https://etd.iisc.ac.in/handle/2005/32 2026-04-23T19:44:50Z 2026-04-23T19:44:50Z Sreedhar, Y https://etd.iisc.ac.in/handle/2005/7105 2025-11-18T11:54:42Z

A protocol for the Bi-directional connectivity of peers in the presence of heterogeneous internet address space Sreedhar, Y The number of hosts connecting to the Internet is growing day by day, and the available statistics show that this growth is exponential. This growth has made IP address a scarce resource. IPv6 is proposed as a long term solution to the problem of depletion of IP address space. IPv6 has many advantages over IPv4, and is carefully designed to serve the future requirements. But the migration from IPv4 to IPv6 can’t be done over night, because it requires extensive modifications to the existing infrastructure. It will take around 15 to 20 years to deploy IPv6 fully. Some temporary solutions to solve the problem have been proposed in the literature. One such temporary solution is NAT (Network Address Translator). Network Address Translator (NAT) gateway provides a way of utilizing the available IP addresses effectively. NAPT or Network Address Port Translator is one popular flavor of NAT gateway which uses one IP address and multiplexes many hosts to connect to the Internet. On the Internet every connection is identified by four parameters. They are source IP address, source port number, destination IP address and destination port number. In each and every out-going packet the NAPT changes source IP address to its own IP address, but the source port is changed to a unique value that is used to associate incoming packets with the private network address. NAPT maintains full outbound connectivity and denies the internal hosts the ability to receive unsolicited inbound connections. That is, connection initiation can be done only from the internal host. The host outside the NAT can’t initiate a connection to the host behind the NAT. This denial of inbound connections is to provide security to the internal hosts. The NAPT is fully transparent to the end-users, since the source ports in the IP packet headers are translated on the fly. In the normal client server architecture, the lack of inbound connectivity is fine because all servers are located in the public domain. But the current world is moving towards the peer to peer networking. In peer to peer networking, the distinction between a client and a server vanishes and, every host acts as both client and server. This is to exploit the databases distributed among the peers. Under these circumstances every host demands inbound connectivity. The major application of the peer to peer networking is in file sharing. This thesis proposes a novel technique to solve the problem of lack of inbound connectivity of NAT, by modifying the peer to peer file sharing protocol, while retaining the advantage of NAT in utilizing the IP address space effectively. In the proposed method all inbound IP packets are sent to the NAT gateway, and prior to that, NAT gateway is instructed, as to which private IP host these packets should go inside its own domain. For this to happen the initiator should know both the IP addresses of the NAT and the responder which is behind the NAT. This is done by modifying the directory service at the central host, which contains the details about the location of files. The modifications needed at the NAT gateway and to the peer to peer networking protocol to solve the lack of inbound connectivity problem of NAT, are presented in this thesis. Organization of Thesis The thesis is organized in 5 chapters as follows: Chapter I gives an elaborate account of present status of the Internet. The problem of scarcity of IPv4 address space is discussed. The temporary and permanent solutions to solve this problem is discussed. The problem of lack of inbound connectivity of NAT, which gets more attention in peer to peer networking is stated. Here the scope of the work is defined. Chapter II deals with a survey of the existing solutions to alleviate the lack of inbound connectivity problem of the NAT. The positive and negative aspects associated with each of these solutions are discussed. Chapter III explains the proposed solution to solve the lack of inbound connectivity on the NAT. Chapter IV deals with the implementation details of the proposed solution. Since the proposed solution is a protocol, all the packet formations used and all fields are explained in this chapter. Chapter V summarizes the contributions made by the thesis. Suggestions for future work is also included in this chapter.

