| - Publications
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My research interests include system architecture and security design; cross-layer network protocol design
and testbed experimentation; software-based prototyping for wireless and wireline networks and middleware solutions.
Main topics of interest
Access network architectures, planning and security protocols
Machine-to-Machine network and middleware system architectures and security solutions
Cloud network security
Smartphone application security
Secure mobile IP telephony
Intrusion detection
WiFi mesh, LAN and ad-hoc network design
UWB networking
Network systems, middleware and mobile device security
I am interested in diverse problems that are mainly related to wireless and wireline network architecture and
security, as well as
mobile device anti-malware design. I am particularly interested in middleware system architecture design and security,
and issues that involve
application layer security, intrusion detection,
secure cloud services, transport layer performance dependencies and secure interaction with WiFi networks.
Some of these directions involve
application development
as well as experimentation with commercial broadband networks.
Wireless access networks and testbeds
On wireless LANs and mesh networks, I am mostly interested in
measurement-based methodologies, as well as prototyping for assessing performance improvement and security
algorithms and protocols. I have designed deployed many wireless experimental networks across various research and corporate sites.
In particular, I have designed and deployed the
UCR Wireless Testbed,
an indoor 52-node testbed in the third floor of the Engineering
Building Unit II, at UC Riverside.
More than that, I designed and built the
Intel Research wireless testbed at the University of Cambridge, UK,
consisting of 80 nodes all deployed indoors across the 3 floors of the
William Gates building.
Finally, the
Orbit-based wireless testbed at the University of Thessaly, which has been
deployed both indoors and outdoors in the Electrical Engineering campus building.
Although I have participated in various implementation-based studies, I am mainly interested in
efficient network architectures, topologies and MAC/PHY protocols for mesh settings,
MIMO measurements, network coding, automated power control, channel allocation and load balancing algorithms for wireless LANs,
routing DoS attacks and anti-jamming techniques.
Ultra Wide Band networking
My research on UWB involves the design of methodologies that can be
adopted by UWB MAC protocols, in order to alleviate
the multipath delay spread effects. The UWB technology offers a promising
high capacity solution for wireless networks with short-range links. It supports high transmission rates and is
constrained to low-power operations. It can be deployed with low cost, it projects minimal interference
to existing wireless systems and is especially suitable for military
and disaster relief deployments.
Additional networking interests include directional/smart antennas,
secure location verification, vehicular networks and
efficient multimedia transmission over wireless environments.
In what follows, I provide brief descriptions about the projects that I have been involved with.
Work on wireless access networks and systems
Detecting Route Attraction Attacks in Wireless Networks
IEEE MASS 2011
Selecting high performance routes in wireless
networks requires the exchange of link quality information
among nodes. Adversaries can manipulate this functionality
by advertising fake qualities for links; by doing so, they can
attract routes and subsequently launch pernicious attacks.
Our measurements suggest that malicious route attraction can
fatally impact throughput. We design a framework that is
effective against both independent and colluding attackers. In
the latter case, we consider both local and remote colluders.
With local collusion, malicious nodes exchange and advertise
fake routing information to increase the probability of being
selected as relays. Remote collusion refers to nodes residing
in distant parts of the network that (i) create sybil identities
in a local neighborhood and / or (ii) utilize link quality
reports to advertise fake links. Our framework combines
packet signing and frequency hopping to accurately detect
the adversaries. We implement the framework on our testbed
and conduct experiments to assess its efficacy. We observe
that our framework provides significant throughput benefits
by detecting attackers with 90% accuracy.
Coping With Packet Replay Attacks in Wireless Networks
IEEE SECON 2011
We consider a variant of packet replay
attacks wherein, an attacker simply replays overheard frames as
they are, or with minor manipulations in the packet header; we
refer to this as the copycat attack. When routers forward such
replayed packets, the levels of congestion and interference increase
in large portions of the network. Our experiments indicate that
even a single attacker can degrade the route throughput by up
to 61%. While simple to use techniques such as digitally signing
every packet can stem the dissemination of such packets, they
are resource intense. Thus, we design a lightweight detection
and prevention system, COPS (for Copycat Online Prevention
System), that intelligently uses a combination of digital signatures
and Bloom filters to cope with the attack. With our system, the
task of identifying and discarding replayed packets is distributed
across a plurality of nodes on a route. We implement COPS
on real hardware and perform experiments on our 42 node
wireless testbed. Our measurements indicate that COPS achieves
its objective; it can efficiently contain the effects of replayed
packets to a local neighborhood without incurring high resource
consumption penalties. Specifically, we show that COPS reduces
the route throughput degradation by up to 66%.
