PREDICTABILITY OF MESSAGE TRANSFER IN CSMA-NETWORKS

The paper describes a novel approach to establish predictable message transfer between a set of co-operating nodes controlling a physical process. The protocol allows the coexistence of different classes of criticality in a real-time communication network. The approach exploits a priority scheme to guarantee static preplanned message slots for hard real-time communication and enforces a dynamic earliest deadline first scheduling scheme for SRTMs. Soft real-time or SRTMs can be sent at any time without interfering with the hard real-time traffic. The mechanism is embedded in the media access control (MAC) layer of the communication system and realised by a new variant of the virtual time CSMA (VTCSMA) scheme. One of the benefits of our approach is that it can be applied to all kinds of CSMA-networks including Ethernet and wireless LAN.