Network virtualization and overlay networks have emerged as powerful tools for improving the flexibility of the Internet. Overlays are used to provide a wide range of useful services in today's networking environment, and they are also viewed as important building blocks for an agile and evolvable future Internet. Regardless of the specific service it provides, an overlay needs assistance in several areas in order to perform properly throughout its existence. This dissertation focuses on the mechanisms underlying the provision of auxiliary support services that perform control and management functions for overlays, such as overlay assignment, resource allocation, overlay monitoring and diagnosis. The priorities and objectives in the design of such mechanisms depend on network conditions and the virtualization environment. We identify opportunities for improvements that can help provide auxiliary services more effectively at different overlay life stages and under varying assumptions. The contributions of this dissertation are the following: 1. An overlay assignment algorithm designed to improve an overlay's diagnosability, which is defined as its property to allow accurate and low-cost fault diagnosis. The main idea is to increase meaningful sharing between overlay links in a controlled manner in order to help localize faults correctly with less effort. 2. A novel definition of bandwidth allocation fairness in the presence of multiple resource sharing overlays, and a routing optimization technique to improve fairness and the satisfaction of overlays. Evaluation analyzes the characteristics of different fair allocation algorithms, and suggests that eliminating bottlenecks via custom routing can be an effective way to improve fairness. 3. An optimization solution to minimize the total cost of monitoring an overlay by determining the optimal mix of overlay and native links to monitor, and an analysis of the effect of topological properties on monitoring cost and the composition of the optimal mix of monitored links. We call our approach multi-layer monitoring and show that it is a flexible approach producing minimal-cost solutions with low errors. 4. A study of virtual network embedding in software defined networks (SDNs), identifying the challenges and opportunities for embedding in the SDN environment, and presenting two VN embedding techniques and their evaluation. One objective is to balance the stress on substrate components, and the other is to minimize the delays between VN controllers and switches. Each technique optimizes embedding for one objective while keeping the other within bounds.

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Communication and networking are vast areas which are developing rapidly. It is very important to know in detail how the system works, how it can be enhanced to meet today's requirement, how to implement the appropriate techniques to obtain desired results etc. To explain all of the above, simulation techniques were adopted. Simulation plays an important role in developming new designs and modifying existing systems to make them more feasible and efficient.Protocols are the back bones of the communication systems and play a major role in data transfer. The review of literature provides an explanation of ISO/OSI models, layered approach and concepts of simulation. The simulation was carried out to explain the concepts of error detection, error correction and flow control in Data Link layer. Ada was used to develop the software, because of its concurrent processing tools called tasks. Also state-of-the-art utilities like Vax/Vms Screen Management System, File Definition Language, and Debugger were us ed in the program development. / Department of Computer Science

This thesis compares an online church with a local physical church in terms of communication dimensions of the community, communication dimensions of sacramental practice, and communication dimensions of faith in general. In a local physical church, these have been traditionally conceived, defined, and profoundly understood in phenomenal or physical terms. In this, the objects of faith and the related rituals deal with the “real” and give even the transcendent physical and actual meaning. However, in an online environment, what was previously physical has become virtual, thus causing the transcendent to be virtualized as well. As such, two guiding questions for this thesis are: 1) Given the virtual nature of the Internet, do the beliefs that a church advocates seem to be or become less real or phenomenal when a church predominantly employs religious practices online; and, 2) Given the power and range of responses that individuals can have when responding to Internet content, do the beliefs that a church advocates become more ideocentric and emotional for its online users? Given the tremendous variations that are employed in religious groups, these two questions will naturally generate more heuristic rather than universal findings, as the title recognizes. LifeChurch.tv has been chosen as the subject for this heuristic investigation due to its manifestation in both an online church and in local physical counterparts. Each is examined through the LifeChurch.tv website using a method of ethnographic research, combined with a longitudinal study, and the resulting findings are interpreted through cluster criticism. A less grounded and more individualistic experience was found in the rhetoric surrounding the online church. / Literature review & theoretical background -- Methods for analysis -- A cluster analysis of a local physical church and online church website -- Major findings, limitations and suggestions for future research. / Department of Telecommunications

In this dissertation, we discuss the design of a reconfigurable, unified HMAC-hash unit for IPSec authentication. The proposed unit is reconfigurable at runtime to enable implementing any of six standard algorithms: MD5, SHA-1, RIPEMD-160. HMAC-MD5. HMAC-SHA-1, and HMAC-RIPEMD-160. The designed unit can be used for IPSec or any other security application that uses hash functions, such as digital signature. We applied speedup techniques, such as pipelining and parallelism, to enhance the design of the HMAC-hash unit. We also proposed a key reuse technique to improve the HMAC through-put. We used an emerging system design methodology in designing the HNLAC-hash unit. This methodology uses a high level language, Handel-C, to implement the designed unit and directly map it to FPGA platforms. We used the available constructs of Handel-C to conduct a design space exploration of the HMAC-hash unit. The performance of the designed unit was analyzed and compared to performance reported in previous work. To our knowledge, this work is the first in the literature that integrates six standard hash algorithms in one unified, reconfigurable unit. It is also the first in the literature that implements HMAC-RIPEMD-160 on FPGA. The work reported in this dissertation is the first to integrate HMAC with three hash functions. The achieved throughput is 173.69 Mbps for MD5 and 139.38 Mbps for each of SHA-I and RIPEMD-160. Compared to results reported in previous work, our unit achieves better throughput than those integrating three or more hash functions and a comparable throughput to those integrating two hash functions. We achieved better maximum frequency, which is 44.1 MHz. than all other work. We achieved comparable results to those integrating HMAC with some hash functions. The area utilization of the designed unit is less than 33% of the available logic on the FPGA chip we used. Thus, the designed unit can fit on a single FPGA chip as an SoC.

