JAS Subnetwork Services provide a set of well-defined interfaces for applications to communicate across a network. They provide a layer of abstraction between the applications and the network protocols and data links, thereby allowing applications to be more portable and reusable. The services use a combination of a standard application programming interface (API) and pre-defined configuration data to create this layered architecture. Applications communicate at an abstract level and the subnetwork services begin the process of translating from abstract references to physical references as the data moves down through the communication stack.
JAS currently defines three subnetwork services for use by applications:
- JAS Packet Service – provides a packet-based messaging resource for applications to communicate over a network;
- Memory Access Service – allows applications to remotely communicate with memory-based devices over a network;
- Synchronization Service – allows applications to distribute time or provide event synchronization over a network.
JAS Subnetwork Services are based on the CCSDS SOIS subnetwork services standards. The SOIS standards are specifically written at a high level in order to not assume a specific type of implementation. This allows the specifications to be used in a broader set of systems and software architectures. In order to implement these specifications, some design decisions must be made. The following JAS specifications will describe the services, including the theory of operation, and provide further elaboration on any additional detail that is needed for implementation.
"Spacecraft Onboard Interface Services". CCSDS 850.0-G-2, The Consultative Committee for Space Data Systems (CCSDS), Washington D.C., 2013, Spacecraft Onboard Interface Services.