The Transport Layer defines how transactions are routed from one end point processing element to another through switch processing elements.
The Transport specification describes the header information added to a RapidiIO packet and the way the header information is interpreted by a switching fabric. Every RapidIO endpoint is uniquely identified by a device identifier (ID). Each RapidIO packet contains two device IDs. The first is the destination ID (destID), which indicates where the packet should be routed. The second is the source ID (srcID), which indicates where the packet originated. When an endpoint receives a RapidIO request packet that requires a response, the response packet is composed by swapping the srcID and destID of the request. RapidIO switches use the destID of received packets to determine the output port or ports that should forward the packet. Typically, the destID is used to index into an array of control values. The indexing operation is fast and low cost to implement. RapidIO switches support a standard programming model for the routing table, which simplifies system control.
The Multicast specification provides an additional hardware based capability for duplicating a single message and sending it to multiple selected destinations. The multicast extensions are defined for switches only and end points are largely unaffected. The multicast specification is limited to request transactions that do not require responses such as those described in the Logical I/O specification.