Name of Group | 4.01 Subnetwork Services Working Group |
Area | Spacecraft Onboard Interface Services Area (SOIS) |
Chairperson | Glenn Rakow |
Chairperson E-Mail Address | Glenn.P.Rakow@nasa.gov |
Chairperson Agency | NASA |
Deputy Chairperson | Marco Rovatti |
Deputy Chairperson E-Mail Address | marco.rovatti@esa.int |
Deputy Chairperson Agency | ESA |
Mailing List | sois-subnet@mailman.ccsds.org |
Scope of Activity | The Subnetwork Services Working Group (SUBNET WG) is concerned with the transfer of information onboard a spacecraft between its constituent subsystem components. In practice this involves both hardwired systems and wireless systems.
The mission of the SUBNET WG is to serve as a CCSDS focus group for onboard network technologies. The goals of the WG are to define services and make recommendations pursuant to standardization of applicable data link protocols and related subnetwork services, ensuring inter-operability of independently developed space vehicles and spacecraft onboard networks.
In the past the SUBNET WG has already defined the requirements for information transfer services that must be provided by a subnetwork, along with the service interface provided to higher layers of the communication stack (SOIS Application Support Layer). Considerations for these services included reliable delivery, timeliness, and security that need to be met at the subnetwork layer.
The scope of the SUBNET WG is to perform an overall review of the existing SOIS architecture and Magenta Books. In consultation as necessary with other SOIS WGs, analyze existing service definitions and interfaces, and compare to existing and future mission use cases to determine how well they align. Special attention will be given to distributed systems, software bus, and fault tolerant systems. From this activity, develop a work plan to update any services as necessary to bring existing service books in alignment to an overall coordinated architecture applicable for SOIS and other CCSDS Areas.
It shall further review existing deterministic protocols applicable for space. Define and catalog the deterministic protocols by use cases, and analyze their applicability space. |
Rationale for Activity | During the Onboard Deterministic Network BoF meeting in spring 2015 it was concluded that deterministic networks naturally fit within the domain of the SOIS SUBNET WG. The definition of onboard deterministic subnetwork services may require a number of updates to the SOIS subnetwork Service Magenta book and is therefore best combined with the five-year review of these books. Additionally, during the book review, a mapping of the SOIS Subnetwork services to the most widely used data link types used for on board spacecraft applications will be performed. These mappings will be captured in a SOIS Subnetwork Service Utilization Profile Blue Book.
Five SOIS Subnetwork Service Magenta books have been published in December 2009 and are due for revision or reconfirmation. These include the Subnetwork Packet Service, CCSDS 851.0-M-1; Subnetwork Memory Access Service, CCSDS 852.0-M-1; Subnetwork Synchronization Service, CCSDS 853.0-M-1; Subnetwork Device Discovery Service, CCSDS 854.0-M-1; and Subnetwork Test Service, CCSDS 855.0-M-1. |
Goals | The goals of this Working Group are to:
a) Define deterministic subnetwork services in the form of a SOIS Subnetwork deterministic service magenta book.
b) Perform a five-year review of SOIS Subnetwork Services Magenta Books. This entails analysis of and perform, where necessary, updates to existing SOIS Subnetwork Services Magenta Books based upon the current assessment of requirements for future exploration systems, their relevance to a broad range of requirements for human-rated and robotic missions, and new areas of interest such as deterministic and wireless networks. The following are the published SOIS Subnetwork Services Magenta books for review:
1. Subnetwork Packet Service, CCSDS 851.0-M-1
2. Subnetwork Memory Access Service, CCSDS 852.0-M-1
3. Subnetwork Synchronization Service, CCSDS 853.0-M-1
4. Subnetwork Device Discovery Service, CCSDS 854.0-M-1
5. Subnetwork Test Service, CCSDS 855.0-M-1
The outcome of the review process may result in the addition of new book(s) and, or deletion of existing book(s), as well as updates to existing books. In case that the books are not confirmed but it is concluded that an update is needed the respective CWE Projects will be created and submitted for approval as required.
c) Perform mapping of Subnetwork Services Magenta books to a selected list of data link protocols relevant to spacecraft onboard networks. The mappings will be compiled and published in a new SOIS Subnetwork Services Utilization Profile Blue Book.
It is expected that this effort will involve identifying existing mappings in most cases, but in a very few cases may require creating or leveraging a portion of another specification to create a mapping if it does not already exist. Potential data link protocol candidates for providing the mapping include:
1. CAN
2. Ethernet
3. Mil-Std-1553 (Milbus)
4. RapidIO
5. SpaceFibre (SpFi)
6. SpaceWire (SpW)
7. Time Triggered Ethernet (TTE)
8. Time Triggered Protocol/C (TTP/C)
9. Wireless protocols (various)
d) Provide inputs to the to the Dictionary of Terms (DoT) which is developed by the SOIS Application Support Services WG to define terms that may be used to describe the targeted data link protocols. These would be terms that are specific to a particular data link protocol’s terminology.
|
Survey of Similar Standards Efforts Undertaken in
Other Bodies and elsewhere in CCSDS | The data link protocols used for the mapping are standardized by other bodies like IEEE, ECSS and others. Their mapping to the SOIS service is normally not performed by these standardization bodies. Wherever similar service mapping information is available it will be referred to. |
Patent Licensing Applicability for Future Standards | No limitations on the usage of the planned technologies, patent restrictions or licensing requirements have been identified. |
Technical Risk Mitigation Strategy | With respect to the deterministic networks for safety critical applications, other industries such as commercial aircraft, automobile, rail, etc. are already using these protocols and related architectures for their respective industries. The safety critical concepts are well established for human-rated vehicles but are just beginning to creep into the robotic spacecraft arena to provide gains in integration through more robust composability and fault tolerance. For non-safety critical deterministic networks, spacecraft use them but work is necessary to make interoperability widespread. Hence, the technical risks for these two topic areas are low. The risks center more on resources and ability to educate the appropriate decision makers to see the cost and risk reduction advantages.
For the SOIS SUBNET five-year review, the services have already been defined and prototyped for two onboard data link protocols, SpaceWire and Mil Bus (1553). The mappings for other protocols mostly exist, and where they do not, it is expected that mappings may be adopted soon. The bigger picture is updating the existing books for more advanced architectures that use deterministic networks, and time triggered software in architectures for distributed computing and available computing applications. For this, the technology exists and it is a matter of properly capturing the information, and getting the members of the SUBNET WG up to speed on the technology (if not already). Again, the technical risk is low. |
Management Risk Mitigation Strategy | The main supporting agencies ESA and NASA have demonstrated in the past their long term commitment for long term support for the work in the Spacecraft Onboard Interface Services area and the subnetwork working group.
In addition it is anticipated that supplemental support will be available from sources external to CCSDS, such as Advanced Exploration System (AES) to support to achieve the identified milestones.
The precise amount of the work can only be defined during the 5 year review of the SOIS Subnetwork Services Magenta Books when the level of required updates and changes will be estimated.
It is still expected that a technical team correct composition will be available to complete the identified work in the projected time frame. At this time the members of the revived WG must still be formally appointed pending the confirmation of resources. |
