life of reluctant nodes (Lazos et al., 2005). If the nodal power
depreciates rapidly, we can expect that an adversary is attempting to send some packets
repeatedly. The collusion detection module can detection of such behaviors immedi-
ately and generates an alarm. The module deﬁned for data integration keep checking
the messages to assure no adversary modify the message in between during the trans-
mission. If the data received not similar to the original data send by the legitimate
node detection module will generate an alarm (Xiao et al., 2005). In case of collisions
and power alarms, the communications is temporarily stopped and force the nodes to
move into sleep mode for a few seconds. This can mislead an advisory forcing to stop
communication with the reluctant node. In the presence of an integrity alarm, the
transmitting node will drop a message requesting the source node to retransmit sane
massage back to the generated node (Xiao et al., 2005). With the received message we
can make sure existence of data integration.
21

2.7.2 Attacks on Network Layer
Initially, the nodes suppose to organize themselves and when they receive HELLO
packets. So that, protocol assumes those nodes reside in the given radio range. Nodes
should be authenticated such that messages are not proofed or eavesdropped by an
adversary. Periodically, nodes suppose to store the neighbor information in the memory
then this information is sent to the base station frequently. So, the network topology
could be easily mapped at the base station. Since, nodal power depreciates with the
communication turns nodes get vanish sometime after deployment. Moreover, the
mobility of the nodes results to timely change the network topology demanding to
monitor the nodes continuously. Therefore, the topology derived at the base station
will valid only for a given instant. When the sensor node is activated the detection
module must automatically start to detect any intrusion in the network. Whenever,
the module detects the existence of an attack the countermeasures are taken. These
countermeasures could be defined as,
1. Checking artificial links
2. Checking neighborhood information
There are many routing protocols used by existing sensor networks (Marti et al., 2000).
These protocols could be fit in to different categories as shown below (Sattar, 2004):
1. Flooding - SPIN (SPIN-1 and SPIN-2)
2. Gradient - Directed Diffusion, GRAB, GEAR
3. Clustering - LEACH, TTDD, GEAR, GAF
4. Geographic - GPSR, GAF GEAR
The routing protocols used in sensors networks developed with least complexity due
the low processing power and less capacity. So, developers pay more attention on
simplicity of the protocols with effective routing. Because of this, sensor nodes are
more susceptible to different form of attacks (Ngai et al., 2006). Almost all routing
protocols fail at least against single attack model shown below.
1. Selective forwarding
2. HELLO flood attack
3. Sinkhole attack
4. Sybil attack
5. Wormhole attack
6. Acknowledgment spooling
7. Altered replayed or spoofed routing information
22

