Deterministic services for SpaceWire networks: SpaceWire networks and protocols, long paper

Deterministic behavior is an important paradigm for verification and validation of real-time systems such as those on crewed space vehicles and robotic spacecrafts. Providing deterministic characteristics of the data transfer for the spacecraft that uses the SpaceWire technology is an essential problem, especially for autonomous vehicles like satellites. Deterministic data delivery guarantees that transmission of data from one node of the onboard network to the target node would not take longer than the specified time period. Such task is solved by using specific communication protocols that include a scheduling service. Modern space industry demands a protocol running over SpaceWire, which can provide deterministic data transmission characteristics. The scheduling problem becomes more complicated, when we consider a number of communication protocols simultaneously operating in every node of the network, e.g. RMAP, STP-ISS, CCSDS PTP. Traffic from different transport protocols can interfere especially while getting access to the SpaceWire link in a node. The paper presents Multiprotocol Scheduling Service - a new scheduling protocol for SpaceWire networks which provides deterministic data delivery in a network and performs arbitration of data coming from several transport protocols. Firstly, we give an overview of TDMA-based network protocols that have been developed for the ground-based and onboard networks. Then, we present Multiprotocol Scheduling Service which is based on the STP-ISS scheduling mechanism and extended with additional features.