Otto Spaniol

Modelling of local computer networks

Abstract This paper presents a new concept for local computer networks. Main features of the new model are: automatic reservations for colliding packets (thus avoiding repeated collisions); near optimum throughput; finite maximum waiting times even for priority scheduling policies. The performance of the system is analyzed by means of a Semi-Markov process. Numerical results have been obtained for the most interesting parameters. A comparison with reservation techniques which have been proposed for other computer networks is given in the final section of the paper.

Analysis and performance evaluation of HYPERchannel access protocols

Abstract HYPERchannel [1,3,5,7] is a local network configuration with random access to the global transmission medium and with ‘Carrier Sense’ techniques. Conflicts are resolved by a fixed priority scheduling of retransmissions. This paper presents a performance evaluation of HYPERchannel access protocols for different types of user systems. Analytical results and asymptotic relations are obtained for the throughput of HYPERchannel under different load characteristics. The fixed priority rule for retransmissions discriminates against low priority users; a modification of the access scheme (‘Fair HYPERchannel’) is proposed which compensates for this undesirable effect. The performance of this new protocol version is also evaluated. In a final section, the access schemes of HYPERchannel are compared with similar access protocols.

Throughput of a satellite channel communication

SummaryThe throughput of a satellite channel communication is depending upon the link protocol. It is well known that the “classical” HDLC protocol is inadequate when applied to satellite links instead of short terrestrial links. Several modifications have been proposed to overcome this problem. The present paper gives an analysis and evaluation of a new class of protocols called “Virtual Subchannel schemes” which splits the satellite link into several components; these subchannels are assigned for transmission in cyclic order and are controlled independently of each other by the classical HDLC procedure.

The Virtual Subchannel Protocol for Satellite Link Communications

HDLC is an internationally accepted link control protocol which has been accepted for terrestrial links. When applied to satellite links, however, HDLC has two major deficiencies: 1. Blocking due to window size limitations. 2. Throughput degradation due to the fact that at most one reject may be outstanding at a given time. Both problems arise as a consequence of the very long signal propagation delay of satellite links.

Satellite Link Communication Protocols

This paper deals with a class of satellite link communication protocols which are based on hierarchical sublayering of the link layer. The new protocols (called ‘virtual subchannel schemes’) may be used in order to overcome the deficiencies of ‘classical’ HDLC when applied to high bandwidth satellite links. The performance of a special protocol version (static virtual subchannel concept) is evaluated by analytical methods.

Lokale Diffusionsnetze mit benutzer- und lastunabhängigem Overhead - C³SMA-Systeme

In den letzten Jahren ist eine Reihe von Protokollen fur die Ubertragung von Daten uber ein gemeinsames Kommunikationsmedium (“multiple-access “-Technik) diskutiert worden. Die einfacheren dieser Protokolle zeichnen sich durch geringen Overhead aus, was durch die Moglichkeit der unbegrenzten Wiederholung von Konflikten erkauft wird. Durch aufwendigere Protokolle kann die Ubertragung konfliktfrei gestaltet werden, jedoch wachst bei den bisher bekannten Verfahren der dabei benotigte Overhead linear mit der Gesamtzahl N der Systembenutzer.