Malicious nodes might simply drop the packets that are forwarded in the network.
In selective forward attack malicious node refuses to forward the received message.
Simply it forms black hole for certain source packets or to the whole incoming packets.
We can believe that a malicious node intended in selective forwarding might follow
the path with least disturbance. Many existing protocols in sensor networks require
HELLO packets to advertise themselves and to get to know the presence of other nodes.
HELLO flood can be formed by advertising a very high quality route to neighbors.
This will force other nodes in network to choose the same path (Hamid et al., 2006).
A wireless sensor network consists of autonomous devices which keeps track on their
neighbors and exchange information in between. And the captured information is
transferred to a sink node or base station for decision making process (Lazos et al.,
2005). Many-to-one communication model is a highly vulnerable to sinkhole attack.
Flooding unfaithful routing information intruder easily execute attacks on neighboring
nodes. This form of attack could be more risky since whole communication system
could be misled.
Node impersonation and resource depletion attacks are two types of attack mod-
els which can disrupt both sensor and ah-hoc networks. Node impersonation means to
establish as legitimate node in the network by using an identity of some other node. So
that it can operate as normal node in the network and extract all necessary informa-
tion in the network. Resource depletion attacks more focused on consuming network
resources such that it will disrupt the normal operation (Sang et al., 2006). For an
example, an attacker might create large volume of data to a single node. It will result
to occupy all resources alone the path unusable for other nodes. This will rapidly waste
the battery and reduces the life time of the nodes.
Being exposed to external environment and mobility in nodes makes WSNs more
vulnerable to attacks. Through, it is difficult to protect against physical attacks, there
are many other techniques to protect against technical attacks. In the other hand,
prevention based techniques like data encryption and authentication consumes more
resources compared to detection based techniques. (Eschenauer and Gligor, 2002)
presents key management scheme which satisfy both operational and security require-
ments of WSNs. Since they need cryptographic protection in information exchange
key management protocols performs quite important job. But, it is a challenging is-
sue that WSNs still use traditional key exchange and distribution techniques where
trusted third party involves in communication. (Pavel and Trossen, 2006) introduce
novel detection based security scheme for WSNs assuming stable neighborhood infor-
mation. It allows detecting network anomalies and transceiver behaviors considering
signal strength and data rate. Initially, malicious node tries to establish as a legitimate
node in the network before it becomes a threat to network security. Sensor nodes are
made to be capable of isolating such intruders with dynamic statistical models which
detects anomalies.
Time synchronization is an important concern for any wireless network in hostile
environment. But, most of the existing time synchronization techniques are not de-
signed with security concern. This makes the WSNs more vulnerable to attacks. (Song
et al., 2005) presents a novel time synchronization scheme which resist to delay attack
where malicious attackers intentionally delay the transmission of time synchronization
frame with the intension to magnify the synchronization offset which makes attacker
get in easily. Topology of sensor networks change frequently with time and the broad-
23

cast nature of communication allow malicious nodes to enter the network with less
effort. Therefore, it is important to block such nodes entering to network before they
compromise legitimate nodes.(Kerpez et al., 2006) propose scheme for tracking multiple
co-dependently maneuvering targets using radio frequency identifiers (RFIDs). Appar-
ently, using RFIDs is a common technique since it involves less cost compared to other
location based services. Generally, intrusion detection schemes can be categorized in
to three as stand-alone, distributed, cooperative and hierarchical (Wang, 2004). Our
proposal carries attributes of both hierarchical and distributed architectures.
2.7.3 Log-distance Path Loss Model
Most of the actual propagation models could be simulated using analytical or empirical
models. Empirical approach involves recreation of observed data with derived equations
or curves. For the calculation of the link budget, empirical method uses all known
and unknown parameters resulting to reliable evaluation. There are some classical
models developed to predict large scale mobile communication system designing with
mathematical models.
By observing both theoretical and practical parameters, it was found that the
received power decreases logarithmically with the distance both indoor and outdoor
environments. Below we present the power depreciation with the transmitter receiver
separation (Onat and Miri, 2005).
Pd
pathloss ∝ (d/d0)n
, (2.1)
Ppathloss[dB] = Pd0
pathloss + 10nlog(d/d0), (2.2)
where d is the transmitter receiver separation, d0 is the close-in reference distance
and n is the path loss component. This implies the fact that path loss is logarithmically
proportional to the transmitter receiver separation. In this model, path loss exponent
depends on the propagation environment. Normally, in urban areas it is assumed to
be 2.7 - 3.5. And it is found that the path loss at a given point is random and log
normally distributed. So, we modify the equation adding Gaussian random variable
Xσ with standard variation σ. Therefore, we modify (2.2) as (2.3).
Ptot
pathloss = Pd0
pathloss + 10nlog(
d + speed
d0
) + Xσ (2.3)
This is known as log-normal shadowing. Basically, this implies the fact that signal
level at a defined location has Gaussian distribution.
2.8 Mobility Models for Sensor Nodes
In a mobile environment nodes move gathering and exchanging information. Therefore,
the distance between nodes always changes with time. We use Random-Waypoint
and Gauss-Markov mobility model for the evaluation of proposed architecture. In our
study we propose a intrusion detection architecture where nodes forward information to
base stations. Base stations are responsible for the detection architecture and making
decisions. Nodes dynamically connect with the base stations according to the received
24