Auto-configuration of 802.11n WLANs
ACM CoNEXT 2010
Channel Bonding (CB) combines two adjacent frequency
bands to form a new, wider band to facilitate high data rate
transmissions in MIMO-based 802.11n networks. However,
the use of a wider band with CB can exacerbate interference
effects. Furthermore, CB does not always provide benefits
in interference-free settings, and can even degrade performance
in some cases. We conduct an in-depth, experimental
study to understand the implications of CB. Based
on this study we design an auto-configuration framework,
ACORN, for enterprise 802.11n WLANs. ACORN integrates
the functions of user association and channel allocation,
since our study reveals that they are tightly coupled
when CB is used. We show that the channel allocation problem
with the constraints of CB is NP-complete. We implement ACORN on our 802.11n
testbed. Our experiments show that ACORN (i) outperforms
previous approaches that are agnostic to CB constraints; it
provides per-AP throughput gains from 1.5x to 6x.
On the Impact of MIMO Diversity on Higher Layer Performance
IEEE ICDCS 2010
We shed light on the cross-layer interactions between the PHY, link and routing layers in networks with MIMO links operating in
the diversity mode. Many previous studies assume an overly simplistic PHY layer model that does not sufficiently capture these
interactions. We show that the use of simplistic models can in fact lead to misleading conclusions with regards to the higher
layer performance with MIMO diversity. Towards understanding the impact of various PHY layer features on MIMO diversity, we begin
with a simple but widely-used model and progressively incorporate these features to create new models. We examine the goodness of
these models by comparing the simulated performance results with each, with measurements on an indoor 802.11n testbed. Our work
reveals several interesting cross-layer dependencies that affect the gains due to MIMO diversity. In particular, we observe that
relative to SISO links: (a) PHY layer gains due to MIMO diversity do not always carry over to the higher layers, (b) the use of
other PHY layer features such as FEC codes significantly influence the gains due to MIMO diversity, and (c) the choice of the routing
metric can impact the gains possible with MIMO.
Quantifying the Overhead due to Routing Probes in Multi-Rate WMNs
IEEE WCNC 2010
The selection of high-throughput routes is a key element towards improving the performance of wireless multihop networks. While several
routing metrics have been proposed in the literature, it has been shown that link-quality aware metrics can provide significantly
higher end-to-end throughput. To date, the online computation of such metrics requires the periodic transmission of probe packets at all
available transmission rates. However, our link level measurement study on two different 802.11 testbeds demonstrates that: (a) multi-rate
probe transmissions increase the number of collisions and enforce nodes to reside in the back-off state for prolonged time periods, and
(b) the extent of performance degradation depends on the network density; a network-wide throughput reduction of the order of 400% is possible.
In addition, our measurements show that the impact of probing in terms of end-to-end performance can be devastating. In particular, the probing
functionality can pose a significant degradation in the end-to-end throughput of a single flow, by at least 35% and as high as 90%, depending on
the probing frequency and network density. Finally, we discuss different alternatives to multi-rate probing for the online computation
of such metrics.
A Framework for Joint Network Coding and Transmission Rate Control in Wireless Networks
IEEE INFOCOM 2010
Network coding has been proposed as a technique that can potentially increase the transport capacity of a wireless network
via processing and mixing of data packets at intermediate routers. However, most previous studies either assume a fixed transmission
rate or do not consider the impact of using diverse rates on the network coding gain. Since in many cases, network coding implicitly
relies on overhearing, the choice of the transmission rate has a big impact on the achievable gains. The use of higher rates works in
favor of increasing the native throughput; however, it may in many cases work against effective overhearing. In other words, there is
a tension between the achievable network coding gain and the inherent rate gain possible on a link. Our goal in this work is to drive the
network towards achieving the best trade-off between these two contradictory effects. Towards this, we design a distributed framework that
(a) facilitates the choice of the best rate on each link while considering the need for overhearing and (b) dictates the choice of which
decoding recipient will acknowledge the reception of an encoded packet. We demonstrate that both of these features contribute significantly
towards gains in throughput. We extensively simulate our framework in a variety of topological settings. We also fully implement it on real
hardware and demonstrate its applicability and performance gains via proof-of-concept experiments on our wireless testbed. We show that our
framework yields throughput gains of up to 390% as compared to what is achieved in a rate-unaware network coding framework.
