Multichannel Local Area Network Protocols

Multiple-access protocols suitable for packet switching local area networks that use several parallel broadcast channels are presented and analyzed by evaluating their throughput and delay characteristics. The local network architecture is first described, then the network performances are evaluated considering a variety of multiple-access schemes that are derived from CSMA and CSMA-CD protocols, by extending the original single channel schemes to a multiple channel system. It is shown that significant performance improvements are achievable with the multiple channel option. Further advantages obtained with the proposed network architecture are a higher reliability and fault tolerance, and a modular network design that allows a gradual system growth following users' demands.     

Interworking Solutions for a Two-Level Integrated Services Local Area Network

A new generation of integrated services local networks (ISLN's) is needed to yield to local area users the provision of voice, data, and images in a cost-effective manner. Besides high-speed and service integration features, these advanced multiservice communication systems have to also provide powerful interconnection with both public networks and traditional LAN's. So conception and design of the interconnection units, i.e., gateways and bridges, have to be carried out contextually with the network architecture definition. The paper addresses the interworking solutions adopted for a local integrated optical network (LION) currently under development. The architecture of bridges and gateways allowing users belonging to different LION subnetworks to communicate with public networks and commercial systems is also described. In particular, the interconnection with the integrated services digital network (ISDN) is highlighted.     

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.