signal strength. There are instances where one node is connected to more than single
cluster head. Specially, the instances like handover.
We organize whole network in to three hierarchical layers as sensor nodes, cluster
heads and base stations. And they are assigned distinct responsibilities. Sensor nodes
always gather information and forward to cluster heads where cluster heads analyze and
exchange information among peers in the same hierarchy. Moreover, cluster heads run
the detection algorithm for power and rate anomaly detection. BS gathers information
from cluster heads and stores them for future reference. In the manufacturing itself
cluster heads are developed with more capacity and processing power.
When nodes move, they experience different channel conditions and more impor-
tantly they adjust the transmit power level to maintain expected signal to noise ratio
depending on the channel condition. In the defined model transmission is assumed to
be connectionless while routing decision is taken based on packet based. Moreover,
sensor nodes have isotropic antennas and they are aware of the locations. We assume
nodes are randomly deployed and mobility is modeled with both Random-Waypoint
and Gauss-Markov model. Firstly, we observe the detection probability for different
transmission power levels. We simulate the Random-Waypoint with (Camp et al.,
2002),
xnew = xold ± speed (2.4)
ynew = yold ± speed (2.5)
In Random-Waypoint mobility model nodes move randomly without any restriction.
In other words, nodes have no memory. The direction and speed is randomly cho-
sen independent of the movement of neighboring nodes. Such mobility models are
commonly used to simulate mobility patterns of mobile ad-hoc and sensor networks.
Random-Waypoint is firstly proposed by (Zhang et al., 2000). Then it became a
common benchmark for evaluating routing scheme in ad-hoc and sensor networks.
Gauss-Markov mobility constrained with laws of acceleration, velocity and the change
of direction. It implies the fact that current velocity and the direction depends on the
previous parameters. Thus Gauss-Markov model believes nodes have temporal depen-
dency of velocity and direction. This model was firstly introduced by (Mehedi et al.,
2008), where velocity and the direction is timely corrected. We present the stochastic
process Gauss-Markov with following equations (Camp et al., 2002).
Vt = αVt−1 + (1 − α)Vmean + σ
√
1 − α2 Wt−1 (2.6)
θt = αθt−1 + (1 − α)θmean + σ 1 − β2 Wt−1 (2.7)
xnew = xold ± Vt cos θ (2.8)
ynew = yold ± Vt sin θ (2.9)
The degree of dependency in this model is determined by the parameter α and β
which express the randomness or the level of memory. This model becomes memory
less when both α and β equivalent to 0. Wt−1 is a random Gaussian process with
0 mean and σ standard deviation. When nodes move out from the boundary the
mobility model manage to hold them within the target area. This is done via changing
the angular velocity by 1800
degrees.
When α and β equivalent to 1, Gauss-Markov model have the strongest memory
or the least randomness while illuminating some terms from the equations.
25

0 100 200 300 400 500 600 700 800 900 1000
0
100
200
300
400
500
600
700
800
900
1000
X − Coordinate
Y−Coordinate
Figure 2.9: Mobility pattern of a sensor node when routing is simulated with Ran-
dom-Waypoint model
0 100 200 300 400 500 600 700 800 900
100
200
300
400
500
600
700
800
900
X − Coordinate
Y−Coordinate
Figure 2.10: Mobility pattern of a sensor node when routing is simulated with Gauss
Markov model
26