Topology Control for Effective Interference Cancellation in Multi-User MIMO Networks
IEEE INFOCOM 2010
In Multi-User MIMO networks, receivers decode multiple concurrent signals using Successive Interference Cancellation (SIC).
With SIC a weak target signal can be deciphered in the presence of stronger interfering signals. However, this is only
feasible if each strong interfering signal satisfies a signal-to-noise-plus-interference ratio (SINR) requirement. This
necessitates the appropriate selection of a subset of links that can be concurrently active in each receiver's neighborhood;
in other words, a sub-topology consisting of links that can be simultaneously active in the network is to be formed. If the
selected sub-topologies are of small size, the delay between the transmission opportunities on a link increases.
Thus, care should be taken to form a limited number of sub-topologies. We find that the problem of constructing the minimum
number of sub-topologies such that SIC decoding is successful with a desired probability threshold, is NP-hard.
Given this, we propose MUSIC, a framework that greedily forms and activates sub-topologies, in a way that favors successful SIC
decoding with a high probability. MUSIC also ensures that the number of selected sub-topologies is kept small. We provide both a
centralized and a distributed version of our framework. We prove that our centralized version approximates the optimal solution
for the considered problem. We also perform extensive simulations to demonstrate that (i) MUSIC forms a small number of sub-topologies
that enable efficient SIC operations; the number of sub-topologies formed is at most 17% larger than the optimum number of topologies,
discovered through exhaustive search (in small networks). (ii) MUSIC outperforms approaches that simply consider the number of antennas
as a measure for determining the links that can be simultaneously active. Specifically, MUSIC provides throughput improvements of up
to 4 times, as compared to such an approach, in various topological settings. The improvements can be directly attributable to a
significantly higher probability of correct SIC based decoding with MUSIC.
ARES: An Anti-jamming REinforcement System for 802.11 Networks
ACM CoNEXT 2009
Dense, unmanaged 802.11 deployments tempt saboteurs into launching jamming attacks by injecting malicious interference.
Nowadays, jammers can be portable devices that transmit intermittently at low power in order to conserve energy.
In this work, we first conduct extensive experiments on an indoor 802.11 network to assess the ability of two physical layer
functions, rate adaptation and power control, in mitigating jamming. In the presence of a jammer we find that: (a) the use of
popular rate adaptation algorithms can significantly degrade network performance and, (b) appropriate tuning of the carrier sensing
threshold allows a transmitter to send packets even when being jammed and enables a receiver capture the desired signal.
Based on our findings, we build ARES, an Anti-jamming REinforcement System, which tunes the parameters of rate adaptation and power
control to improve the performance in the presence of jammers. ARES ensures that operations under benign conditions are unaffected.
To demonstrate the effectiveness and generality of ARES, we evaluate it in different wireless testbeds.
We observe that ARES improves the network throughput across all testbeds by up to 150%.
Lightweight Jammer Localization in Wireless Networks: System Design and Implementation
IEEE GLOBECOM 2009
Jamming attacks have become prevalent during the last few years, due to the shared nature and the open access to the
wireless medium. Finding the location of a jamming device is of great importance for restoring normal network operations.
After detecting the malicious node we want to find its position, in order for further security actions to be taken. Our goal
in this work is the design and implementation of a simple, lightweight and generic localization algorithm. Our scheme is based
on the principles of the gradient descent minimization algorithm. The key observation is that the Packet Delivery Ratio (PDR)
has lower values as we move closer to the jammer. Hence, the use of a gradient-based scheme, operating on the discrete plane of
the network topology, can help locate the jamming device. The contributions of our work are the following: We demonstrate,
through analysis and experimentation, the way that the jamming effects propagate through the network in terms of the observed PDR.
