Improvement of virtual-time CSMA protocol for distributed hard and soft real-time systems on the Ethernet

We present an improvement to the virtual-time CSMA (VTCSMA) protocol for communicating mixed hard and soft real-time messages over an Ethernet. Work has been done on communicating soft real-time messages using the VTCSMA mechanism. Research has shown that this mechanism provides better loss rates compared to the traditional collision-based CSMA/CD protocol. In a real-time system however, hard and soft real time messages coexist. Communication of hard real-time messages needs guarantees on message transfers since a single missed deadline message can lead to system failure which can cause serious damage to the environment or loss of human life. We add a new functionality to the media access control (MAC) layer of the VTCSMA communication system so that hard real-time communication is also possible. We compare the performance of our approach with VTCSMA protocol on a bus-based Ethernet by means of simulation using OMNeT++.