Andrzej Jajszczyk

Resilience in multilayer networks

The integration of different technologies such as ATM, SDH, and WDM in multilayer transport networks raises many questions regarding the coordination of the individual network layers. Especially in the area of network survivability, much can be gained by a better alignment of the healing actions taken by different network layers in case of outages. Survivability issues encountered in a multilayer environment include, among others: how to identify the original failure cause, how to appoint for each failure a layer responsible for its healing, how to let different layers interwork, and how to provide spare resources in an efficient way.

Quality of service terminology in IP networks

This article provides an overview of commonly used terminology related to quality of service assurance in IP networks. Several approaches to QoS definition, including those of IETF, ITU, and ETSI, are presented and compared. Terms associated with QoS like class of service, grade of service, service level agreement, as well as service level specification (SLS), traffic conditioning agreement (TCA), and traffic conditioning specification (TCS) are discussed. Terminology used in two QoS architectures, IntServ and DiffServ, is also introduced.

QoX: What is it really?

The article puts in order notions related to Quality of Service that are found in documents on service requirements. Apart from presenting a detailed description of QoS itself, it overviews classes of service (CoS) proposed by main standardization bodies and maps them across various transmission technologies. Standards and concepts related to less commonly used, though not less important, terms such as Grade of Service (GoS), Quality of Resilience (QoR), and Quality of Experience (QoE) are also discussed. While provisioning of QoS, CoS, GoS, and QoR is related to various aspects of networking and network performance, QoE describes resulting service features as perceived by the customer. Relations between those intrinsic network features and resulting human-experienced quality are discussed. The above set of QoX terms (where X stands for Service, Experience, etc.) is sufficient to describe and distinguish all aspects of service provisioning.

On Nonblocking Multiconnection Networks

In the paper, four theorems describing conditions under which a three-stage multiconnection network is nonblocking for different routing strategies are formulated and proved. These theorems hold for any values of the structural parameters of a network. For some networks having a small number of outer stage switches, these theorems give significantly lower numbers of required middle stage switches than theorems currently known.

A survey of QoE assurance in converged networks

High user satisfaction with using an application or service is the most meaningful quality evaluation criterion. For this reason the set of issues encompassed by the term quality of experience (QoE), i.e., the quality perceived subjectively by the end-user, is key to Internet service providers, network and software engineers, developers and scientists. From the technical point of view, to assure a high level of QoE, an appropriate level of quality of service (QoS), grade of service (GoS), and quality of resilience (QoR) must be provisioned by the network involved in service delivery. This paper studies QoE provisioning approaches with respect to the following convergence requirements: any service, anywhere, anytime, any user device, any media and networking technology, and by any operator. Challenges related to QoS, GoS and QoR provisioning in converged networks and implications on QoE provisioning are discussed. Convergence between fixed and wireless networks as well as within wireless networks based on different technologies, are considered. A variety of technologies and concepts for future converged networks are discussed.

Nonblocking, repackable, and rearrangeable Clos networks: fifty years of the theory evolution

The article gives an overview of major theoretical issues associated with a switching network structure proposed by C. Clos (1953). The concepts of strict-sense and wide-sense nonblocking as well as repackable and rearrangeable networks are described, showing the development of major research areas. A taxonomy of Clos switching networks and some important results for the basic network structure are given and discussed. Other research issues are enumerated.

Recovery and Its Quality in Multilayer Networks

The paper presents a tutorial on multilayer recovery methods. Emphasis is laid not on their procedural operation, but rather on their quality assessment and differentiation based on reliability parameters (e.g., availability, recovery time) and other relevant features (e.g., affected traffic, state overhead). A brief outline of terminology related to multilayer networks is given. Then, an overview of recovery methods is presented, with focus on multilayer recovery. Next, quality features enabling assessment of multilayer recovery are given along with general approaches to service differentiation based on resilience.

Quality of resilience as a network reliability characterization tool

With the increased role of resilience in modern networks, the existing quality of service is required to be expanded with service availability and maintainability. Recently, studies have shown the strong limitation of the common availability metrics for measuring the users quality of experience. In this article a joint specification of QoS definitions with a sophisticated service resilience characterization is proposed, and a concept called quality of resilience is defined. In this unified performance metric, the frequency and length of service interruption are evaluated. It can be used as a tool for characterization of network reliability, as well as comparison and selection of recovery methods. Additionally, by including it in service level agreements, new and more complex requirements of commercial applications can be guaranteed.

On Nonblocking Switching Networks Composed of Digital Symmetrical Matrices

Significant advances in semiconductor technology make it possible to construct new components called digital symmetrical matrices, which mix in the same integrated circuit, time and space switching. In this paper, structures of multistage nonblocking networks composed of such matrices are described. The condition under which the network will be nonblocking is formulated, and the relationship between the maximal capacity of the network and the number of switching stages is discussed. Formulas for designing optimal threeand five-stage networks are derived. It is shown that general multistage networks should have as few stages as possible for minimizing the cost.

Photonic fast packet switching

Several approaches to photonic fast packet switching systems are presented. The wavelength-, time-, code-, and space-division approaches, including free-space photonic fast packet switching, are discussed. These approaches to photonic fast packet switching systems show that the research in this area is still in its infancy. Among various solutions, those based on a wavelength-division transport network and an electronic controller are most mature.<<ETX>>