The SpaceWire standard defines packets and protocol identifiers. The SpaceWire Logical Layer has the flexibility to utilize standard or customized protocols. There are two classes of protocols available to JAS applications:
- Memory access protocols – access and control memory devices that are located on remote nodes within a network
- Messaging protocols – send arbitrary types of data (messages) between applications
The SpaceWire standard includes one memory access protocol known as Remote Memory Access Protocol (RMAP), which is discussed briefly in this profile. More details can be found in the Communication Specification.
The SpaceWire standard does not inherently include messaging protocols that support the data link convergence functions specified in the SOIS standard; therefore, they were developed for JAS. The messaging protocols are used to encapsulate the data and deliver it to an endpoint using various QoS functions. There are three messaging protocols that are available for use by applications when sending data over SpaceWire.
- JAS Reliable Data Delivery Protocol (JRDDP) – for sending data between applications using a reliable delivery approach.
- JAS Efficient Exchange Protocol (JEEP) – for sending data between applications using a best-effort approach.
- JAS Packet Protocol (JPP) – for sending JAS Packets between applications using a best-effort approach.
The figure below shows each of the messaging protocols and the QoS functions they provide. One additional convergence function was added to the SOIS version of this table. The Data Agnostic function requires that the protocol provides the capability to support different data types. This is accomplished using fields within the protocol packet header which describe the data contents.
All three of the messaging protocols are briefly discussed in this profile. More details can be found in the Communication Specification.