Tellakula, Ashok Kumar https://etd.iisc.ac.in/handle/2005/595 2020-10-06T10:49:32Z 2009-08-19T06:26:54Z

Acoustic Source Localization Using Time Delay Estimation Tellakula, Ashok Kumar The angular location of an acoustic source can be estimated by measuring an acoustic direction of incidence based solely on the noise produced by the source. Methods for determining the direction of incidence based on sound intensity, the phase of cross-spectral functions, and cross-correlation functions are available. In this current work, we implement Dominant Frequency SElection (DFSE) algorithm. Direction of arrival (DOA) estimation usingmicrophone arrays is to use the phase information present in signals from microphones that are spatially separated. DFSE uses the phase difference between the Fourier transformedsignals to estimate the direction ofarrival (DOA)and is implemented using a three-element ’L’ shaped microphone array, linear microphone array, and planar 16-microphone array. This method is based on simply locating the maximum amplitude from each of the Fourier transformed signals and thereby deriving the source location by solving the set of non-linear least squares equations. For any pair of microphones, the surface on whichthe time difference ofarrival (TDOA) is constant is a hyperboloidoftwo sheets. Acoustic source localization algorithms typically exploit this fact by grouping all microphones into pairs, estimating the TDOA of each pair, then finding the point where all associated hyperboloids most nearly intersect. We make use of both closed-form solutions and iterative techniques to solve for the source location.Acoustic source positioned in 2-dimensional plane and 3-dimensional space have been successfully located.

2009-08-19T06:26:54Z George, Cijo https://etd.iisc.ac.in/handle/2005/3240 2019-09-13T11:21:56Z 2018-03-07T00:00:00Z

Adaptive Fault Tolerance Strategies for Large Scale Systems George, Cijo Exascale systems of the future are predicted to have mean time between node failures (MTBF) of less than one hour. At such low MTBF, the number of processors available for execution of a long running application can widely vary throughout the execution of the application. Employing traditional fault tolerance strategies like periodic checkpointing in these highly dynamic environments may not be effective because of the high number of application failures, resulting in large amount of work lost due to rollbacks apart from the increased recovery overheads. In this context, it is highly necessary to have fault tolerance strategies that can adapt to the changing node availability and also help avoid significant number of application failures. In this thesis, we present two adaptive fault tolerance strategies that make use of node failure pre-diction mechanisms to provide proactive fault tolerance for long running parallel applications on large scale systems. The first part of the thesis deals with an adaptive fault tolerance strategy for malleable applications. We present ADFT, an adaptive fault tolerance framework for long running malleable applications to maximize application performance in the presence of failures. We first develop cost models that consider different factors like accuracy of node failure predictions and application scalability, for evaluating the benefits of various fault tolerance actions including check-pointing, live-migration and rescheduling. Our adaptive framework then uses the cost models to make runtime decisions for dynamically selecting the fault tolerance actions at different points of application execution to minimize application failures and maximize performance. Simulations with real and synthetic failure traces show that our approach outperforms existing fault tolerance mechanisms for malleable applications yielding up to 23% improvement in work done by the application in the presence of failures, and is effective even for petascale and exascale systems. In the second part of the thesis, we present a fault tolerance strategy using adaptive process replication that can provide fault tolerance for applications using partial replication of a set of application processes. This fault tolerance framework adaptively changes the set of replicated processes (replicated set) periodically based on node failure predictions to avoid application failures. We have developed an MPI prototype implementation, PAREP-MPI that allows dynamically changing the replicated set of processes for MPI applications. Experiments with real scientific applications on real systems have shown that the overhead of PAREP-MPI is minimal. We have shown using simulations with real and synthetic failure traces that our strategy involving adaptive process replication significantly outperforms existing mechanisms providing up to 20% improvement in application efficiency even for exascale systems. Significant observations are also made which can drive future research efforts in fault tolerance for large and very large scale systems.

2018-03-07T00:00:00Z Nainwal, Kalash Chandra https://etd.iisc.ac.in/handle/2005/1397 2025-12-03T11:26:41Z 2011-09-06T00:00:00Z

Adaptive Grid Meta Scheduling - A QoS Perspective Nainwal, Kalash Chandra

2011-09-06T00:00:00Z