A Framework for Service Differentiation and Optimization in Multi-hop Wireless Networks

In resource-constrained networks such as multi-hop wireless networks (MHWNs), service differentiation algorithms designed to address end users' interests (e.g. user satisfaction, QoS, etc.) should also consider efficient utilization of the scarce network resources in order to maximize the network's interests (e.g. revenue). For this very reason, service differentiation in MHWNs is quite different from the wired network scenario. We propose a service differentiation tool called the ``Investment Function'', which essentially captures the network's cumulative resource investment in a given packet at a given time. This investment value can be used by the network algorithm to implement specific service differentiation principles. As proof-of-concept, we use the investment function to improve fairness among simultaneous flows that traverse varying number of hops in a MHWN (multihop flow fairness). However, to attain the optimal value of a specific service differentiation objective, optimal service differentiation and investment function parameters may need to be computed. The optimal parameters can be computed by casting the service differentiation problem as a network flow problem in MHWNs, with the goal of optimizing the service differentiation objective. The capacity constraints for these problems require knowledge of the adjacent-node interference values, and constructing these constraints could be very expensive based on the transmission scheduling scheme used. As a result, even formulating the optimization problem may take unacceptable computational effort or memory or both. Under optimal scheduling, the adjacent node interference values (and thus the capacity constraints) are not only very expensive to compute, but also cannot be expressed in polynomial form. Therefore, existing optimization techniques cannot be directly applied to solve optimization problems in MHWNs. To develop an efficient optimization framework, we first model the MHWN as a Unit Disk Graph (UDG). The optimal transmission schedule in the MHWN is related to the chromatic number of the UDG, which is very expensive to compute. However, the clique number, which is a lower bound on the chromatic number, can be computed in polynomial time in UDGs. Through an empirical study, we obtain tighter bounds on the ratio of the chromatic number to clique number in UDGs, which enables us to leverage existing polynomial time clique-discovery algorithms to compute very close approximations to the chromatic number value. This approximation not only allows us to quickly formulate the capacity constraints in polynomial form, but also allows us to significantly deviate from the traditional approach of discovering all or most of the constraints \textit{a priori}; instead, we can discover the constraints as needed. We have integrated this approach of constraint-discovery into an active-set optimization algorithm (Gradient Projection method) to solve network flow problems in multi-hop wireless networks. Our results show significant memory and computational savings when compared to existing methods

Clique Number Vs. Chromatic Number in Wireless Interference Graphs: Simulation Results

Abstract- Interference due to transmissions by adjacent nodes in a multi-hop wireless network can be modeled using a Unit Disc Graph (UDG). We investigate the reliability associated with using the clique number instead of the chromatic number of the UDG while computing the interference. In our extensive simulations with UDGs of random networks, we observed that the clique number and the chromatic number values were typically very close to one another and the maximum deviation was much less than the theoretical bounds. This implies very high reliability in the proposed approximation. Index Terms – wireless interference, clique number, chromatic number, unit disk graph, imperfection ratio I

Terminologies 4

This technical report is a compilation of the results of various simulations conducted using the KU-PNNI simulator during the academic year 2001 -- 2002. Analyses of the results are primarily based on evidence collected during the course of the simulation, in the absence of which the analysis is based on a plausible hypothesis drawn after extensive discussion. Pictorial representations of the test topologies and plots of results are provided wherever deemed necessary. For more information on the KU-PNNI simulator, refer to the KU-PNNI user's manual [1

Surviving failures in bandwidthconstrained datacenters

Abstract-Datacenter networks have been designed to tolerate failures of network equipment and provide sufficient bandwidth. In practice, however, failures and maintenance of networking and power equipment often make tens to thousands of servers unavailable, and network congestion can increase service latency. Unfortunately, there exists an inherent tradeoff between achieving high fault tolerance and reducing bandwidth usage in network core; spreading servers across fault domains improves fault tolerance, but requires additional bandwidth, while deploying servers together reduces bandwidth usage, but also decreases fault tolerance. We present a detailed analysis of a large-scale Web application and its communication patterns. Based on that, we propose and evaluate a novel optimization framework that achieves both high fault tolerance and significantly reduces bandwidth usage in the network core by exploiting the skewness in the observed communication patterns

Organ Transplantation, Pros, Cons, and illustrations: A Basic Awareness to the Public

Solid-organ transplantation saves the lives of patients affected by end-stage organ failure and enhances the quality of life. It has been developed in the last two decades and provides amazing results for children and young people and increases the growing number of elderly transplant patients with organ transplantation. Use of corticosteroids, vaccines, and other drugs to avoid infection in diseased patients. Several approaches have been developed to prolong organ obtainability, including living donor liver transplantation, split liver transplantation, and application of expanded criteria for donors and donation after circulatory death grafts. Unprincipled practices in many countries are due to the availability of organs. Organ transplantation requires screening and comparative contraindications in the recipient. The authors want to give a general awareness to the public, which is essential to know for donating and receiving organs from others