Anirudha Sahoo

On Theory of VM Placement: Anomalies in Existing Methodologies and Their Mitigation Using a Novel Vector Based Approach

In this paper, we present the methodologies used in existing literature for Virtual Machine (VM) placement, load balancing and server consolidation in a data center environment. While the methodologies may seem fine on the surface, certain drawbacks and anomalies can be uncovered when they are analyzed deeper. We point out those anomalies and draw backs in the existing literature and explain what are the root causes of such anomalies. Then we propose a novel methodology based on vector arithmetic which not only addresses those anomalies but also leads to some interesting theories and algorithms to tackle the above mentioned three functionalities required in managing resources of data centers. We believe that with a strong mathematical base, our methodology has the potential to become the foundation of future models and algorithms in this research area.

Channel Selection Under Interference Temperature Model in Multi-Hop Cognitive Mesh Networks

A cooperative algorithm based on interference temperature model is proposed for computation of available channels by mesh nodes in a cognitive mesh network. Interference temperature model is used to model occupancy and availability of a channel. Link and end-to-end routing metrics are proposed to select appropriate channels from the computed set of available channels.

An Efficient Call Admission Control for IEEE 802.16 Networks

Scheduling and call admission control (CAC) in IEEE 802.16 system play a vital role in the performance of the system. The 802.16 standard does not specify any scheduling architecture or CAC. Many proposals assume a bandwidth based CAC which only provides bandwidth guarantee, but cannot fulfill delay and jitter requirements. In this paper, we propose a CAC that ensures QoS guarantee in terms of bandwidth, delay and jitter. We also present a novel method of estimating bandwidth requirement of variable bit rate application to increase the resource utilization of the system. We present our simulation result to show the effectiveness of bandwidth estimation and better performance over bandwidth based CAC.

S-OSPF: A Traffic Engineering Solution for OSPF Based Best Effort Networks

Open Shortest Path First (OSPF) is one of the most widely used intra-domain routing protocol. It is well known that OSPF protocol does not provide flexibility in terms of packet forwarding to achieve any network optimization objective. Because of the high cost of network assets and commercial and competitive nature of Internet service provisioning, service providers are interested in performance optimization of their networks. This helps in reducing congestion hotspots and improving resource utilization across the network, which, in turn, results in an increased revenue collection. One way of achieving this is through Traffic Engineering. Currently traffic engineering is mostly done by using MPLS. But legacy networks running OSPF would need to be upgraded to MPLS. To achieve better resource utilization without upgrading OSPF network to MPLS is a challenge. In this paper we present a simple but effective algorithm, called Smart OSPF (S-OSPF) to provide traffic engineering solution in an OSPF based best effort network. We formulate an optimization problem based on the traffic demand to minimize the maximum link utilization in the network. Routing of the traffic demand is achieved using OSPF. We have simulated S-OSPF on real networks of two service providers. Simulation results show that S- OSPF based traffic engineering solution performance very closely follows the optimal solution.

Channel modeling based on interference temperature in underlay cognitive wireless networks

Cognitive radio based dynamic spectrum access network is emerging as a technology to address spectrum scarcity. In this study, we assume that the channel is licensed to some primary (licensed) operator. We consider a sensor network with cognitive radio capability that acts as a secondary (unlicensed) network and uses the channel in underlay mode. The secondary network uses interference temperature model to ensure that the interference to the primary devices remain below a predefined threshold. We use hidden Markov model (HMM) to model the interference temperature dynamics of a primary channel. The HMM is trained using Baum-Welch procedure. The trained HMM is shown to be statistically stable. Secondary nodes use this trained HMM to predict the interference temperature of the channel in future time slots and computes the value of channel availability metric (CAM) for the channel. CAM is used by secondary nodes to select a primary channel for transmission. Results of application of such trained HMMs in channel selection in multi-channel wireless network are presented.

An Energy Efficient MAC in Wireless Sensor Networks to Provide Delay Guarantee

This paper presents RTMAC, a realtime MAC protocol for wireless sensor network that can provide delay guarantee. RTMAC is based on TDMA protocol, but it is carefully designed to overcome the high latency of traditional TDMA protocols. It also conserves energy when a node may not be transmitting or receiving packets. We discuss the details of time slot assignment procedure of RTMAC and then present delay analysis of the protocol. We compare the performance of RTMAC with the well known energy efficient MAC protocol S-MAC using simulation. The simulation results show that RTMAC is better than S-MAC in terms of providing delay guarantee to packets.

