The ccsds spacecraft onboard interface services sois standards an introduction
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The CCSDS Spacecraft Onboard Interface Services (SOIS) Standards An Introduction. Stuart Fowell. 1 st May 2012. Overview. SOIS Standardisation , OSI and SOA SOIS Architecture SOIS Services SOIS Prototyping and Reference Implementation. CCSDS SOIS Standardisation.

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The CCSDS Spacecraft Onboard Interface Services (SOIS) Standards An Introduction

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The CCSDS Spacecraft Onboard Interface Services (SOIS) StandardsAn Introduction

  • Stuart Fowell

1st May 2012


  • SOIS Standardisation, OSI and SOA

  • SOIS Architecture

  • SOIS Services

  • SOIS Prototyping and Reference Implementation

SOIS Introduction

CCSDS SOIS Standardisation

  • The Consultative Committee for Space Data Standards (CCSDS) developing recommendations for communication services onboard a spacecraft, handled by the Spacecraft Onboard Interface Services (SOIS) area

  • SOIS aims to provide a consistent interface to various low-level access methods, enabling a common interface to the application software

    • This is achieved through the providing a uniform set of services over any subnetwork

  • Eventual goal is reusable software that can be easily ported to new missions and run on a range of onboard buses without substantial modification

    • Beyond the uniform set of services over any subnetwork, this goal is to standarise interfaces to devices

  • Late configuration changes, e.g. relocation of thermistor, can be accommodated through simple spacecraft database changes without affecting onboard software

  • Consistent interface should provide an enabler for more complex, higher-level software architectures, e.g. fault-tolerant, distributed, software frameworks and autonomous, onboard mission planners

SOIS Introduction


  • SOIS defined with reference to OSI, similar to aspects of SOA

    • SOIS defined as a layered architecture and services provided by each layer

    • Each service defined in terms of:

      • Service interface offered to higher layers

      • Protocol engine (procedures and PDUs)

        • May include time-outs on receiving PDUs

      • Required services from lower layers

      • Management Information Base (MIB)

      • All defined using structured English

  • Abstract definition, with no reference to implementation in hardware or software, programming languages, APIs etc.

SOIS Introduction

SOIS Architecture

  • Organised into layers:

    • Subnetwork Layer provides access to the Data Link medium and provides a set of SOIS-defined services over the subnetwork defined by that medium

    • Transfer Layeroptionally provides Transport- and Network-layer services based on existing protocols

    • Application Support Layer provides a number of capabilities commonly required onboard a spacecraft

    • Application Layer consists of mission-dependent applications that make use of the SOIS-defined services

  • All managed by Communication Management

SOIS Introduction

Typical subnetwork

Data Link Protocol

Data Link Protocol

Subnetwork =

Physical I/F

Physical I/F

Datalink = Basic communication protocol

Physical = Connector, Pinout, electrical

Data Link Protocol

Data Link Protocol



ECSS Milbus Ext protocol

ECSS Milbus Ext protocol



ECSS SpaceWire Datalink

ECSS SpaceWire Datalink

ECSS SpaceWire Physical

ECSS SpaceWire Physical

SOIS Services

  • SOIS Subnetwork Layer

  • Device Commanding, Data Acquisition & Virtualisation

  • File and Packet Store Access

  • Onboard Time Access

  • Message Transfer

  • Device Plug-and-Play

SOIS Introduction

SOIS Subnetwork Layer

  • Standardise basic communication services to be provided by a subnetwork

    • Services are mapped onto protocols and services provided by different data medium e.g. SpaceWire, MIL-STD-1553B and CAN

    • Not all services need to be provided by a subnetwork type

    • Provision against system requirement should be used to drive subnetwork selection

  • Packet Service – providing packet delivery over a single subnetwork

  • Memory Access Service – providing direct access (memory location read/write, includes block move and read/modify/write) to device memory

  • Synchronisation Service – providing spacecraft time and event synchronisation

  • Test Service – providing establishment of subnetwork functionality and availability

