Ranveer Chandra's Research
The goal of my research is to improve the user experience over wireless networks to make it comparable, if not better than his experience over wired networks.
Existing wireless networks suffer from low capacity, high loss rates, susceptibility to security threats, and all these limitations are exacerbated by a poor infrastructure for performing fault diagnosis and management in such networks. I have worked on overcoming the above limitations in wireless networks, and providing new functionality for a better user experience through the following research projects:
See the MultiNet
(now VirtualWiFi) webpage for more details about this project, and for downloading the software.
There are a number of scenarios where it is desirable to have a wireless device connect to multiple networks simultaneously. Currently, this is possible only by using multiple wireless network cards in the device. Unfortunately, using multiple wireless cards causes excessive energy drain and consequent reduction of lifetime in battery operated devices. In this paper, we propose a software based approach, called MultiNet, that facilitates simultaneous connections to multiple networks by virtualizing a single wireless card. The wireless card is virtualized by introducing an intermediate layer below IP, which continuously switches the card across multiple networks. The goal of the switching algorithm is to be transparent to the user who sees her machine as being connected to multiple networks. We present the design, implementation, and performance of the MultiNet system. We analyze and evaluate buffering and switching algorithms in terms of delay and energy consumption. Our system is agnostic of the upper layer protocols, and works well over popular IEEE 802.11 wireless LAN cards.
See the SSCH overview for more details about this protocol, and go to the SSCH webpage page to download the SSCH implementation in Qualnet.
Capacity improvement is one of the principal challenges in wireless
We present a link-layer protocol called Slotted Seeded Channel
Hopping, or SSCH, that increases the capacity of an IEEE 802.11 network
by utilizing frequency diversity.
SSCH can be implemented in
software over an IEEE 802.11-compliant wireless card.
Each node using SSCH switches across
channels in such a manner that nodes desiring to communicate
overlap, while disjoint communications do not overlap, and hence
do not interfere with each other. To achieve this, SSCH uses a novel
scheme for distributed rendezvous and synchronization. Simulation
results show that SSCH significantly increases network capacity in
several multi-hop and single-hop wireless networking scenarios.
Wireless Fault Diagnosis
The wide-scale deployment of IEEE 802.11 wireless networks has generated
significant challenges for Information Technology (IT) departments in
corporations. Users frequently complain about connectivity and performance
problems, and network administrators are expected to diagnose these problems
while managing corporate security and coverage. Their task is particularly
difficult due to the unreliable nature of the wireless medium and a lack of
intelligent diagnostic tools for determining the cause of these problems.
This paper presents an architecture for detecting and diagnosing faults in
IEEE 802.11 infrastructure wireless networks. To the best of our knowledge,
ours is the first paper to address fault diagnostic issues for these
networks. As part of our architecture, we propose and evaluate a novel
technique called Client Conduit, which enables bootstrapping and
fault diagnosis of disconnected clients. We describe techniques for
analyzing performance problems faced in a wireless LAN deployment. We also
present an approach for detecting unauthorized access points. We have
built a prototype of our fault diagnostic architecture on the Windows
operating system using off-the-shelf IEEE 802.11 cards. The initial results
show that our mechanisms are effective; furthermore, they impose low
overheads when clients are not experiencing problems.
Efficient integration of a multi-hop wireless network with the Internet is an important research problem.
In a wireless neighborhood network, a few Internet Transit Access Points (ITAPs), serving as gateways to the Internet, are deployed across the neighborhood; houses are equipped with low-cost antennas, and form a multi-hop wireless network among themselves to cooperatively route traffic to the Internet through the ITAPs.
Furthermore, the placement of Internet TAPs is a critical determinant of system performance and resource usage.
In this paper, we explore the placement problem under three wireless link models. For each link model, we develop algorithms to make informed placement decisions based on neighborhood layouts, user demands, and wireless link characteristics. We also extend our algorithms to provide fault tolerance and handle significant workload variation. We evaluate our placement algorithms
and show that our algorithms yield close to optimal solutions over a wide range of scenarios we have considered.
Wireless Topology Discovery
Wireless networks in home, office and sensor applications consist
of nodes with low mobility. Most of these networks have at least
a few powerful machines additionally connected by a wireline network.
Topology information of the wireless network at these powerful nodes
can be used to control transmission power, avoid congestion, compute
routing tables, discover resources, and to gather data. In this paper
we propose an algorithm for topology discovery in wireless networks
with slow moving nodes and present various performance characteristics
of this algorithm. The proposed algorithm discovers all links and
nodes in a stable wireless network and has an excellent message
complexity: the algorithm has an optimal message complexity in a
stable network and the overhead degrades slowly with increasing
mobility of the nodes.
Sub Routing Layer
Several routing protocols for mobile ad hoc networks work efficiently only in bi
Unidirectional links may exist in a real network due to heterogeneity in transmi
ssion power of different nodes, noise, and other signal propagation phenomena.
We introduce a sub-layer called Sub Routing Layer, SRL, between the network and the MAC layer to provide a bidirectional abstraction of the unidirectional network to the routing protocols. We present a scalable and efficient way to provide this abstraction by finding and maintaining multi-hop reverse routes to each unidirectional link. We simulate SRL and a modified version of AODV that uses SRL to route packets in unidirectional networks. We observed that with SRL, the packet delivery of AODV in unidirectional networks increases substantially. Further, our simulations indicate that reverse routes are often only a few hops long and hence the overhead of SRL is very low.
In recent years, a number of applications of ad-hoc networks have been proposed. Many of them are based on the availibilty of a robust and reliable multicast protocol. In this paper, we address the issue of reliability and propose a scalable method to improve packet delivery of multicast routing protocols and decrease the variation in the number of packets received by different nodes. The proposed protocol works in two phases. In the first phase, any suitable protocol is used to multicast a message to the group, while in the second concurrent phase, the gossip protocol tries to recover lost messages. Our proposed gossip protocol is called Anonymous Gossip(AG) since nodes need not know the other group members for gossip to be successful. This is extremely desirable for mobile nodes, that have limited resources, and where the knowledge of group membership is difficult to obtain. As a first step, anonymous gossip is implemented over MAODV without much overhead and its performance is studied. Simulations show that the packet delivery of MAODV is significantly improved and the variation in number of packets delivered is decreased.
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