We design a distributed, lightweight jammer localization system which does not require any modifications to the driver/firmware of
commercial NICs. We implement and evaluate our localization system on our 802.11 indoor testbed. An attractive and important feature
of our system is that it does not rely on special hardware.
FIJI: Fighting Implicit Jamming in 802.11 WLANs
ICST SECURECOMM 2009
The IEEE 802.11 protocol inherently provides the same long-term throughput to all the clients associated with a given
access point (AP). In this work, we first identify a clever, low-power jamming attack that can take advantage of this
behavioral trait: the placement of a low-power jammer in a way that it affects a single legitimate client can cause
starvation to all the other clients. In other words, the total throughput provided by the corresponding AP is drastically
degraded. To fight against this attack, we design FIJI, a cross-layer anti-jamming system that detects such intelligent
jammers and mitigates their impact on network performance. FIJI looks for anomalies in the AP load distribution to efficiently
perform jammer detection. It then makes decisions with regards to optimally shaping the traffic such that: (a) the clients that
are not explicitly jammed are shielded from experiencing starvation and, (b) the jammed clients receive the maximum possible
throughput under the given conditions. We implement FIJI in real hardware; we evaluate its efficacy through experiments on a
large-scale indoor testbed, under different traffic scenarios, network densities and jammer locations. Our measurements demonstrate
that FIJI detects such jammers in real-time and alleviates their impact by intelligently allocating the available bandwidth
in a fair and efficient way.
Routing-Aware Channel Selection in Multi-Radio Mesh Networks
IEEE ICC 2009
Efficient
channel selection is essential in 802.11 mesh deployments, for minimizing contention and interference among co-channel
devices and thereby supporting a plurality of QoS-sensitive applications. We propose ARACHNE,
a routing-aware channel selection protocol for wireless mesh networks. ARACHNE is distributed in nature, and
motivated by our measurements on a wireless testbed. The main novelty of our protocol comes from adopting a metric
that captures the end-to-end link loads across different routes in the network. ARACHNE prioritizes the assignment of
low-interference channels to links that (a) need to serve high-load aggregate traffic and/or (b) already suffer significant
levels of contention and interference. Our protocol takes into account the number of potential interfaces (radios) per
device, and allocates these interfaces in a manner that efficiently utilizes the available channel capacity. We evaluate
ARACHNE through extensive, trace-driven simulations. We observe that our protocol improves the total network
throughput, as compared to three other channel allocation strategies.
Design and Deployment Considerations for High Performance MIMO Testbeds
WICON 2008
MIMO (Multiple Input Multiple Output) enabled systems are characterized
by higher reliability and transmission rates, as compared to conventional
SISO (Single Input Single Output) systems. However, unless administered properly,
the MIMO technology may not facilitate very high throughputs on point-to-point
wireless links. Therefore, it becomes imperative for the network architect to design
such networks in ways that fully exploit the inherent properties of MIMO.
We first conduct an extensive experimental study, using a powerful
hardware platform, in order to understand the behavior of MIMO links in different
topological scenarios. Our experiments involve scenarios with MIMO links in isolation,
as well as in competition with other MIMO and SISO links. Second, we perform measurements
with different commercial platforms towards assessing the ability of each platform to
efficiently support the MIMO technology. Based on our experimental observations we deduce
that the CPU processing speed of the underlying hardware platform is an important factor
that can bound the maximum achievable throughput of a MIMO tranceiver. We comment on the
applicability of the different hardware choices that we test; furthemore, we suggest the
most appropriate choice for building a MIMO testbed, taking into account the cost, the
extendability and the reusability of the selected platform.
LAC: Load-Aware Channel Selection in 802.11 WLANs
IEEE PIMRC 2008
Dense deployments of hybrid WLANs result in high levels of
interference and low end-user throughput.
Many frequency allocation mechanisms for WLANs have been proposed
by a large body of previous studies.
However, none of these mechanisms considers the load that is carried
by APs in terms of channel conditions, number of affiliated
users as well as traffic-load, in conjunction.
In this work, we propose LAC, a load-aware channel allocation
scheme for WLANs, which considers all the above performance determinant factors.
LAC incorporates an airtime cost metric into its channel scanning process,
in order to capture the effects of these factors and select the channel
with the estimated maximum long-term throughput.
We evaluate LAC through extensive OPNET simulations, for many different traffic scenarios.
