Ioannis Lambadaris

An overview of pricing concepts for broadband IP networks

In this article we provide an overview of pricing concepts for broadband multiservice networks. We review the notions of flat pricing, priority pricing, Paris-Metro pricing, smart-market pricing, responsive pricing, expected capacity pricing, edge pricing, and effective bandwidth pricing. We use numerous evaluation criteria, including network, economic, and social efficiency, as well as their suitability in using pricing as a means for congestion control. Some of the schemes are based on best-effort networks, and are thus unable to provide the user with quality of service (QoS) guarantees. Others build on networks with connection admission control functions and are thus able to provide individual QoS guarantees. We particularly investigate the relevant time frame over which pricing schemes are assumed to operate. The majority of the schemes work on short time frames (on the order of minutes), which makes them applicable to use pricing as an additional means for controlling congestion. We also consider technical aspects such as compliance with existing networking technologies or computational overheads associated with billing and accounting.

Modeling and simulation of self-similar variable bit rate compressed video: a unified approach

Variable bit rate (VBR) compressed video is expected to become one of the major loading factors in high-speed packet networks such as ATM-based B-ISDN. However, recent measurements based on long empirical traces (complete movies) revealed that VBR video traffic possesses self-similar (or fractal) characteristics, meaning that the dependence in the traffic stream lasts much longer than traditional models can capture.In this paper, we present a unified approach which, in addition to accurately modeling the marginal distribution of empirical video records, also models directly both the short and the long-term empirical autocorrelation structures. We also present simulation results using synthetic data and compare with results based on empirical video traces.Furthermore, we extend the application of efficient estimation techniques based on importance sampling that we had used before only for simple fractal processes. We use importance sampling techniques to efficiently estimate low probabilities of packet losses that occur when a multiplexer is fed with synthetic traffic from our self-similar VBR video model.

On minimizing the sum ofensor movements for barrier coverage of a line segment

A set of sensors establishes barrier coverage of a given line segment if every point of the segment is within the sensing range of a sensor. Given a line segment I, n mobile sensors in arbitrary initial positions on the line (not necessarily inside I) and the sensing ranges of the sensors, we are interested in finding final positions of sensors which establish a barrier coverage of I so that the sum of the distances traveled by all sensors from initial to final positions is minimized. It is shown that the problem is NP complete even to approximate up to constant factor when the sensors may have different sensing ranges. When the sensors have an identical sensing range we give several efficient algorithms to calculate the final destinations so that the sensors either establish a barrier coverage or maximize the coverage of the segment if complete coverage is not feasible while at the same time the sum of the distances traveled by all sensors is minimized. Some open problems are also mentioned.

Fast simulation for self-similar traffic in ATM networks

Self-similar (or fractal) stochastic processes were proposed as more accurate models of certain categories of traffic (e.g., Ethernet traffic, variable-bit-rate video) which will be transported in ATM networks. Existing analytical results for the tail distribution of the waiting time in a single server queue based on fractional Gaussian noise and large deviation theory, are valid under a steady-state regime and for an asymptotically large buffer size. However, the predicted performance based on steady-state regimes may be overly pessimistic for practical applications. Theoretical approaches used to obtain the transient queueing behavior and queueing distributions for a small buffer size become quickly intractable. The approach we followed was based on fast simulation techniques for the study of certain rare events such as cell losses with very small probability of occurrence. Our simulation experiments provide an insight on the transient behavior that is not possible to predict using current analytical results. Finally they show good agreement with existing results when approaching steady-state.

Performance analysis of first-fit wavelength assignment algorithm in optical networks

This paper proposes a new analytical technique for the performance analysis of all optical networks which use the first-fit algorithm for wavelength assignment. We analyze the wavelength usage on the links to calculate the blocking probability of a source destination pair, taking into account wavelength correlation and load correlation between links. Our model is accurate even in a system with large number of wavelengths.

Source routed forwarding with software defined control, considerations and implications

The research introduced in this paper focuses on controller scalability and performance issues in Software-Defined Networks (SDNs), and discusses a new routing scheme that leverages a variation of Source Routing for use in OpenFlow-based networks. The research aims to reduce the state needed to be distributed to the network devices by the controller(s) in SDNs, and in return improve the scale, convergence time, fault tolerance and cost of such network architectures.

A survey of congestion control schemes for multicast video applications

Congestion control for IP multicast on the Internet has been one of the main issues that challenge a rapid deployment of IP multicast. In this article, we survey and discuss the most important congestion control schemes for multicast video applications on the Internet. We start with a discussion of the different elements of a multicast congestion control architecture. A congestion control scheme for multicast video possesses specific requirements for these elements. These requirements are discussed, along with the evaluation criteria for the performance of multicast video. We categorize the schemes we present into end-to-end schemes and router-supported schemes. We start with the end-to-end category and discuss several examples of both single-rate multicast applications and layered multicast applications. For the router-supported category, we first present single-rate schemes that utilize filtering of multicast packets by the routers. Next we discuss receiver-based layered schemes that rely on routers group/flow control of multicast sessions. We evaluate a number of schemes that belong to each of the two categories.

Efficient fractional Gaussian noise generation using the spatial renewal process

An efficient and easy technique to generate fractional Gaussian noise traffic based on the spatial renewal process is developed and demonstrated. The synthetically generated trace reproduces the desired marginal, autocorrelation and Hurst parameters well. The model is particularly suitable for use in the discrete-event simulation of queueing systems involving VBR compressed video and aggregated LAN traffic.

HMM delay prediction technique for VoIP

This paper proposes a new algorithm for predicting audio packet playout delay for voice conferencing applications that use silence suppression. The proposed algorithm uses a hidden Markov model (HMM) to predict the playout delay. Several existing algorithms are reviewed to show that the HMM technique is based on a combination of various desirable features of other algorithms. Voice over Internet protocol (VoIP) applications produce packets at a deterministic rate but various queuing delays are added to the packets by the network causing packet interarrival jitter. Playout delay prediction techniques schedule audio packets for playout and attempt to make a reasonable compromise between the number of lost packets, the one-way delay and the delay variation since these criteria cannot be optimized simultaneously. In particular, this paper will show that the proposed HMM technique makes a good compromise between the mean end-to-end delay, end-to-end delay standard deviation and average packet loss rate.

A comparative study of the SIP and IAX VoIP protocols

Recently, there has been a strong focus on the development of scalable voice over IP (VoIP) protocols, which are suitable for wide scale deployment. SIP (session initiation protocol) is one such protocol which has been the subject of extensive research over the past few years. More recently, IAX (interasterisk exchange protocol) has emerged as a new VoIP protocol which is steadily gaining credence among the open source community. Among the benefits claimed by the proponents of IAX are its simplicity, NAT-friendliness, efficiency and robustness. This paper makes three key contributions to VoIP research. Firstly, we undertake a comparative evaluation and analysis of the SIP and IAX protocols. Secondly, we report on the viability of utilizing the asterisk PBX as a foundation for conducting research performance studies for VoIP. Finally, we report on live experimental studies of SIP and IAX voice traffic in the Ottawa Metropolitan area. We experimentally studied the performance of voice calls initiated using SIP and IAX for a variety of delay and loss characteristics. In addition, we examined the performance of both protocols in the presence of packet reordering. Our preliminary observations demonstrate that the IAX protocol compares favourably in relation to SIP. More detailed studies are required to evaluate the performance of IAX-based voice traffic in large-scale deployment