Communication and Internet Research Lab

TCP Performance Improvements
Sensor Networks
Heterogeneous Wireless Networks
Data Availability of Higher-level User Tasks
Defending against Sybil Attacks in Decentralized Distributed Systems
Obtaining Secure Aggregate Information in Sensor Networks
Geographic Routing in Wireless Networks

TCP Performance Improvements

In this area of research, we study the dynamics of TCP protocol and its adaptation to the emerging wireless networks which are known for high loss and round-trip time. We have just initiated a project called “Reactive Transport Service” in which we intend to do basic research to understand the dynamics of transport layer protocols in the context of mobile wireless environment of an All-IP converged network and the characteristics of access networks and mobility pattern of the Internet enabled devices, and to come up with heuristics that could be applied to the design of algorithms capable of learning and reacting to the heterogeneous and dynamic nature of the network. The findings could be applied to improve the performance of transport service, and to design an intelligent and adaptive transport layer protocols that would be required in the converged heterogeneous networks of the future.

Representative Publications:
1. Xiuchao Wu, Mun Choon Chan and A.L.Ananda, “TCP HandOff: A Practical TCP Enhancement for Heterogeneous Mobile Environments”, to be presented at the ICC at Glasgow, 24-27 June 2007.
2. Xiuchao Wu, A. L. Ananda and Mun Choon Chan, PMC: An Energy Efficient Event Transport Service for Wireless Sensor Network, Proceedings of 2006 IEEE Interntional Conference on Communications (2006). USA: IEEE Interntional Conference on Communications, 11 – 15 Jun 2006, Instanbul, Turkey.
3. Venkatesh, S O, Lillykutty Jacob and A L Ananda, "Secure Performance Enhancing Proxy: To Ensure End-to-End Security and Enhance TCP Performance over IPv6 Wireless Networks". Computer Networks, 50, no. 13 (monthly) (2006): 2225-2238. (Netherlands).
4. Xiuchao Wu, Indradeep Biswas, Mun Choon Chan, A.L. Ananda , Utilizing Characteristics of Last Link to Improve TCP Performance, in the proceedings of the 24th IEEE International Performance Computing and Communications Conference, Phoenix, Arizona, April 7-9 2005, pp 207-214, USA.

A FRC grant of $138,000 has been obtained for this research work.

Sensor Networks

With the capability to construct low power and low cost devices that support sensing, computation and communication capabilities, it is possible to create new and exciting types of applications in a wide range of areas including transportation, manufacturing, health care, environmental oversight, and safety and security.

Due to constraints of sensor nodes, many of the networking issues like MAC, network and transport protocols have to be revisited. In particular, protocols for sensor networks have to be very energy efficient. In order to reduce energy consumptions, two techniques can be applied. The technique is the idea of cross-layer design where the physical, MAC, network and transport protocols are designed in an integrated way so that better energy efficiency can be obtained. Second, sensor networks are often application specified. Hence, the application requirements are often reflected in the networking optimization process.

We are interested in investigating into the cross-layer design issue and are also building novel and practical sensor network system to guide and verify the design.

Representative Publications:
1. Shao Tao, A.L. Ananda and Mun Choon Chan, "Greedy Face Routing with Face ID Support," IEEE ICCCN, August 13 - 16 2007, Turtle Bay Resort, Honolulu, Hawaii, USA.
2. Mingze Zhang, Mun Choon Chan and A.L. Ananda, "Coverage Protocol for Wireless Sensor Networks Using Distance Estimates," IEEE SECON, June 18-21, 2007, San Diego, California, USA.
3. Eugene Chai, Mun Choon Chan and A.L. Ananda, "Coverage Aware Buffer Management and Scheduling for Wireless Sensor Network," IEEE SECON 2006, Reston, VA, Sep 25-28, 2006. <http://www.comp.nus.edu.sg/%7Echanmc/papers/secon.pdf>

A URC grant of $200,000 has been obtained for this research work.

Heterogeneous Wireless Networks

Development in new radio technologies and increase in user demand are driving the deployment of a wide array of wireless networks, ranging from 802.11 networks in the local area, to third generation data-only wireless networks in the wide area. Such a diverse set of wireless networks poses a number of interesting issues. We are mainly interested in the resource management related to heterogeneous wireless networks. We consider the case where multiple wireless networks, including 802.11, 802.16 and 3G data-only networks are being deployed and a single wireless provider owns and operates these wireless networks. We are interested in how a network manager can efficiently manage the common pool of radio resources, and how the quality of service of real-time applications (such as voice) and completion time of short data transfer be improved through redundant transmission.

Representative Publications:
1. Mun Choon Chan and Ram Ramjee, "Improving TCP/IP Performance over Third Generation Wireless Networks," accepted for publications in IEEE Transactions of Mobile Computing.
2. Tian Bu, Mun Choon Chan and Ram Ramjee, "Connectivity, Performance, and Resiliency of IP-Based CDMA Radio Access Networks," IEEE Transactions on Mobile Computing, August 2006 (Vol. 5, No. 8), pp. 1103-1118. <http://www.comp.nus.edu.sg/%7Echanmc/papers/tmc2006.pdf>
3. Binbin Chen and Mun Choon Chan, "Proportional Fairness for Overlapping Cells in Wireless Networks," VTC Fall, Montreal, Sep. 2006. <http://www.comp.nus.edu.sg/%7Echanmc/papers/vtc2006.pdf>
4. Binbin Chen and Mun Choon Chan, "Resource Management in Heterogeneous Wireless Networks with Overlapping Coverage," COMSWARE, New Delhi, Jan 2006. <http://www.comp.nus.edu.sg/%7Echanmc/papers/comsware2006.pdf>

The work is supported by a research grants totaling around $75,000.

