Shankar M. Banik

Multicast Routing with Delay and Delay Variation Constraints for Collaborative Applications on Overlay Networks

Computer supported collaborative applications on overlay networks are gaining popularity among users who are geographically dispersed. Examples of these kinds of applications include video-conferencing, distributed database replication, and online games. This type of application requires a multicasting subnetwork, using which messages should arrive at the destinations within a specified delay bound. These applications also require that destinations receive the message from the source at approximately the same time. The problem of finding a multicasting subnetwork with delay and delay-variation bound has been proved to be an NP complete problem in the literature and heuristics have been proposed for this problem. In this paper, we provide an efficient heuristic to obtain a multicast subnetwork on an overlay network, given a source and a set of destinations that is within a specified maximum delay and a specified maximum variation in the delays from a source to the destinations. The time-complexity of our algorithm is O(|E|+nk log(|E|/n)+m2k), where n and |E| are the number of nodes and edges in the network, respectively, k is the number of shortest paths determined, and m is the number of destinations. We have shown that our algorithm is significantly better in terms of time-complexity than existing algorithms for the same problem. Our extensive empirical studies indicate that our heuristic uses significantly less runtime in comparison with the best-known heuristics while achieving the tightest delay variation for a given end-to-end delay bound

A power-aware technique to manage real-time database transactions in mobile ad-hoc networks

A mobile ad-hoc network (AMNET) is a collection of wireless autonomous mobile hosts which are free to move randomly, thus forming a temporary network without any fixed backbone infrastructure. AMNET is typically used in battlefields and disaster recovery situations where temporary network connectivity is required Techniques that manage database transactions in AMNET need to address additional issues such as host mobility, energy limitation and real-time constraints. The paper proposes a solution for transaction management that reduces the number of transactions missing deadlines while balancing the energy consumption by the mobile hosts in the system. The paper then presents a performance study by means of simulation.

Managing real-time database transactions in mobile ad-hoc networks

In a mobile ad-hoc network (MANET), mobile hosts can move freely and communicate with each other directly through a wireless medium without the existence of a fixed wired infrastructure. MANET is typically used in battlefields and disaster recovery situations where it is not feasible to have a fixed network. Techniques that manage database transactions in MANET need to address additional issues such as host mobility, energy limitation and real-time constraints. This paper proposes a solution for transaction management that reduces the number of transactions missing deadlines while balancing the energy consumption by the mobile hosts in the system. This paper then reports the simulation experiments that were conducted to evaluate the performance of the proposed solution in terms of number of transactions missing deadlines, total energy consumption and the distribution of energy consumption among mobile hosts.

Distributed floor control protocols for computer collaborative applications on overlay networks

Computer supported collaborative applications on overlay networks are gaining popularity among users who are geographically dispersed. Examples of these kinds of applications include video-conferencing, collaborative design and simulation, distance learning, and online games. One of the important issues in collaborative applications is floor control wherein the end-users coordinate among themselves to gain exclusive access to the communication channel. An end-user who wins the floor, sends message to all other participating end-users. In this paper, to solve the floor control problem we present an implementation and evaluation of ALOHA and distributed queue dual bus (DQDB) distributed MAC (medium access control) protocols on overlay networks. As an initial step in the implementation of these MAC protocols, we propose an algorithm to construct an efficient communication channel among the Network Service Nodes (NSNs) in the overlay network. We also show that our implementation scheme (first one among decentralized floor control protocols) preserves the causal ordering of messages. We compare the efficiencies of the proposed implementation of floor control protocols using an analytical model that is verified using extensive simulation experiments

Energy-Efficient Transaction Management for Real-Time Mobile Databases in Ad-Hoc Network Environments

In an ad-hoc mobile network architecture, all the mobile hosts (MHs) are connected with each other through a wireless network that has a frequently changing topology. This type of architecture is used in many applications such as battlefields and disaster recovery where it is difficult or not feasible to depend on a static wired communication infrastructure. These applications are usually time-critical where many of their transactions must not only be executed correctly but also within their deadlines. In addition, the MHs in this environment are not connected to unlimited power supplies and may store data that can be shared by other MHs. Existing mobile database transaction management techniques do not consider the ad-hoc network characteristics, real-time constraints and energy limitation. This paper identifies the issues that need to be addressed in this new environment and proposes approaches for solutions.

Multicast Routing with Delay and Delay Variation Constraints for Multimedia Applications

We provide an efficient heuristic algorithm to obtain a multicast network for multimedia applications, given a source and a set of destinations, that is within a specified maximum delay and a specified maximum variation in the delays from a source to the destinations. The time-complexity of our algorithm is O(|E| + nk log (|E|/n) + m 2 k), where n and |E| are the number of nodes and edges in the network, respectively and k is the number of shortest paths computed and m is the number of destinations. We have shown that our algorithm has significant improvements in term of time-complexity compared with the existing algorithms. Our extensive empirical studies indicate that our heuristic uses significantly less run-time in comparison with the best-known heuristics and yet achieves the tightest delay variation for a given end-to-end delay bound.

Implementation of Distributed Floor Control Protocols on Overlay Networks

Collaborative multimedia applications (CMAs) on overlay networks are gaining popularity among users who are geographically dispersed. Examples of these kinds of applications include networked games and collaborative design and simulation. An important challenge in realizing CMAs is obtaining floor control, a problem in which the end-users compete among themselves to gain exclusive access to a shared resource. In this paper, we present deterministic and randomized distributed mechanisms for solving the floor control problem. In particular, we adapt the well-known MAC protocols viz. distributed queue dual bus (DQDB), ALOHA, and carrier sense multiple access (CSMA) as solutions for the floor control problem. Central to our adaptation is an algorithmic methodology that efficiently virtualizes the underlying network connecting the CMA participants so as to enhance the proposed solutions performance. We present analytical and experimental studies on the performance of the proposed floor control protocols that bring out their essential characteristics.

On the heterogeneous postal delivery model for multicasting

The heterogeneous postal delivery model assumes that each intermediate node in the multicasting tree incurs a constant switching time for each message that is sent. We have proposed a new model where we assume a more generalized switching time at intermediate nodes. In our model, a child node v of a parent u has a switching delay vector, where the ith element of the vector indicates the switching delay incurred by u for sending the message to v after sending the message to i - 1 other children of u. Given a multicast tree and switching delay vectors at each non-root node in the tree, we provide an O(n5/2) optimal algorithm that will decide the order in which the internal (non-leaf) nodes have to send the multicast message to its children in order to minimize the maximum end-to-end delay due to multicasting. We also show an important lower bound result that optimal multicast switching delay problem is as hard as min-max matching problem on weighted bi- partite graphs and hence O(n5/2) running time is tight.

Delay Constrained Subtree Homeomorphism Problem with Applications

Virtual world and other collaborative applications are increasingly becoming popular among Internet users. In such applications, users interact with each other through digital entities or avatars. In order to preserve the user experience, it is important that certain Quality of Service (QoS) requirements (e.g., delay and bandwidth) are satisfied by the interactions. These QoS requirements are usually defined by the application designer. When applications with such QoS requirements are being deployed on a network of servers, an appropriate set of servers capable of satisfying the QoS constraints of the interactions must be identified. This identification process is nothing, but the subgraph homeomorphism problem. In this paper, we present polynomial-time solutions for a special case of this problem viz. subtree homeomorphism problem, wherein the guest and the host graphs are both trees. We also discuss generalizations of the subtree homeomorphism problem and present polynomial-time solutions.