OPNET simulations demonstrate that LAC outperforms other frequency allocation
policies for WLANs in terms of total network throughput by up to 135%.
Assessing Link Quality in IEEE 802.11 Wireless Networks:
Which is the right metric?
IEEE PIMRC 2008
The accurate determination of the link quality is critical for ensuring that
functionalities such as intelligent routing, load-balancing, power control and
frequency selection operate efficiently.
There are 4 primary metrics for capturing the quality of a wireless link:
RSSI (Received Signal Strength Indication),
SINR (Signal-to-Interference-plus-Noise Ratio),
PDR (Packet-Delivery Ratio), and
BER (Bit-Error Rate).
We perform a measurement-based study in order to answer the question:
which is the appropriate metric to use, and under what conditions?
We evaluate the relative accuracy of each metric by conducting experiments with
multiple transmission rates and varying levels of interference on a large set of links.
We observe that each metric has advantages and projects one or more limitations.
Our study suggests that a careful consideration of these limitations is essential,
and provides guidelines on the applicability of each metric.
MDG: Measurement-Driven Guidelines for 802.11 WLAN Design
ACM MOBICOM 2007
Dense deployments of WLANs suffer from increased interference
and as a result, reduced capacity. There are three main functions
used to improve the overall network capacity: a) intelligent frequency
allocation across APs, b) load-balancing of user affiliations
across APs, and c) adaptive power-control for each AP. Several algorithms
have been proposed in each category, but so far, their evaluation
has been limited to: (a) each approach in isolation and, (b)
simulations or small-scale testbeds. In this work, we ask the question:
what is the best way to combine these different functions?
Our focus is to fully explore the interdependencies between the
three functions in order to understand when and how to deploy them
on a network. We follow a measurement-driven study to quantify
the effects of three previously proposed optimization schemes (one
for each category) on a relatively large testbed and in many different
scenarios. Surprisingly, we find that blindly applying all the
three optimization schemes is not always preferable; it can sometimes
degrade the performance by as much as 24% compared to
using only two of the schemes. We discover that there are explicit
conditions that are conducive for applying specific combinations
of the optimization schemes. We capture those conditions within
a comprehensive framework, which we call MDG (Measurement-
Driven Guidelines). While we derive such guidelines based on
measurements on one experimental testbed, we test their applicability
and efficacy on a second testbed in a different location. We show
that our framework improves network capacity consistently across
both testbeds, with improvements ranging from 22% to 142% with
802.11a, and 103% to 274% with 802.11g.
Implications of Power Control in Wireless Networks: A Quantitative Study
PAM 2007
The use of power control in wireless networks can lead to two conflicting
effects. An increase in the transmission power on a link may (i) improve
the quality and thus the throughput on that link but, (ii) increase the levels of interference
on other links. A decrease in the transmission power can have the opposite
effects. Our primary goal in this work is to understand the implications of
power control on interference and contention. We conduct experiments on an indoor
mesh network. Based on analysis of our experimental data, we identify three
interference scenarios: a) the overlapping case, where the aggregate throughput
achievable with two overlapping links cannot be improved via power control;
b) the hidden terminal case, where proper power control can primarily improve
fairness and, c) the potentially disjoint case, where proper power control can enable
simultaneous transmissions and thus improve throughput dramatically. We
find that power control can significantly improve overall throughput as well as
fairness. However, to our surprise, we note that using virtual carrier sensing in
conjunction with power control generally degrades performance, often to a large
degree.
A Blueprint for a Manageable and Affordable Wireless Testbed:
Design, Pitfalls and Lessons Learned
IEEE TRIDENTCOM 2007
We describe the deployment efforts
of our 802.11 indoor wireless testbed.We elucidate the challenges
that we faced and the design decisions that we had to make,
sometimes based on technical reasons, and other times due to
practicalities. These design challenges involve: (a) accessibility
to the software, in order to be able to modify and implement
various functionalities, (b) physical extendability, in order to
add hardware in the future and, (c) manageability, in order
to configure and update the software easily and quickly, for
all the nodes in the network. We justify the hardware and
software design choices that we make in order to facilitate these
requirements. For ease of maintenance and convenience, each
node is diskless, and we utilize power-over-ethernet through an
Ethernet connection with a central server. We ensure that the
software can be easily modified; this provides for easier module
implementation and parameter tuning. We explain the different
ways of node deployment, decisions that we make on power
settings and discuss how and why the receiver sensitivity affects
deployment decisions. Finally, we present our observations based
on a set of measurements to quantify the stability of the links
in our testbed.
