Packet Addressing

There are two ways of addressing SpaceWire packets: path addressing or logical addressing.

Path Addressing

Path addressing is used to specify the path through a network directly. The leading data character of a packet (the destination identifier) contains the required output port number of the router. For path addressing the leading data character is removed after a router has used it to determine the output port for a packet. If a packet has to pass through several routers to reach its destination then a separate data character is used to specify the output port for each router. Hence if there are three routers to be traversed, three data characters will be needed to specify the destination.

Logical Addressing

Logical Addressing is used to specify the path through a network indirectly via routing tables held in the routers. The leading data character of a packet holds the logical address, which is used to look up the required output port number in the routing table of the router. With logical addressing the leading data character is not normally deleted by the router since the logical address identifies the destination node and will be used by each router encountered on the path to the required destination.