I am a Faculty Research Associate in the
Dept of Computer Science, University of Maryland
College Park.
Through my research, I have explored various aspects of computer networking and
distributed systems. My research interests are in protocols, services, and
architectures for mobile/wireless networks and ubiquitous computing
environments. My work covers different layers of the protocol stack from the
physical layer up to the application layer. Specific research projects target
location determination systems, sensor networks, protocol modeling and analysis,
peer-to-peer systems, network measurements, and security.
List of Publications
The following is a list of the different projects that I have worked on:
The proposed scheme works by first assuming a local clock model at each node that takes the clock offset and drift rate into account. Timestamps are exchanged between neighboring nodes which permit each node to derive a common time base using only its local information. The mathematical basis of the approach comes from linear algebra, in which the principal eigenvector of a stochastic matrix can be calculated by repeated multiplications of matrices.
Cyclone also defines the notion of a common Virtual Clock. Cyclone allows all nodes to calculate the parameters, drift rate and offset, for a virtual clock such that any node can convert its clock readings to the reading of the common virtual clock at any time instant, even through different nodes’ local clock reading may be widely different.
Our initial results show that we can achieve a stable and high degree of
clock synchronization. The degree of synchronization achieved is affected by the
perturbations in both (i) the transit time and (ii) the clock drift rate, but
does not depend on the clock drift rate.
The Cyclone Time Technology
(with Bao Trinh and Ashok Agrawala)
US-Patent pending.
PinPoint: An Asynchronous Time-Based Location Determination System
With Ashok Agrawala, Professor, Dept of Computer Science University of Maryland, College ParkThe PinPoint Technology
US-Patent pending.
Rover II: An Information Dynamics-Based Context Aware Platform
With Ashok Agrawala, Professor, Dept of Computer Science University of Maryland, College Park
Horus: A WLAN Location Determination System
With Ashok Agrawala, Professor, Dept of Computer Science University of Maryland, College ParkOur research focuses on identifying the noisy characteristics of the wireless channel and developing techniques to overcome them to obtain accurate positioning. It is advantageous to run the location determination algorithm on the client devices to achieve privacy and decentralized implementation. Since these devices are usually energy constrained, it is important to reduce the computation requirements for location determination algorithms. We have developed location-clustering techniques based on the signal strength received from the access points to reduce the computational requirements of the location determination algorithm and allow the system to scale to large areas.
The Horus system has been used in other research projects such as the Rover system and the Location Based Authentication project. The Horus system has been tested in areas as large as 20,000 square feet and the accuracy is 2.5 feet on the average for different testbeds.
As part of our work, we developed device drivers to query the wireless card and API's to make the Horus system independent of the underlying device driver/card. Our software has been used by other wireless researchers around the world.
Currently, we are looking into techniques to ensure user privacy even if the user is communicating with the system and the signal strength from his device can be recorded by the system. As part of our ongoing work we are experimenting with different clustering techniques, automating the radio-map generation process, developing applications and services over Horus, dynamically changing the system parameters, and finding the optimal placement of access points to achieve maximum accuracy.
On the Optimality
of WLAN Location Determination Systems
(with Ashok Agrawala)
CS-TR 4459, Department of Computer Science, University of Maryland, College
Park, March 2003.
Horus: An RF-Based Location Determination System
(with Ashok Agrawala)
University of Maryland, College Park, March 2003.
Probabilistic
Clustering-Based Indoor Location Determination System
(with Ashok Agrawala, A. Udaya Shankar)
CS-TR 4350, Department of Computer Science, University of Maryland, College
Park, March 2002.
Rover: Location-Aware Computing for Wireless Environments
With Ashok Agrawala and A. Udaya Shankar, Professors, Dept of Computer Science University of Maryland, College ParkThe Rover server interacts with the clients to provide and manage the different service requests from the Rover-clients. To scale the Rover server operations to a very large client set, we have defined a new Action model which allows fine-grained, real-time scheduling of server operations.
Apart from system design, I have also been involved in project with a team of other students in implementing different aspects of the system.
We have implemented and demonstrated both outdoors and indoors version of Rover. In the outdoor case, we used a GPS unit attached the the clients to provide location service. It had an accuracy of less than 3 meters. For the indoor case, the location was based on an earlier version of the Horus system.
Many studies on measurement and characterization of wireless LANs have been
performed recently. Most of these
measurements have been conducted from the wired portion of the network based on
wired monitoring or SNMP statistics. In
the wireless traffic characterization project, we argue that traffic
measurements from a wireless
vantage point in the network are more appropriate than wired measurements or
SNMP statistics, to expose the wireless medium
characteristics and their impact on the traffic patterns. While it is easier to
make consistent measurements in the wired part of
a network, such measurements can not observe the significant vagaries present in
the wireless medium itself. As a consequence
constructing an accurate measurement system from a wireless vantage point is
important but usually quite difficult due to the
noisy wireless channel.
