FRUCT #17 20-24 April 2015 Second revision of STP-ISS Transport Yuriy Sheynin, Valentin Olenev, Irina Lavrovskaya, Ilya Korobkov, Saint-Petersburg State University of Aerospace Instrumentation Dmitry Dymov, Sergey Kochura, JSC "Academician M.F. Reshetnev" Information Satellite Systems" Protocol for Spacecraft On-board Networks July 2005 All rights reserved 2005, Alcatel Alenia Space
STP-ISS Interfaces Transport interface Network interface Data SpaceWire packets Applications STP-ISS SpaceWire Link Configuration Control codes Control codes A new transport protocol is being development under the grant agreement between SUAI and JSC ISS. There are two STP-ISS protocol revisions; STP-ISS works on top of SpaceWire Three types of user messages: Control Commands Urgent messages Common messages All rights reserved ISS Reproduction forbidden 2
Features of STP-ISS revisions STP-ISS revision 1 Priority QoS Guaranteed QoS Best effort QoS Connectionless data transmission CRC check Reset & Flush Packet lifetime timer Protocol configuration possibility Maximum data length 2 Kb STP-ISS revision 2 (additionally to rev. 1) Scheduling QoS Connection-oriented data transmission Flow Control Duplicate control commands detection Maximum data length 64 Kb for connection-oriented packets Backward compatibility is provided All rights reserved ISS Reproduction forbidden 3
Application messages Messages encapsulated into the SpaceWire packets; App. Message Transport interface Data length may be: 2 Kbytes for Connectionless data transmission; Header Data EOP STP-ISS packet 64 Kbytes for Connectionoriented data transmission DA STP-ISS header Payload CRC SpaceWire interface CRC-16 is used for protection of both payload and packet header 0 : 42 байта 1 : 2 (64) Кбайт 2 байта Header Data CRC-16 EOP All rights reserved ISS Reproduction forbidden 4
STP-ISS Quality of Service Priority 9 priority levels Main QoS type Data with higher priority should be transmitted first Guaranteed Positive acknowledges for the successful packet transmission Resend timer for each packet Duplicate control commands detection Best Effort No acknowledges Error indication passed to the application Scheduling Single schedule for STP-ISS network nodes Time-code reception beginning of an epoch Each epoch correction of time-slot duration Only the TX side is scheduled All rights reserved ISS Reproduction forbidden 5
Scheduling QoS A single schedule for all SpaceWire nodes working via STP-ISS. Data transmission is possible only during the particular time-slots. Schedule: The number of time-slots in one epoch is not limited The time-code value is not important Beginning of the epoch - time-code reception Time-slot duration correction is performed once an epoch (if needed) Time-slot relevancy window Synchronization if there is significant difference in time-slot duration with Time Master Node 0 Node 1 Node 2 Node 3 Node 4 Node 5 0 1 2 3 4 5 6 7 All rights reserved ISS Reproduction forbidden 6
Transmit Buffering Messages, control commands CRC calculation, packet formatting There are 3 logical buffers for each type of application messages common urgent command Ack rcvd Common packets Urgent packets Command packets Buffers Ctrl send Ack Arbiter SpaceWire packet timers Buffer size recommendation Each buffer should be able to store at list 2 packets All rights reserved ISS Reproduction forbidden 7
Receive buffering Connectionless data Connection-oriented data...... Common message Control Command Urgent message Message 5 Message 2 Message 1 Тransport connection Тransport connection Types of packets from connectionless data transmission are: Application messages Service packets All rights reserved ISS Reproduction forbidden Buffer space reservation is used for connection-oriented data (only for urgent and common messages) Each reserved space can store a few messages 8
Transport connection Virtual simplex connection between two remote nodes (End-to-End) Big data transmission is supported (up to 64 Kb) with minimum overheads: Urgent messages Common messages On-board device #1 Sensors Switch On-board device #0 Processor On-board device #2 On-board device #3 Maximum number of TC 16 transport connections: 8 for transmission 8 for receiving STP-ISS supports Credit-based flow control mechanism All rights reserved ISS Reproduction forbidden 9
Connection establishment Three-phase handshake for connection establishment Connection parameters are specified during the connection establishment There are Timers for each transport connection: Timers for connection establishment and closing Standby timer Application Node #1 Node #2 Open Connection Connection request Connection established Connection confirm Connected We did Тransport Сonnection State Machine for error handling during the connection establishment and closing timer #1 timer #2 STP-ISS STP-ISS timer #3 Connection established Application All rights reserved ISS Reproduction forbidden 10
Flow Control and Duplicate CC detection Flow control mechanism It is used for each transport connection with Guaranteed QoS Each side counts the free buffer space and available credits Available credits are sent in ACKs (or ACK with a special flag) Credits synchronization performs after each N sent packets Duplicate control commands detection Likely not to have duplicate control commands Duplicate control command appears if the ACK is lost RX side stores N last received control commands Each control command has a timer On timer expiration the corresponding control command is deleted from the list of last received commands All rights reserved ISS Reproduction forbidden 11
Recommendations for Hardware implementation of STP-ISS Mandatory implementation includes: Priority QoS (1 priority minimum) Best Effort QoS Transmit buffer (at least for one type of messages) Receive buffer (at least for one type of messages) Possibility to implement RX or TX side only Extentions are: Guaranteed QoS Scheduling QoS Connection-oriented data transmission Duplicate control commands detection All rights reserved ISS Reproduction forbidden 12
Protocol Comparison Required features RMAP PTP STUP JRDDP SpW-D +RMAP Flow control - - - - STP STP-ISS Configuration flexibility - - - - - - Connection-oriented options Data correctness check - - - - - Scheduling QoS - - - - - Priority QoS - - - - Data retransmission - - - - - Acknowledgements - - - All rights reserved ISS Reproduction forbidden 13
Thank you! All rights reserved ISS Reproduction forbidden 14
STP-ISS Modeling and Testing Initial STP-ISS specification Analysis, testing, simulation C++ reference code SDL specification SystemC network modeling STP-ISS rev. 1 specification All rights reserved ISS Reproduction forbidden 15
STP-ISS Modeling and Testing The reference code is intended to be used as the reference for the programmers, who will implement STP ISS in the onboard software. The SDL model is needed for the clear formal description of the STP-ISS internal mechanisms and specification analysis. The SDL specification could be used as a separate document describing the specified mechanisms, and it would be a useful part for the main protocol specification document. The SystemC model shows the STP-ISS protocol operation over SpaceWire network, and it gives an ability to test the network configuration and test networking features. All rights reserved ISS Reproduction forbidden 16