Vijay Sivaraman

Controlled multimedia wireless link sharing via enhanced class-based queuing with channel-state-dependent packet scheduling

A key problem in transporting multimedia traffic across wireless networks is a controlled sharing of the wireless link by different packet streams. So far this problem has been treated as that of providing support for quality of service in time division multiplexing based medium access control protocols (MAC). Adopting a different perspective to the problem, this paper describes an approach based on extending the class-based queueing (CBQ) based controlled hierarchical link sharing model proposed for the Internet. Our scheme enhances CBQ, which works well in wired links such as point-to-point wires of fixed bandwidth, to also work well with wireless links based on radio channels that are (i) inherently shared on-demand among multiple radios, and (ii) are subject to highly dynamic bandwidth variations due to spatially and temporally varying fading with accompanying burst errors. The proposed scheme is based on combining a modified version of CBQ with channel-state dependent packet scheduling.

Survey on network mobility support

Providing unperturbed Internet connectivity to mobile hosts has been studied in the IETF for some years now, and protocols such as Mobile IP and Mobile IPv6 have been developed. We are now witnessing the emergence of mobile networks, namely a set of hosts that move collectively as a unit, such as on ships and aircrafts. The protocols for mobility support therefore need to be extended from supporting an individual mobile device to supporting an entire mobile network. In this paper we examine the state-of-the-art in network mobility support. We first motivate the problem by considering typical network mobility scenarios and identify the characteristics that require new solutions. We then study the design requirements of the protocols that support network mobility. Thereafter, we review some of the current approaches for network mobility support, and discuss their strengths and weaknesses in addressing the design requirements. We conclude by identifying some open research issues in the realization of mobile networks.

Transmission Power Control in Body Area Sensor Networks for Healthcare Monitoring

This paper investigates the opportunities and challenges in the use of dynamic radio transmit power control for prolonging the lifetime of body-wearable sensor devices used in continuous health monitoring. We first present extensive empirical evidence that the wireless link quality can change rapidly in body area networks, and a fixed transmit power results in either wasted energy (when the link is good) or low reliability (when the link is bad). We quantify the potential gains of dynamic power control in body-worn devices by benchmarking off-line the energy savings achievable for a given level of reliability.We then propose a class of schemes feasible for practical implementation that adapt transmit power in real-time based on feedback information from the receiver. We profile their performance against the offline benchmark, and provide guidelines on how the parameters can be tuned to achieve the desired trade-off between energy savings and reliability within the chosen operating environment. Finally, we implement and profile our scheme on a MicaZ mote based platform, and also report preliminary results from the ultra-low-power integrated healthcare monitoring platform we are developing at Toumaz Technology.

Packet scheduling in broadcast WDM networks with arbitrary transceiver tuning latencies

We consider the problem of scheduling packet transmissions in a broadcast, single-hop wavelength-division multiplexing (WDM) network, with tunability provided only at one end. Our objective is to design schedules of minimum length to satisfy a set of traffic requirements given in the form of a demand matrix. We address a fairly general version of the problem as we allow arbitrary traffic demands and arbitrary transmitter tuning latencies. The contribution of our work is twofold, First we define a special class of schedules which permit an intuitive formulation of the scheduling problem. Based on this formulation we present algorithms which construct schedules of length equal to the lower bound provided that the traffic requirements satisfy certain optimality conditions. We also develop heuristics which, in the general case, give schedules of length equal or very close to the lower bound. Secondly, we identify two distinct regions of network operation. The first region is such that the schedule length is determined by the tuning requirements of transmitters; when the network operates within the second region however, the length of the schedule is determined by the traffic demands, not the tuning latency. The point at which the network switches between the two regions is identified in terms of system parameters such as the number of nodes and channels and the tuning latency. Accordingly, we show that it is possible to appropriately dimension the network to minimize the effects of even large values of the tuning latency.

Perspectives on router buffer sizing: recent results and open problems

The past few years have witnessed a lot of debate on how large Internet router buffers should be. The widely believed rule-of-thumb used by router manufacturers today mandates a buffer size equal to the delay-bandwidth product. This rule was first challenged by researchers in 2004 who argued that if there are a large number of long-lived TCP connections flowing through a router, then the buffer size needed is equal to the delay-bandwidth product divided by the square root of the number of long-lived TCP flows. The publication of this result has since reinvigorated interest in the buffer sizing problem with numerous other papers exploring this topic in further detail - ranging from papers questioning the applicability of this result to proposing alternate schemes to developing new congestion control algorithms, etc. This paper provides a synopsis of the recently proposed buffer sizing strategies and broadly classifies them according to their desired objective: link utilisation, and per-flow performance. We discuss the pros and cons of these different approaches. These prior works study buffer sizing purely in the context of TCP. Subsequently, we present arguments that take into account both real-time and TCP traffic. We also report on the performance studies of various high-speed TCP variants and experimental results for networks with limited buffers. We conclude this paper by outlining some interesting avenues for further research.