SOIS Introduction

SOIS Subnetwork Layer Mappings

  • MIL-STD-1553B

    • ECSS-E-ST-50-13C, “Interface and communication protocol for MIL-STD-1553B data bus onboard spacecraft”, 15 November 2008

    • Influenced by early drafts of SOIS services

    • Prototype mapping for BCs done by Astrium, RUAG

    • Recommended mapping for BCs and RTs to be produced in SOIS prototype

  • SpaceWire

    • ECSS-E-ST-50-12C, “SpaceWire - Links, nodes, routers and networks”, 31 July 2008

    • ECSS-E-ST-50-51C, “SpaceWire protocol identification”, 5 February 2010

    • ECSS-E-ST-50-52C, “SpaceWire - Remote memory access protocol”, 5 February 2010

    • ECSS-E-ST-50-53C, “SpaceWire - CCSDS packet transfer protocol”, 5 February 2010

    • QoS being addressed in variety of R&D projects, e.g. SpaceWire-RT/T/D protocols from SpaceNet project (University of Dundee)

    • Prototype mappings done by SciSys, UoD

    • Recommended mapping to be produced in SOIS prototype

  • CAN

    • ECSS working group in progress

    • Mapping to SOIS included in WG charter

    • Draft expected end 3Q 2010

SOIS Introduction

Device Commanding, Data Acquisition & Virtualisation

  • Typically used to access spacecraft hardware devices such as sensors and actuators

  • Allows reconfiguration of subsystems (e.g. change location, port etc) or replacement of devices (Star Tracker type A -> B) without affecting users

  • Device Access Service – device-dependant driver providing basic reading from and writing to devices regardless of location

    • Encapsulates device-specific access protocols (protocol and addressing) to devices

    • Mapped onto subnetworks’ Memory Access and/or Packet Services

    • May be driven by Electronic Data Sheets (dynamic or build-time auto-code generation)

  • Device Virtualisation Service – standard device driver providing reference to a device using a virtual, i.e., generic, image of a physical device

    • Standardise device interfaces into classes and associated functions

    • Map class interfaces to actual interfaces – “virtualisation” – device abstraction control procedures

    • May be driven by Electronic Data Sheets (dynamic or build-time auto-code generation)

  • Device Data Pooling Service – maintaining an image of the states of a number of devices

    • Periodic data acquisitions from devices

SOIS Introduction

Device Commanding, Data Acquisition & Virtualisation

SOIS Introduction

File and Packet Store Access

  • Provides access to the spacecraft storage system

    • Encapsulates access methods (protocol and addressing) to storage systems (e.g. mass memories)

    • Can be provided at 2 levels:

      • Network file access protocol, e.g. NFS, mapped onto subnetwork’s Packet Service

      • Remote block storage protocol, e.g. ATA, mapped onto subnetwork’s Memory Access Service, e.g. RMAP, or subnetwork’s Packet Service

  • File Access Service – allows access to files and portions of their contents in local or remote file stores

  • File Management Service – allows management of files and directories in local or remote file stores

  • Packet Store Access Services – allows storage, retrieval and deletion of packets in a local or remote packet store

  • Packet Store Management Services – allows management of packet stores in local or remote packet store systems

SOIS Introduction

File & Packet Store Services

SOIS Introduction

Onboard Time Access

  • Providing access to a local time source

    • Local time source may be synchronised with a master time source using a subnetwork’s Synchronisation Service

  • Time Access Service – providing access to, one-shot alarms and metronomes based on local time source

SOIS Introduction

Message Transfer

  • Discrete message transfer between applications/higher-level services

    • Isolates users from location

    • For inter-processor comms, maps onto subnetwork’s Packet Service

    • For intra-processor comms can use RTOS message queues

  • Four messaging models:

    • Send/receive

    • Query/response

    • Publish/subscribe

    • Announce (similar to multi-cast)

  • Can be used as basis for middlewares/software bus or for inter-partition communication

  • Message Transfer Service – providing application-to-application message exchange

SOIS Introduction

Device Plug-and-Play

  • Plug-and-play of devices

    • Device (and network) discovery

      • E.g. discovery of powered up 1553 RTs or SpaceWire links, routers etc.