Data Availability of Higher-level User Tasks

Data replication is a key technique to ensure data availability in the presence of machine failures. Most previous work on data availability focuses on the availability of a single data object (e.g., a single file). A higher-level user operation, however, often needs to access multiple data objects to perform a certain task. Our research reveals that the relative placement or assignment of the replicas of different objects can result in subtle correlation among objects and dramatic effects on system availability.
Using strong probabilistic tools such as Janson's inequality from random graph theory, we are able to find the optimal assignment under different settings. We have also proposed practical decentralized designs to approximate these optimal assignments in practice, and implement the design in a prototype wide-area storage system called MOAT. PlanetLab deployment and simulation results show that using the appropriate assignment often decreases failure probability of operations by multiple orders of magnitude.

Representative Publications:
1. Haifeng Yu and Phillip B. Gibbons, "Optimal Inter-Object Correlation When Replicating for Availability." Proceedings of the 26th ACM Symposium on Principles of Distributed Computing (PODC'07), August 2007.
2. Jeffrey Pang, Phillip B. Gibbons, Michael Kaminsky, Srinivasan Seshan, and Haifeng Yu, "Defragmenting DHT-based Distributed File Systems." Proceedings of International Conference on Distributed Computing Systems (ICDCS'07), June 2007.
3. Haifeng Yu, Phillip B. Gibbons, and Suman Nath, "Availability of Multi-Object Operations." Proceedings of the Symposium on Networked Systems Design and Implementation (NSDI'06) , May 2006.

Defending against Sybil Attacks in Decentralized Distributed Systems

Peer-to-peer and other decentralized, distributed systems are known to be particularly vulnerable to {\em sybil attacks}. In a sybil attack, a malicious user obtains multiple fake identities and pretends to be multiple, distinct nodes in the system. By controlling a large fraction of the nodes in the system, the malicious user is able to ``out vote'' the honest users in collaborative tasks such as Byzantine failure defenses. We have proposed
SybilGuard, a novel protocol for limiting the corruptive influences of sybil attacks. SybilGuard is based on the ``social network'' among user identities, where an edge between two identities indicates a human-established trust relationship. Malicious users can create many identities but few trust relationships. Thus, there is a disproportionately-small ``cut'' in the graph between the sybil nodes and the honest nodes. SybilGuard exploits this property to bound the number of identities a malicious user can create.

Representative Publications:
1. Haifeng Yu, Michael Kaminsky, Phillip B. Gibbons, and Abraham Flaxman, "SybilGuard: Defending Against Sybil Attacks via Social Networks." Proceedings of ACM SIGCOMM Conference , September 2006.

Obtaining Secure Aggregate Information in Sensor Networks

Wireless sensor networks are often queried for aggregates such as predicate count and sum. Since sensors may potentially be compromised, there is a clear need for security. Previous approaches for secure aggregation queries mainly focus on ensuring that the base station does not accept incorrect result. On the other hand, it is possible for the base station not to obtain any result at all.
This project argues that such guarantee is often not sufficient because otherwise adversary presence will prevent the computing of the aggregate forever, which is equivalent to a global DoS attack. To address such problem, we are currently exploring two novel protocols for secure aggregation queries in sensor networks that enable the base station to obtain a correct result despite adversary presence. To achieve our goal, the two protocols depart from the traditional tree-based in-network aggregation paradigm and leverage unique insights into synopsis diffusion and sampling.

Representative Publications:
1. Haifeng Yu, "Brief Announcement: DoS-Resilient Secure Aggregation Queries in Sensor Networks." Proceedings of the 26th ACM Symposium on Principles of Distributed Computing (PODC'07), August 2007.

Geographic Routing in Wireless Networks (website)

As wireless sensor networks continue to grow in size, we are faced with the prospect of emerging wireless networks with hundreds or thousands of nodes. While earlier generations of such networks employed routing protocols that did not require a point-to-point routing primitive, geographic routing algorithms have recently been proposed as a new routing primitive for data-centric storage and for running more complex queries over such networks. In this project, we seek to develop and evaluate new techniques in geographic routing and to understand the relative tradeoffs between geographic routing algorithms and ad hoc routing algorithms like DSR, DSDV and AODV.

Representative Publications:
1. Ben Leong, Sayan Mitra, and Barbara Liskov, "Path Vector Face Routing: Geographic Routing with Local Face Information". Proceedings of the 13th IEEE International Conference on Network Protocols (ICNP 2005). Boston, MA, November 2005.
2. Ben Leong, Barbara Liskov, and Robert Morris, "Geographic Routing without Planarization". Proceedings of the 3rd Symposium on Network Systems Design and Implementation (NSDI 2006). San Jose, CA, May 2006.
3. Ben Leong, Barbara Liskov, and Robert Morris, "Greedy Coordinates for Geographic Routing". Proceedings of the 15th IEEE International Conference on Network Protocols (ICNP 2007), Beijing, China, October 2007.

Research Areas