Communication Profile

JAS Packet Protocol


The JAS Packet Protocol (JPP) provides the capability to send a single JAS Packet over a SpaceWire data link. JPP is just an encapsulation of a JAS Packet within a SpaceWire packet. Even though it is classified as a SpaceWire protocol, there are no QoS functions provided apart from those that can be obtained from use of the JAS Packet header. JPP is not recommended for most network-based applications because it does not include a segmentation or retransmission capability.

The maximum MTU size of the SpaceWire network must be large enough to accommodate a JAS Packet, approximately 64K bytes, in order to support JPP. Or, a maximum packet size must be imposed for JAS packets. JAS Packets are discussed elsewhere in this profile.

JPP consists of two TEPs, a sender and a receiver, but neither performs any protocol type functions. The sender receives a JAS packet from an application, adds the appropriate SpaceWire packet information, and writes it to the SpaceWire link. The receiver removes the SpaceWire packet information, and returns a JAS packet to the receiving application. Since JAS packets contain a Cyclic Redundancy Check (CRC) as part of their definition, receiving applications can perform some error detection on the data.