DGRAM: A Delay Guaranteed Routing and MAC protocol for wireless sensor networks

This paper presents an integrated MAC and routing protocol called Delay Guaranteed Routing and MAC (DGRAM) for delay-sensitive wireless sensor network (WSN) applications. DGRAM is a TDMA-based protocol designed to provide deterministic delay guarantee in an energy-efficient manner. The design is based on slot reuse to reduce latency of a node in accessing the medium, while ensuring that the medium access is contention-free. The transmission and reception slots of nodes are carefully computed so that data is transported from the source toward the sink while the nodes could sleep at the other times to conserve energy. Thus, routes of data packets are integrated into DGRAM, i.e., there is no need for a separate routing protocol in a DGRAM network. We provide a detailed design of time slot assignment and delay analysis of the protocol. We have simulated DGRAM using ns2 simulator and compared the results with those of FlexiTP, which is another TDMA protocol that claims to provide delay guarantee, and with those of a basic TDMA MAC. Simulation results show that the delay experienced by data packets is always less than the analytical delay bound for which the protocol is designed. Also, the TDMA frame size with DGRAM is always lesser compared to that of FlexiTP, which makes the maximum possible delay much lesser than that of FlexiTP. The average delay experienced by packets and the average total energy spent in the network are much lesser in a network using DGRAM than that using FlexiTP or the basic TDMA MAC.

Stochastic Model Based Opportunistic Channel Access in Dynamic Spectrum Access Networks

We present a stochastic model-based opportunistic channel access and transmission scheme for cognitive radio enabled secondary users for single data channel. We refer to this scheme as Residual Idle Time Distribution based Scheme (RIBS). In this scheme, the SU randomly senses the channel and if the channel is sensed idle, then it uses residual idle time distribution to estimate its transmission duration such that the probability of its interference with PU is below a predefined threshold. We derive analytical formulae for various performance metrics of SU and validate them through simulations. Simulation experiments are conducted for two different scenarios. In the first scenario, we use synthetically generated channel occupancy data due to PU transmissions using two standard distributions (2-phase Erlang and Uniform distribution). In the second scenario, we use data collected by simulating a TDMA-based PU network that runs realistic applications (VoIP and Web browsing). A pair of sender and receiver SU uses RIBS to opportunistically transmit on the channel. Our simulation experiments show that SU can use RIBS to opportunistically transmit on the channel without violating the interference probability constraint. We also list some of the challenges in using RIBS in realistic scenarios, and provide a comprehensive methodology to use RIBS in such scenarios.

A MAC-Aware Energy Efficient Reliable Transport Protocol for Wireless Sensor Networks

In a wireless sensor network (WSN), interesting events are reported to the sink by the sensors in a distributed manner. Applications running at the sink require certain reliability in terms of events per unit time to be able to run satisfactorily. Individual report from sensor nodes is not important, but collective reports from sensor nodes of a region of interest of an application are crucial. Thus, the application event rate can be split across different sensor nodes so as to optimize the usage of scarce resources in WSN such as battery power and memory. In this paper, we propose a transport protocol which provides the desired event reliability to the application, by distributing the load at a sensor among its children based on their residual energies and average MAC layer data rate. The event rate distribution happens in such a way that the application at the sink gets its required event rate and the overall energy consumption of nodes is minimized. This protocol can be used for any MAC protocol as long as the average MAC data rate is known. We take the example of two MAC protocols, Slotted CSMA and Probabilistic TDMA. We derive a method for computing average MAC data rate for these two protocols and then show, using simulations, that our transport protocol performs close to optimal.

Characterizing the exit process of a non-saturated IEEE 802.11 wireless network

In this paper, we consider a non-saturated IEEE 802.11 based wireless network. We use a three-way fixed point to model the node behavior with Bernoulli packet arrivals and determine closed form expressions for the distribution of the time spent between two successful transmissions in an isolated network. The results of the analysis have been verified using extensive simulations in QualNet. The methodology presented in the paper is novel and we believe that the analysis like ours can be used as an approximation to model the behavior of sub-components of a larger mesh or hybrid network.