CHAPTER 3
CONTEXT REASONING IN CONTEXT AWARE MULTIMEDIA
SERVICES
3.1 Introduction
In this chapter, a context reasoning scheme is introduced for home environment based
on the AHP. This model is capable of handling multiple objectives and sub-criteria si-
multaneously. Further, user-driven ubiquitous networking environment provides seam-
less integration of services and content from different local/global resources (Loke,
2006). Moreover, media adaptation is a major consideration when same content is
delivered to multiple devices simultaneously (Pavel and Trossen, 2006).
In addition, a use case is provided for seamless IPTV services in home environ-
ment and AHP is introduced in context reasoning. The proposed scheme for context
reasoning over the hierarchical context information tree provides service adaptation
by early identification of the user context. This scheme could be used to interpret
and enhance explicit user inputs to deliver accurate and precise predictions based on
gathered information. The modern context reasoning considers emotions and feelings
to produce more user friendly decisions (Pavel and Trossen, 2006). The process of
evaluating the context information is known as the context reasoning (Zahedi, 1986).
In (Pawar et al., 2008), a scheme of vertical handover is proposed which supports for
the multi-homed nomadic mobile service. Hence, it is found to be one of the most
challenging and important issues in future communication systems (Loke, 2006).
AHP based context reasoning is found to be comparatively easy and cheaper com-
pared to ontology based context reasoning schemes (Gu et al., 2004; Wei and Chan,
2010).
In this chapter technical challenges are discussed in the section 3.2 for context
reasoning. The usage of AHP in context reasoning is presented in the section 3.3. The
section 3.4 discusses the proposed model for context reasoning. Finally, the section 3.5
presents the conclusion.
3.2 Technical challenges in Context Reasoning
Context awareness provides good back-end support over existing IPTV service. It
makes the services more user-friendly and flexible. Here we focus IPTV services in
home environment which is subjected to frequent change in context. In addition to
that, context aware IPTV service in home environment is supported by the location,
time, device capabilities, network characteristics, etc.
Location-based information can be classified into two categories as indoor and
outdoor. Indoor environment is an extension to the smart home concept. In such en-
vironment, context information is forwarded to the local context manager at home
network or distributed context managers in the operator network. Moreover, the local
context manager is not always smart enough to take crucial decisions relate to flow
control like; quality of service management, minimizing delay and utilization of re-
source. Strategically, the network operators locate global context managers closed to
27

access networks to minimize the response time.
The concept of smart home provides a good support over context aware services in
the indoor environment. In home environment, context information is gathered with
the sensors which are capable of detecting voice, motion and environmental factors
like temperature, humidity and brightness. RFID is another common technique use
to capture the context information due to compactness and low manufacturing cost.
In addition to that, time shift TV is one step ahead IPTV which supports trick mode
operations like forward, backward, pause and play functionalities over broadcast TV.
In other words, time shift TV service offers subscriber freedom in time domain by
facilitating them to watch preferable media content which is already broadcasted over
linear TV. Basically, this service allows users to customize the normal broadcast TV
service according to their preferences.
For example assume a person who is watching normal broadcast TV in his living
room wants to go to the dining room and continue to watch the same content from the
place he stopped over another device. The Fig. 3.1 shows several supported devices
in the home environment related to context awareness. The concept of doublecast-
Figure 3.1: User context management in ubiquitous home environment which support
seamless service availability. This figure shows the existence of different
devices inside home and how they are connected to home gateway or the
set-top-box for content divergence
ing, introduced in (Balasubramaniam and Indulska, 2004), proposes solution for real
time seamless service continuity. In this scenario the service continuity is preserved
by delivering the same content over two channels simultaneously during the time of
handover. In the other hand, there are instances where same content is received over
several channels. Thus, during the time of handover devices have to synchronize the
streams. Handover is defined in two generic ways; device to device with or without
28