Profiling per-packet and per-byte energy consumption in the NetFPGA Gigabit router

Improving energy efficiency of Internet equipment is becoming an increasingly important research topic, motivated by the need to reduce energy costs (and Carbon footprint) for Internet Service Providers, as well as increase power density to achieve more switching capacity per-rack. While recent research has profiled the power consumption of commercial routing equipment, these profiles are coarse-grained (i.e., at the granularity of per line-card or per port), and moreover such platforms are inflexible for experimentation with new energy-saving mechanisms. In this paper we therefore consider the NetFPGA platform, which is becoming an increasingly popular routing platform for networking research due to its versatility and low-cost. Using a precise hardware-based traffic generator and high-fidelity energy probe, we conduct several experiments that allow us to decompose the energy consumption of the NetFPGA routing card into fine-grained per-packet and per-byte components with reasonable accuracy. Our quantification of energy consumption on this platform opens the doors for estimating network-wide energy footprints at the granularity of traffic sessions and applications (e.g., due to TCP file transfers), and provides a benchmark against which energy improvements arising from new architectures and protocols can be evaluated.

Providing end-to-end statistical delay guarantees with earliest deadline first scheduling and per-hop traffic shaping

This paper develops a framework for statistically guaranteeing end-to-end delay bounds to leaky-bucket-constrained flows transporting real-time traffic in a network of switches using earliest deadline first (EDF) packet scheduling and per-hop traffic shaping. We first analyze the delay-bound violation probabilities at an isolated EDF scheduler fed by fluid source processes generating extremal dual-leaky-bucket-regulated traffic. We compute a close upper bound by applying the Benes approach to an equivalent hypothetical system derived from the real one. We then extend the analysis to the end-to-end scenario in the presence of traffic re-shaping at each node in the network. We compare the analytical results with simulations, and show that the match is very close. We also investigate the advantages of smoothing the traffic at the ingress to the network, and propose a simple choice of smoothing parameters, which perform very well. Using realistic traffic parameters, we compare the schedulable region of our statistical framework with that of the corresponding deterministic framework, and demonstrate that the statistical framework allows tremendous improvements in network utilization, even for very low delay-violation probabilities. The framework developed in this paper is therefore highly useful in practical packet networks to provide quality of service to real-time applications in the form of statistical, rather than deterministic, end-to-end delay bounds.

End-to-end statistical delay service under GPS and EDF scheduling: a comparison study

Generalized processor sharing (GPS) has gained much popularity as a simple and effective scheduling mechanism for the provisioning of quality of service (QoS) in emerging high-speed networks. For supporting deterministic end-to-end delay guarantees, GPS is known to be sub-optimal in comparison to the earliest deadline first (EDF) scheduling discipline; nevertheless it is often prefered over EDF due to its simplicity. In this paper, using analytical frameworks developed in the literature, we reassess the merits of GPS as compared to EDF in the setting of statistical delay service. Our contributions are threefold. The statistical frameworks in the literature enable the aggregate losses (i.e., delay bound violations) at an EDF scheduler to be estimated-our first contribution, therefore, is to develop a mechanism that allows the aggregate losses to translate to per-flow guarantees. This is achieved by means of a simple packet discard scheme that drops packets fairly then delay violations are imminent at the EDF scheduler. The discard mechanism has a constant complexity and is feasible for implementation in current packet switches. The ability to derive the per-flow guarantees from the aggregate allows a direct comparison between EDF and GPS-our next contribution, therefore, is to show for various traffic mixes with given per-flow loss constraints that EDF offers consistently larger schedulable regions than GPS, both in the single-hop and multi-hop setting. As our final contribution, we argue that the use of GPS for statistical delay support is inherently problematic. We demonstrate that achieving the maximal schedulable regions under GPS could necessitate dynamic resynchronization of the GPS weights, an operation considered infeasible for practical implementation.

Achieving high utilization in guaranteed services networks using early-deadline-first scheduling

Among packet scheduling disciplines for providing end-to-end quality-of-service (QoS) guarantees to different applications, two classes of algorithms have received particular attention: those based on generalized processor sharing (GPS) and those based on earliest-deadline first (EDF) scheduling. The powerful properties of GPS-based schemes translate easily into simple call admission control (CAC) procedures. The intense research on GPS has also resulted in very efficient implementation techniques, which have made the cost of these schedulers very affordable. The EDF discipline, in conjunction with per-node traffic shaping [which we refer to as rate-controlled EDF (RC-EDF)] has also been proposed for end-to-end QoS provisioning. However, an appropriate framework for CAC with RC-EDF has not been developed, nor the possible advantages of using RC-EDF in place of GPS have been properly characterized. Furthermore, the implementation complexity of an RC-EDF server is potentially very high, and no technique to reduce costs has been proposed. In this paper, we first formulate an end-to-end CAC framework for RC-EDF that can be implemented in practice. Then, using this framework, we numerically compare the schedulable regions of RC-EDF and GPS and show that, when the traffic mix in the network consists of connections with both stringent and loose delay requirements, RC-EDF can substantially outperform GPS in the number of admitted connections, and can thus achieve much higher network utilization. Finally, we propose a technique to substantially reduce the implementation complexity of a RC-EDF server.

A Survey of Securing Networks Using Software Defined Networking

Software Defined Networking (SDN) is rapidly emerging as a new paradigm for managing and controlling the operation of networks ranging from the data center to the core, enterprise, and home. The logical centralization of network intelligence presents exciting challenges and opportunities to enhance security in such networks, including new ways to prevent, detect, and react to threats, as well as innovative security services and applications that are built upon SDN capabilities. In this paper, we undertake a comprehensive survey of recent works that apply SDN to security, and identify promising future directions that can be addressed by such research.