The basic form of a SpaceWire packet is shown below. More details about SpaceWire packets can be found in the Communication Specification. The format contains the following:
- One or more 8-bit addresses that allow the packet to be routed through the network
- An 8-bit protocol identifier which allows multiple protocols to be simultaneously communicated on the network
- An arbitrary length cargo field that contains the data to be transmitted
- An end of packet designator to mark the end of the packet
A Maximum Transmission Unit (MTU) size, the maximum size of a SpaceWire packet, should be enforced in order to promote fairness. This prevents one endpoint from consuming entire links for long periods of time if they must transmit large quantities of data. MTU size depends on the size of the network and how it plans to be used.