a location change and location to location with or without a change in device. In
a heterogeneous networking environment, different devices have different capabilities
in processing, storing, codec supportability and so on. Hence, in context aware ser-
vice environment, local context manager identifies all supported devices in the target
environment and exchanges information with them.
When handover takes place in a home environment from one device to another,
local context manager at home sends necessary information to the remote server to
adapt media content in terms of format, resolution, volume level, etc. In the above
discussed scenario, the local context manager is responsible for making the local deci-
sions like handover within home environment. When, user comes out from the home
environment context information is hand-over to the context managers in operator
network.
In multimedia services proper utilization of the network resources and managing
of QoS parameters are very much important. Hence, compared to broadcast traffic,
unicast traffic consumes more resources in a network. Unicast traffic can significantly
increase the network utilization since each subscriber consumes individual stream from
content server or proxy server. Thus time shift TV and VoD brings more weight in to
the network than liner TV since users are served with dedicated streams as presented
in Fig. 3.2. Meantime, proxy servers are used to reduce the traffic load in the core
network with buffering the contents requested by the subscribers.
Figure 3.2: Unicast and multicast traffic in IPTV services. Liner TV stream always
broadcast reserving fixed bandwidth for each channel. On the contrary,
VoD and time shift TV assign an individual stream for each connected
user
Delivery of an uninterrupted stream requires good understanding of the communi-
cation channel and proper error correction mechanisms (Menai et al., 2009). Internet
Engineering Task Force (IETF) has developed a protocol suite to support content deliv-
ery in multimedia service environment. Further, the standards defined by audio-video
transport working group of IETF has two protocols as real time protocol (RTP) and
real time control protocol (RTCP) for content delivery in real time service environment.
In an actual implementation couple of functional models belongs to both network and
user device are defined (Pawar et al., 2008). In addition to communication tools, de-
signers are now endowing everyday objects with context-aware capabilities. Even, toys
are developed with inbuilt context aware systems. There are dolls which are capable
of recognizing events like hitting, touching, lifting etc. Further, they can emit music
or sounds according to the situation and the way it is handled.
29

3.3 Analytic Hierarchical Process in Context Reasoning
Compared to operator networks, home networks are small and provides limited func-
tionalities. Home network provides a good environment to experience context aware-
ness since it limits to a defined boundary. In a home environment, subscribers are
reluctant to frequent handover from device to device and location to location since
there is a greater possibility that user keeps moving here and there and changes the
devices being used by the time (Wang, 2004). Operators introduce sensors integrated to
devices for gathering context information like user context, environmental and system
conditions (Mehedi et al., 2008). Seamless service continuity demands proper handling
of gathered information and isolating useful information for context reasoning.
However, too much context information increases the complexity of context rea-
soner or decision support system since it involves more unnecessary computations and
analysis (Loke, 2006). The AHP breaks down decision support process into several
parts. Decision-making is achieved by developing a pair-wise comparison over all levels
in hierarchical context tree.
It deals with relative rating instead of absolute rating. Therefore the final re-
sults are more reliable and realistic compared to the results obtained with absolute
rating since proposed methodology does overall grading. The proposed scheme per-
forms better when there are several options available for the final decision to be made.
This nature of AHP propose a mathematical model upon which many problems can
be modeled in its own domain. AHP approach can be further used for predicting
likely outcomes, project planning and decision-making, group-wises decision-making,
resource allocation process, and cost/benefit comparisons (Randall et al., 2004). The
most important consideration with AHP is that, it forces prioritizing over different
factors which significantly affect the final decision. Further, it allows revisiting avail-
able information periodically to determine and recalculate for the dynamic changes in
criterion or intensities. In addition, at the same time, some factors could be ignored
in the process due to insufficient information or low weight on final decision.
We assume an example scenario where the subscriber is watching a normal broad-
cast TV (i.e., linear TV) in his/her bedroom. After some time he/she moves to another
room and starts watching the same content on another device from where he stopped.
In this scenario we can figure out some important events in operators point of view.
This involves service provisioning in operators perspective. Those subscribers have
more than one profile to access different applications. Initially he/she was a liner TV
subscriber but after some time, he/she becomes a time shift TV subscriber. This makes
things more complicated in operator side since it demands to handle complicated sub-
scriber profiles (Kerpez et al., 2006). In addition, service provider must make sure that
subscriber will not get disturbed when they switch to different user profiles.
Generally, context information is categorized into two, Static and Dynamic. Static
information is quite stable with devices or prefixed by the subscriber, operator or the
manufacture. On the other hand, dynamic information can change over time, location,
system condition, network traffic, etc. Moreover, the predictions on dynamic infor-
mation are difficult since it depends on many other external factors. And it demands
to study previous information sets to predict on the expected behavior or the results.
Herewith, we propose a new context reasoning scheme for handling contextual infor-
mation and decision-making system combined with AHP. The AHP is a multi-criteria
decision-making tool which derives the ratio scale from pair vise comparison. This
30

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