Work on impulse-based UWB networks
CTU: Capturing Throughput Dependencies in UWB Networks
IEEE INFOCOM 2008
The inherent channel characteristics of impulse-based
UWB networks affect the MAC layer performance significantly.
However, previous studies on evaluating MAC protocols are based
on prolonged simulations, and most of them do not account for
the multiple-access interference that arises due to multipath delay
spread. In this work, we develop CTU, an analytical framework
that captures the performance of MAC protocols, while taking into
account these underlying PHY layer effects. The key attributes
that make CTU novel are: (a) It is modular and therefore flexible;
it can be easily modified to provide a basis for characterizing
and evaluating a wide range of MAC protocols designed for
impulse-based UWB networks. The only requirements are that
the MAC protocol under study be based on time-hopping, and
the modulation scheme be pulse position modulation; these are
common design decisions in most impulse based UWB networks.
(b) It considers the channel characteristics in addition to MAC
layer effects; in particular, CTU correlates probabilistically the
multipath delay profile of the channel with the packet error rate.
We employ CTU to evaluate the performance of a generic medium
access procedure.We compare the results with those from extensive
simulations and show the high accuracy of CTU. We use CTU to
assess the impact of various system parameters on the MAC layer
performance; we make several interesting observations that are
discussed in depth.
On the MAC Layer Performance of Time-Hopped UWB Ad Hoc Networks
IEEE ICCCN 2006
In this work, we present our efforts on investigating the impact of the multipath delay spread
on the MAC layer performance of time-hopped impulse-based
UWB ad hoc networks. We discuss a simplified channel model for
the multipath delay spread and we simulate a single-band MAC
protocol which employs binary pulse position modulation. Our
simulation results demonstrate that the performance is determined
by the properties of the time hopping sequences of the nodes. We
observe that the right parameter values depend on the number of
nodes deployed, and the delay spread experienced. If the topology
changes dynamically, adaptive strategies for varying system
parameters are required for achieving the best performance.
Multiband Media Access Control in Impulse-Based UWB Ad Hoc Networks
IEEE Transactions on Mobile Computing, April 2007
We propose a MAC protocol for use in multihop wireless networks that
deploy an underlying UWB-based physical layer. We consider a multiband
approach to better utilize the available spectrum, where each transmitter
sends longer pulses in one of many narrower frequency bands. The motivation
comes from the observation that, in the absence of a sophisticated equalizer,
the size of a slot for transmitting a UWB pulse is typically dictated by the
delay spread of the channel. Therefore, using a wider frequency band to shorten
the transmission time for each pulse does not increase the data rate in proportion
to the available bandwidth. Our approach allows data transmissions to be contiguous
and practically interference free, and, thus, highly efficient. For practicality,
we ensure the conformance of our approach to FCC-imposed emission limits.
We evaluate our approach via extensive simulations, and our results demonstrate the
significant advantages of our approach over single-band solutions: The throughput
increases significantly and the number of collisions decreases considerably. Finally,
we analyze the behavior of our MAC protocol in a single-hop setting in terms of its
efficiency in utilizing the multiple bands.
A New Binary Conflict Resolution-Based MAC Protocol for
Impulse-Based UWB Ad Hoc Networks
Wireless Comm. and Mobile Comp., Nov. 2006
We propose a novel multi-band MAC protocol for use in small ad hoc networks that
deploy an underlying UWB based physical layer. In our approach, we divide the
available UWB bandwidth into multiple simultaneously usable bands. A multi-band
approach that uses a plurality of bands that adhere to FCC specifications, with
slightly elongated pulse durations, provides a solution that can effectively utilize the UWB
spectrum. Our approach is based on the idea of conflict resolution using binary
something/nothing feedback, which has not been widely studied in wireless and
specifically in UWB networks. Our protocol unites binary conflict resolution and
multi-band utilization to effectively utilize the available bandwidth. To ensure that our
proposed approach is tightly knit with the underlying physical layer, we discuss
physical–layer dependencies and the conformance to FCC-imposed emission limits.
