Livio Lambarelli

A Reconfigurable High-Speed Optical System for Integrated Local Communications

The introduction of optical fibers in local area networks makes it possible to implement wide-band communication systems integrating all the communication services (telephone, data, images, etc.) foreseen in future office scenarios. This paper describes a reconfigurable high-speed local communication system, which is currently under development at the Centro Studi e Laboratori Telecomunicazioni (CSELT), conceived to attain high reliability and efficiency features, therefore suitable for a wide range of application environments, such as automated offices, integrated manufacturing, hospitals, etc. The access organization is based on a hybrid (i.e., circuit and packet) protocol, which guarantees each type of traffic the required grade of service, while allowing an optimal exploitation of the transmission capacity. Fault-tolerance issues are taken as a guideline in the overall system conception and, in particular, in the transmission subsystem design. The transmission subsystem presently uses available optical technology to implement a loop-shaped bus topology capable of reconfiguring by means of a distributed algorithms, when a link or node fails.

Coded Speech in Packet-Switched Networks: Models and Experiments

This paper considers the possibility of introducing packetized voice traffic into a packet-switched network. It is well known that the network must assure voice packets sufficient delay characteristics for conversational speech, i.e., low delay between speaker and listener and low delay jitter or variance. To reach these goals, simplified protocols and priority rules for voice handling are proposed and evaluated. A model of a packet switching node structure capable of handling both data and voice is derived for both analytical and simulation approaches. The use of low bit rate voice encoders is considered. The necessity of avoiding the transmission of silent intervals is discussed in relation to the behavior of packet voice receivers. Proposed strategies are compared by means of analytical tools and simulation experiments considering the presence of voice, interactive, and batch data packets.

Broadening the ATM offer with a full set of service categories

The paper aims at providing a comprehensive picture of the new set of ATM-layer services defined in parallel by the ITU-T and The ATM Forum, outlining the potential benefits that can derive, both to users and network service providers, from the availability of these new functionalities in an ATM-based network. Terminological differences between the ITU-T and ATM Forum documents are compared and clarified and the approaches to the use of quality of service parameters and classes are discussed. The so-called Service Categories (using the ATM Forum nomenclature) are Constant Bit Rate, Variable Bit Rate (VBR), Available Bit Rate (ABR) and Unspecified Bit Rate. The ABR is the newest and the one raising major discussions, as specific congestion control mechanisms, which do represent a real innovation in the ATM framework, have been defined for its support. The paper therefore introduces the ABR service in some details and discusses some still open issues and utilization perspective.

A High-Speed Optical System For Local Area Network

A high-speed optical IAN is described, supporting both stream and packet services. A hybrid multiple access protocol. specifically designed for service integration, is presented along with its main charac teristics. Reliability aspects are examined and solved using a network reconfiguration procedure. The transmission subsystem is analyzed, fixing the main characteristics of the network and highlighting the transmission problems.