In our work we have explored the various issues in implementing such a system
to monitor traffic in an
IEEE 802.11 based wireless network. Our analysis reveals rich information about
the PHY/MAC layers of the
IEEE 802.11 protocol such as the typical traffic mix of different frame types,
their temporal characteristics, correlation with
the user activities and the error characteristics of the wireless medium.
Moreover, we identify anomalies in the operation of
the IEEE 802.11 MAC protocol.
Another technology that we implemented to enhance the 802.11 security model is Koolspan. In Koolspan, user authentication is performed through smartcard-based physical tokens. The Koolspan Client Key secures wireless traffic by connecting to Koolspan SecurEdge Unilock installed behind the access point. A major goal for Koolspan is to be transparent to the standard 802.11 access points and clients, allowing easy integration with the current installed networks.
Energy Efficient Wireless (Sensor) Networks
With Mohammed Younis, Professor, Dept of Computer Science University of Maryland, Baltimore County
Our work focuses on balancing different performance
metrics. By changing system parameters, different systems can achieve different
performance objectives depending on the mission assigned to the sensor network.
We designed a routing protocol that selectively turns sensor nodes on or off based on the individual nodes' energy state and on the the global system performance requirements. The routing decisions are changes based on events in the system such as target movement or a drop of the energy of a node below a threshold. We showed that our routing protocol achieve significant improvement is performance over the current energy efficient protocols without sacrificing energy efficiency.
We also experimented with different energy-efficient TDMA MAC layer protocols and designed techniques for assigning slots to obtain better throughput and less changes in the state of the wireless card circuitry.
Current extensions to our work include designing clustering algorithms for sensor networks and implementing the mechanisms in a real world multi-hop wireless network. .
with Liviu Iftode, Associate Professor, Dept of Computer Science,
Rutgers University.
In this work we consider the design principles of the Instance-Based Network (IBN),
an extended version of a generic Content-Based Network (CBN). IBN acts as an overlay
communication platform over which end-point entities, called contents, communicate
independently from their physical locations while providing the flexibility of having
different instances of the same content. The semantics of different instances are
assigned by the application using the IBN. Routing in the IBN is instance-based;
the IBN can route a message to a specific content instance or to the closest instance,
if no exact match is found for the destination content instance. Moreover, the IBN
replicates the stored contents in order to provide fault tolerance.
Possible applications for the IBN applications include:
a file archiving system over a peer-to-peer network. Files in this system are defined by content identifiers and the system keeps track of different versions of the same file. A user of such a system can request to retrieve a specific version of the file or can request the latest version stored in the system. The file archiving system is an example of a larger class of peer-to-peer applications where entities (files in the file archiving system) are defined by content identifiers (file names) and different instances (file versions) of the same content can exist at the same time.
We have developed an implementation prototype based on Pastry as the underlying peer-to-peer lookup service.
Currently, we are working on evaluating the performance of the IBN, implementing applications over it, and experimenting with different underlying infrastructures.
with Liviu Iftode, Associate Professor, Dept of Computer Science, Rutgers University.
The basic service provided by the Autonomous Transport Protocol (ATP) is a reliable transport connection between two endpoints, identified by content identifiers, independent of their physical location. Autonomy allows dynamic endpoints relocation on different end hosts without disrupting the transport connection between them. ATP depends on the existence of an underlying Instance Based Network (IBN) to achieve its goals. ATP layers at the intermediate nodes can actively participate in the connection. Data is transferred by a combination of active and passive operations, where the ATP layer of a node can decide whether to actively push the data to the destination or to passively wait for the destination endpoint to pull the data. The decision to whether to use the active or passive modes can be taken by a local policy on the node running the ATP protocol.
Current research directions include designing and evaluating different policies for the pull/push decision, designing and implementing applications over ATP, and enhancing the protocols to increase system security.
We solve the location determination and authentication problem using the Horus system. Results from actual wireless experiments show the feasibility of this scheme.
For this branch of my networking research, we have been working on formally modeling different networking protocols and analyzing their properties.
We modeled the IEEE 802.11 protocol using the systems of communicating machine approach. We also analyzed the model and confirmed that it is free from deadlocks, unspecified receptions, non-executable transitions. Moreover, we showed that the model have some desirable liveness properties.
We are
currently working on the passive testing problem where a system can be tested passively
in order to detect, identify and locate faults.
| Last updated on Tuesday, 24. October 2006 | -- Moustafa |