    • Management of subnetwork

      • E.g. allocation of addressing, configuration of routing

    • Service discovery

      • E.g. by reading Electronic Data Sheets (xTEDS) from device

    • User notification of discovered devices

  • Subnetwork Device Discovery Service – providing dynamic device recognition

  • Device Enumeration Service – providing support for dynamic spacecraft configuration or enumeration

SOIS Introduction

SOIS Recommendations

  • Latest draft documents can be found in the SOIS working group’s collaborative working environment (CWE)


  • CCSDS SOIS Informational Report, CCSDS 850.0-G-1, June 2007

    • 2nd issue being published in 2012

  • Published as standard:

    • SOIS Subnetwork Packet Service, CCSDS 851.0-M-1, December 2009

    • SOIS Subnetwork Memory Access Service, CCSDS 852.0-M-1, December 2009

    • SOIS Subnetwork Synchronisation Service, CCSDS 853.0-M-1, December 2009

    • SOIS Subnetwork Device Discovery Service, CCSDS 854.0-M-1, December 2009

    • SOIS Subnetwork Test Service, CCSDS 855.0-M-1, December 2009

    • SOIS Time Access Service, CCSDS 872.0-M-1, January 2011

  • Under Publication

    • SOIS File and Packet Store Services, CCSDS 873.0-M-0.1, February 2012

    • SOIS Device Access Service, CCSDS 871.0-R-2.2, April 2012

    • SOIS Device Data Pooling Service, CCSDS 871.1-M-0.1, April 2012

    • SOIS Message Transfer Service, CCSDS 875.0-M-0.1, April 2012

  • About to undergo 1st Agency review:

    • SOIS Device Virtualisation Service, CCSDS 871.2-R-0.2, April 2012

    • SOIS Device Enumeration Service, CCSDS 871.3-R-0.2, April 2012

SOIS Introduction

SOIS Reference Implementation

  • SOIS Reference Implementation Study

    • ESA TRP

    • Jan 2008 – Feb 2009

    • SciSys prime, EADS Astrium sub-contractor

  • Objectives

    • Prototype the SOIS Software Suite within ESA’s RASTA facility

    • Provide feedback on the outcome of the prototyping in order to refine and complete the CCSDS SOIS recommendations

SOIS Introduction

RASTA Test Facility

  • Reference Avionics System Test-bench Activity (RASTA)

  • RASTA OBC supplied by Aeroflex Gaisler

    • LEON2 ASIC (100 MHz) @ ESA or LEON3 FPGA (40 MHz) @ SciSys

    • 3 x SpaceWire links

    • 2 x MIL-STD-1553B BC, RT or BM

    • + others (CAN, Ethernet, UART and Direct I/O)

  • RTEMS 4.6.5 + drivers

  • STARDundee USB-SpaceWire Router & Linux PCs

  • PCI MIL-STD-1553B cards & Linux PCs

SOIS Introduction

SOIS Software Suite Acceptance Testing – Reference Mission

  • Low Cost, Single Instrument, Earth Observation Mission

SOIS Introduction

SOIS Proof of Concept

  • SOIS Proof of Concept Study

    • ESA TRP

    • December 2009 – May 2012

    • SciSys prime, EADS Astrium sub-contractor, Gaisler equipment supplier

  • Objectives:

    • Standardise SOIS APIs

    • Implement all SOIS services, running over SpaceWire and MIL-STD-1553B

      • Inc. mapping onto ECSS-E-ST-50-13C for MIL-STD-1553B (BC and RT)

    • Optimise and characterise implementation of SOIS services on RASTA

    • Integrate SOIS services with other Avionics Components

      • TM/TC Module and Ground Unit, PUS, CFDP

      • SpaceWire-based Advanced Mass Memory & File Store

      • Legacy MIL-STD-1553B Remote Terminal Unit (ACRA Control)

    • Develop SOIS Demonstrator

    • Provide Feedback to CCSDS

SOIS Introduction

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