As Multi-Protocol Label Switched (MPLS) networks increase in usage and size, the number of traffic engineered tunnels or Label Switched Paths (LSPs) which must be established has an impact on network state maintenance, administration and scalability. The ability to signal and meet Quality-of-Service (QoS) requirements in such networks has been addressed through the addition of Differentiated Services (Diff-Serv) mappings and other traffic engineering mechanisms. However, for the purpose of path computation, route advertisements, signaling and admission control, multiple traffic classes carried together are still treated as a single class. This work explores extensions to MPLS which allow for the accommodation of up to eight distinct traffic classes per label switched path. Through an examination of simulation results. a comparison between existing methods and the proposed additions is made that shows scenarios in which such traffic class aggregation or "bundling" provides a significant reduction in the number of paths which must be maintained in the network.

Despite the persistent change and growth that characterizes the Internet, the Transmission Control Protocol (TCP) still dominates at the transport layer, carrying more than 90\% of the global traffic. Despite its astonishing success, it has been observed that TCP can cause poor end-to-end performance, especially for large transfers and in network paths with high bandwidth-delay product. In this thesis, we focus on mechanisms that can address key problems in TCP performance, without any modification in the protocol itself. This evolutionary approach is important in practice, as the deployment of clean-slate transport protocols in the Internet has been proved to be extremely difficult. Specifically, we identify a number of TCP-related problems that can cause poor end-to-end performance. These problems include poorly dimensioned socket buffer sizes at the end-hosts, suboptimal buffer sizing at routers and switches, and congestion unresponsive TCP traffic aggregates. We propose solutions that can address these issues, without any modification to TCP. <br> <br> In network paths with significant available bandwidth, increasing the TCP window till observing loss can result in much lower throughput than the path's available bandwidth. We show that changes in TCP are {em not required} to utilize all the available bandwidth, and propose the application-layer SOcket Buffer Auto-Sizing (SOBAS) mechanism to achieve this goal. SOBAS relies on run-time estimation of the round trip time (RTT) and receive rate, and limits its socket buffer size when the receive rate approaches the path's available bandwidth. In a congested network, SOBAS does not limit its socket buffer size. Our experiment results show that SOBAS improves TCP throughput in uncongested network without hurting TCP performance in congested networks. <br> <br> Improper router buffer sizing can also result in poor TCP throughput. Previous research in router buffer sizing focused on network performance metrics such as link utilization or loss rate. Instead, we focus on the impact of buffer sizing on end-to-end TCP performance. We find that the router buffer size that optimizes TCP throughput is largely determined by the link's output to input capacity ratio. If that ratio is larger than one, the loss rate drops exponentially with the buffer size and the optimal buffer size is close to zero. Otherwise, if the output to input capacity ratio is lower than one, the loss rate follows a power-law reduction with the buffer size and significant buffering is needed. The amount of buffering required in this case depends on whether most flows end in the slow-start phase or in the congestion avoidance phase. <br> <br> TCP throughput also depends on whether the cross-traffic reduces its send rate upon congestion. We define this cross-traffic property as {em congestion responsiveness}. Since the majority of Internet traffic uses TCP, which reduces its send rate upon congestion, an aggregate of many TCP flows is believed to be congestion responsive. Here, we show that the congestion responsiveness of aggregate traffic also depends on the flow arrival process. If the flow arrival process follows an open-loop model, then even if the traffic consists exclusively of TCP transfers, the aggregate traffic can still be unresponsive to congestion. TCP flows that arrive in the network in a closed-loop manner are always congestion responsive, on the other hand. We also propose a scheme to estimate the fraction of traffic that follows the closed-loop model in a given link, and give practical guidelines to increase that fraction with simple application-layer modifications.

<p>SIP is receiving much attention these days and it seems to be the most promising candidate as a signaling protocol for the current and future IP telephony services. Realizing this, there is the obvious need to provide a certain level of quality comparable to the traditional telephone service signalling system. Thus, we identified the major costs of SIP, which were found to be delay and security. This thesis discusses the costs of SIP, the solutions for the major costs, and the development of a low cost SIP application. The literature review of the components used to develop such a service is discussed, the networks in which the SIP is used are outlined, and some SIP applications and services previously designed are discussed. A simulation environment is then designed and implemented for the instant messaging service for wireless devices. This environment simulates the average delay in LAN and WLAN in different scenarios, to analyze in which scenario the system has the lowest costs and delay constraints.</p>