What is SOSA
The Sensor Open Systems Architecture (SOSA) Consortium grew out of a U.S. Department of Defense (DoD) initiative to define open standard electronic architectures to ensure component interoperability, reduce costs, encourage innovation, and help to ensure a supply of needed products.
This is not the first time that the aerospace and defense market has attempted to define standards, as ANSI/VITA, SAE International, Radio Technical Commission for Aeronautics, Inc. (RTCA), and others have been used to define system requirements for many years. The SOSA Reference Architecture makes extensive reference to existing standards while further narrowing and defining the requirements into one comprehensive document. This article highlights some of the hardware requirements that differentiate SOSA from VITA VPX.
The SOSA Reference Architecture is specifically intended to support U.S. DoD Command, Control, Communications, Computer, Intelligence, Surveillance, Reconnaissance and Tracking (C4ISRT) systems development. SOSA-aligned architectures are being developed for Communications (Comms), Electro-Optical/Infra-Red (EO/IR), Electronic Warfare (EW), Radar, and Signals Intelligence (SIGINT) systems supporting airborne, subsurface, and space-based mission areas. The referenced requirements and standards define system hardware, interfaces and software.
Note: This article is based on information found in the current SOSA Snapshot, as the baseline SOSA Reference Architecture standard has not yet been released. It is expected to be released later in 2021, and this article will be updated at that time. Until the standard is released products may be “aligned” with the current SOSA Snapshot. After the standard has been released companies will be able to verify whether their products conform to the standard and will be able to apply for SOSA Conformance Certification.
SOSA Hardware Requirements
SOSA requirements for 3U and 6U modules refer extensively to the VITA VPX standards. The SOSA hardware requirements limit some of the VITA options, and require some VITA recommendations.
Future versions of the SOSA Reference Architecture standard may include other form factors, such as a small form factor suitable for Unmanned Aerial Vehicles (UAVs), Drones (both ground and air), Unmanned Underwater Vehicles (UUVs), and Small Satellites.
SOSA limits the power used by the cards to VS1 (12V), 3.3V AUX, and VBAT for primary power.
The VS2 (3.3V) and VS3 (5V) options supported by the VITA standard are not used for SOSA modules.
Maintenance ports on SOSA modules are intended strictly for system maintenance use. They are serial console ports which use RS-232 protocols, but they can be configured for TIA-232 or LVCMOS-level signaling. This allows the ports to be configured to communicate with RS-232 terminals or to a port aggregator or switch using an FPGA.
Maintenance ports on SOSA modules are always in the same location and use a consistent connection approach.
SOSA Slot Profiles
VITA 65 OpenVPX currently provides dozens of 6U VPX and 3U VPX slot profiles, all of which include user defined pins. This results in systems with unique backplanes designed to be used with specific modules.
The SOSA Reference Architecture restricts valid VPX primary slot profiles to a relatively small set of three 6U and six 3U profiles. There are also a number of secondary profiles which are simple variants of the primary profiles. Restricting the number of profiles significantly reduces the possible backplane configurations.
All SOSA profiles have compatible requirements for power plane utilization, data plane protocols, GPIO implementation, maintenance port implementation, and system management.
Only two of the SOSA primary slot profiles have user defined pins, namely the External I/O profiles used to connect to existing aircraft discrete signals.
Cooling and Slot Pitch
Systems being developed for data, image and video processing continue to advance in terms of processing capabilities. Along with that comes ever-increasing demand for power, which in turn increases cooling requirements.
SOSA recognizes the need for advanced cooling methods so that power growth can be accommodated to support future processing needs. In order to accommodate these cooling methods, SOSA has defined slot pitch requirements as 1.00” pitch for conduction and liquid cooled modules, and 1.5” pitch for air flow through modules.
Bandwidth Performance and Connectors
The amount of data processed by modern systems creates a need for increased module and backplane bandwidth. The current SOSA snapshot does not fully define bandwidth requirements, but it does acknowledge that bandwidth requirements are increasing. The expectation is that higher bandwidth requirements will need to be defined for SOSA aligned products.
Many VPX systems use MultiGig RT2 OpenVPX backplane connectors which support up to 12.5 Gbps. This allows these backplane connectors to support up to 10GbE and PCIe Gen3 (8Gbps) bandwidth requirements.
A newer RT3 backplane connector which can support up to 25 Gbps can be used in systems with greater bandwidth requirements. Systems that require support for PCIe Gen4 (16Gbps) or 100GbE (4 lanes of 25 GbE each) will require the newer RT3 connector. The higher bandwidth RT3 connector has also been designed to be backwards compatible with the legacy MULTIGIG RT 2 and RT 2-R connectors.
SOSA backplane connectors can also include those defined in VITA 66, which defines fiber-optic connection modules, and VITA 67, which defines RF and optical connectors which can be used to transmit data at higher bandwidths. Additional connectors may also be considered in the future.
The SOSA standard has requirements or recommendations for other data transmission methods as well. Some of these requirements vary depending on the type of connector or the type of application under consideration. Some examples of these requirements are: network connectors to support Gigabit Ethernet or 10Gig Ethernet, USB 3.1 Gen2, and SATA rev. 3.0.
SOSA Software Requirements
SOSA requirements for the software operating environment includes recommendations for a Run-Time Environment (RTE) which references the FACE Technical Standard amongst others. It is also worth noting that the SOSA RTE specifically excludes GPU programming languages and FPGA firmware. Security, including authentication and authorization, is also part of the SOSA specification.
The VITA VPX standards do not define the software environment, therefore the SOSA RTE recommendations are outside the scope of this article.
SOSA’s Relationship to Other Standards
The U.S. DoD has a strong interest in adoption of several additional relatively new standards: FACE, HOST, CMOSS, MORA, etc. With cooperation between SOSA and these standards committees it should be possible to produce standards that are compatible, with the majority of the requirements being common. If that goal is achieved then products made to conform with SOSA will then be able to conform to one of the other standards with only minor modifications.
SOSA as an Innovation Enabler
Once the SOSA Standard has been released, it will provide embedded systems designers with the ability to rapidly create new systems, and to upgrade existing systems in a fraction of the time currently required. If, as expected, the new standard provides true plug-in card compatibility, it will promote new innovation as system designers will have the ability to plug in modules with new capabilities, confident that the entire system will continue to work without major redesign to accommodate the new module.
For more information about SOSA see https://www.opengroup.org/sosa.