QoS in SpaceFibre and SpaceWire/GigaSpaceWire Protocols

Nowadays SpaceWire, SpaceFibre, GigaSpaceWire protocols are widely used in spacecraft design. SpaceWire is established as one of the main standards for data transmission. It is used in many Russian, European, American and Japanese spacecraft. SpaceFibre is a newly emerging standard for the SpaceWire technology standards family, which is able to operate over fiber-optic and copper cable and supports data rates up to 2 Gbit/s. GigaSpaceWire link specification is also developed for SpaceWire technology extension. It provides gigabit link technology with longer distances and galvanic isolation capability for SpaceWire networks. Quality of service (QoS) becomes important network characteristic for prospective onboard networks. There are various approaches for QoS provision in networks. Some of them provide QoS at every data link and node inside the network, some provide QoS features at the network boundary, in its terminal nodes, some combine these approaches in a way. The SpaceFibre follows the first approach. In every data link it has QoS services, providing priorities, guaranteed bandwidth, guaranteed data delivery, scheduled frames transmission. Implementation of these mechanisms is associated with additional overhead such as frame transmission delay, transmitting overhead information such as header and end of frame, traffic planning and dispatching, retransmission in every data link, etc. These factors lead to increasing overheads and packet transmission time, to useful bandwidth degradation. For SpaceWire/GigaSpaceWire the second approach for QoS provision is evolving. QoS services can be implemented over the basic SpaceWire/GigaSpaceWire network interconnection, e. g. at the Transport layer, with much more economical implementation and overheads. In the article we analyze both approaches, their feasibility and value of QoS in SpaceWire/GigaSpaceWire and in SpaceFibre networks. Networks with different topologies and traffic pattern are used to study and to evaluate the performance. Various traffic types such as the data packets, streaming data, commands will be transmitted in networks. Data delivery characteristics for SpaceFibre and SpaceWire/GigaSpaceWire networks are analyzed and compared.