Miscellaneous projects
Overcoming the Challenge of Security in a Mobile Environment
IEEE IPCCC 2006
The secure operation of ad hoc networks faces
the novel challenge of location verifcation on top of the security
challenges that wireline networks face. The novelty
lies in the fact that a node can correctly validate who it is,
but lie about its location and exploit this to create problems
to the network. There are three main factors that make
ad hoc networks more vulnerable: (a) nodes can overhear
other nodes announcements, (b) nodes can lie about their
location, and (c) nodes can avoid detection and isolation by
moving. As a result, malicious nodes can fake their position
and this way obstruct the routing. In this work, we
explain how location and topology related malice can affect
the security of wireless ad hoc networks. First, we present
the most important attacks that can stem from misuse of
location information. Second, we provide an overview of security
routing approaches. Although several of the current
techniques are promising, we conclude that there does not
exist a bulletproof approach as of yet.
A Comprehensive Comparison of Routing Protocols for Large-Scale Wireless MANETs
IEEE IWWAN/SECON 2006
Efficient routing protocols can provide significant
benefits to mobile ad hoc networks, in terms of both
performance and reliability. Many routing protocols for
such networks have been proposed so far. Amongst the
most popular ones are Dynamic Source Routing (DSR),
Ad hoc On-demand Distance Vector (AODV), Temporally-
Ordered Routing Algorithm (TORA) and Location-Aided
Routing (LAR). Despite the popularity of those protocols,
research efforts have not focused in evaluating
their performance when applied to large-scale wireless
networks. Such networks are comprised of hundreds of
nodes, connected via long routes. This greatly affects the
network efficiency, since it necessitates frequent exchange
of routing information. We present our
observations regarding the behavior of the above protocols,
in large-scale mobile ad hoc networks (MANETs). We
consider wireless mobile terminals spread over a large
geographical area, and we perform extensive simulations,
using the QualNet and NS-2 simulators. The results of
the simulations yield some interesting conclusions: AODV
suffers in terms of packet delivery fraction (PDF) but
scales very well in terms of end-to-end delay. DSR on
the other hand scales well in terms of packet delivery
fraction but suffers an important increase of end-to-end
delay, as compared to its performance achieved in smallscale
topologies. Also, the effect of maximum connections
is severe on TORA, which seems unable to route large
amounts of traffic. LAR, seems to scale very well, in terms
of all metrics employed.
Handling Asymmetry in Gain in Directional Antenna Equipped Ad Hoc Networks
IEEE PIMRC 2005
The deployment of directional antennae in ad hoc
networks offers a number of benefits over deploying the
vanilla omni-directional antennae; these benefits include
increased spatial reuse and increased directional range of
coverage. However, the deployment of traditional higher
layer protocols (especially the IEEE 802.11 MAC protocol at
the MAC layer) with directional antennae could lead to
problems from an increased number of collisions; this effect
is primarily seen due to three specific effects: (i) an increase
in the number of hidden terminals; (ii) the problem of
deafness and, (iii) a difficulty in determining the locations of
neighbors. In this work we propose a new MAC protocol that
incorporates circular RTS and CTS transmissions. We show
that the circular transmission of the control messages helps
avoid collisions of both DATA and ACK packets from hidden
terminals. Our protocol intelligently determines the
directions in which the control messages ought to be
transmitted so as to eliminate redundant transmissions in
any given direction. We perform extensive simulations and
analyze the obtained results in order to compare our scheme
with previously proposed protocols that have been proposed
for use in directional antenna equipped ad hoc networks.
Our simulation results clearly demonstrate the benefits of
incorporating both circular RTS and CTS messages in terms
of the achieved aggregate throughput.
On the Feasibility of Integrated MPEG Teleconference and
Data Transmission, over IEEE 802.11 WLANs
Networking 2004
We present and discuss the results from simulation experiments we
performed in order to evaluate the 802.11 protocol performance.
We study traffic scenarios of integrated MPEG teleconference and
computer data transmissions, over the IEEE 802.11b WLAN.
Our simulation results clearly demonstrate the difficulty of the
protocol to support time sensitive applications with a moderate number
of wireless users under the same Access Point.
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