Other • 2-D meshes are one of the easiest topologies to visualize – nodes are connected in a “grid” fashion (see Figure). The simple layout also allows many problems to map easily to the structure of this network. 2-D Mesh and 2-D Toroid 2-D meshes have unequal node degree. The node degree...
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3 D Meshes and 3 D Toroids
Other • 3-D meshes and 3-D toroids are similar to 2-D meshes and toroids, except the 3-D mesh/toroid is expanded along the Z-axis to provide another dimensional layer of nodes. In the case of the 3-D toroid, the topmost nodes (along the new Z-axis) are connected to the bottommost nodes (see Figure)....
Acknowledgement and Retransmit
Specification • The receiver shall send a positive acknowledgment (ACK) packet for each DATA packet received without error.
Acronyms
Other • Acronym Definition A/D Analog-to-Digital (as in A/D converter) ACK Acknowledge ADC Analog-to-Digital Converter API Application Program Interface APID Application Identifier APP Application CCC Cube-Connected Cycles CCITT From French: Comité Consultatif International Téléphonique et Télégraphique International Telegraph and Telephone Consultative Committee CC-NUMA Cache Coherent-Non-Uniform Memory Access CCSDS Consultative Committee for Space...
Addressing
Profile • SpaceWire supports three types of addressing: Path (Physical) Addressing, Logical Addressing, and Regional Addressing. JAS uses regional addressing because it provides the greatest flexibility to create scalable networks. Regional addressing uses a two-byte scheme where the first byte identifies the router and the second byte identifies the endpoint address connected...
Advantages of JAS
Other • A modern node-based architecture with reconfigurable node electronics and serial data links between nodes provides the core structure and flexibility needed to enable most of the design strategies. It offers a powerful, yet efficient, modular solution that can be scaled and configured to support payloads of virtually any size and...
Allocation of Service Types and Subtypes
Specification • The PUS provides a standard set of services that are targeted for communication between spacecraft and ground systems. Many of them may not be applicable to on-board communication between applications. However, nothing precludes their use in a JAS-based system. The PUS can be extended to add additional functionality to existing...
Buckling and Crippling
Specification • Evaluation of buckling strength shall consider the combined action of primary and secondary stresses and their effects on general instability, local or panel instability, crippling, and creep.
Buffer Fragmentation and Reassembly
Specification • In cases where a higher-level transmit application (or higher layer in a communications stack) must transmit a buffer of data that exceeds the JRDDP MTU size, the buffer must be fragmented into a series of JRDDP packets and then reassembled at the receive TEP before returning the buffer to the...
Buffer Segmentation and Reassembly
Specification • In cases where a higher-level transmit application, or higher layer in a communications stack, must transmit a buffer of data that exceeds the JEEP MTU size, the buffer must be segmented into a series of JEEP packets and then reassembled at the receive TEP before returning the buffer to the...
CCSDS Telecommand and Telemetry Format Packet Standard
Specification • CCSDS Space Packet The CCSDS packet format consists of a packet primary header and packet data field. The header provides routing information for the packet and metadata that describes the packet. The data field is intended to be a user-defined field that can be customized for applications. Details of how...
Channel Closing Process
Specification • The following sections present the interactions (in the form of UML Sequence Diagrams) between transmit and receive endpoints while closing a channel. Various error conditions are presented in order to show nominal, delayed, and worst case scenarios. The hexagonal icons represent the TEP states while the dashed green lines represent...
Channel Independence
Specification • Each transport channel shall operate independently from other transport channels.
Channel Operations
Specification •
Characteristics
Other • The table below describes the characteristics of JAS. Characteristic Definition Modularity Modular, scalable design capable of accommodating a wide range of applications, complexities and performance needs Configurable Topology Flexible, node-based, topologically configurable architecture that can be easily sized, configured and optimized to meet connectivity and robustness needs of a broad...
Cleanliness
Specification • Cleanliness is an important design consideration which can be mitigated by the mechanical structure and processes. Systems adjacent to an optical payload may have more strict cleanliness requirements than non-optical payload. The following sections describe the requirements which deal with Cleanliness considerations for the JAS mechanical structure.
Coating Surface Resistivity
Specification • The thickness of all chemical film treatments need to be controlled to provide low surface resistivity. Surface resistivity shall be less than 1 x 109 ohm/ square.
Coating Volume Resistivity
Specification • All paints and coatings shall have a volume resistivity less than 1 x 109 ohm-cm.
Coincidence Distribution
Other • The figure below illustrates how the JAS supports intra-payload coincidence and triggering. There are two options: Serial Packets JAS nodes can transmit packetized signals via the communications architecture if latency requirements are not too stringent. Discrete Signals Discrete coincidence and trigger signals can be added to any node through the...
Command and Host Processor Profile
Other • The Command and Host Processor (CH) profile defines a microprocessor-based solution suitable to construct nodes for mission data processing, spacecraft interfaces, and other applications requiring software execution on microprocessor platforms. Nodes based on the CH profile work alongside other nodes within the JAS architecture. The SMAC Profile and the Communication...
Communication Data Links
Specification • JAS nodes should communicate through one or more standard communications protocols. Serial communication protocols are the recommended approach but JAS does not preclude the use of parallel communication protocols. JAS also does not preclude the use of custom or legacy based communications.
Communication Profile
Profile • The Communication Profile defines standard interfaces for facilitating communication between RP, CH, and PS nodes within a JAS system. The Communication Profile focuses primarily on communication between payload applications. It leverages industry standards to support network-based communication using serial interfaces. A common set of communication protocols for space applications has...
Communication Specification
Specification • The Communication Specification provides details about network interfaces, communication services, and packet structures that were described in the Communication Profile. The figure below provides context of where the Communication Specification resides in the JAS standard. JAS Standard Hierarchy
Communications Profile
Other • The Communications Profile defines standard interfaces for facilitating communication between nodes within a JAS system. The Communications Profile focuses primarily on communication between payload applications. It leverages industry standards to support network-based communication using serial interfaces. Adherence to the Communications Profile and Communications Specification is the minimum required for a...
Complete and Incomplete Hypercubes
Other • An overall good performer, hypercubes are very reliable and offer good performance. Complete hypercubes have fixed size of 2^d (i.e., 4, 8, 16, 32, 64, etc, nodes) but an extension to this structure (incomplete hypercubes) allows for arbitrary size. Hypercubes are constructed by beginning with two interconnected nodes (a 1-D...
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