RapidIO: The Next Generation Communication Fabric For Embedded Application

12.3. VIRTUAL STREAMS

Virtual Streams are defined as an ordered set of protocol data units. The number of streams that might be employed by a system is application specific. A system can have a single stream between an ingress device and an egress device, or it can have a unique stream for every combination of users and traffic types. In the latter case, this could be millions of individual streams. The virtual stream identifier supports up to 4 million streams between any source and any destination in a system.

Figure 12.4. Virtual stream ID

As the figure shows, the VSID is a concatenation of the port address (source or destination) the class of service field, and the streamID field. This means that a RapidIO data streaming system can have 64k unique streams per traffic class, per source - destination pair. The VSID is 'virtual' because it can be overloaded with any meaning required by the application. The destination defines the way the VSID is allocated. The VSID can be associated with specific buffers, or mapped to the physical address of any downstream device at the destination. VSIDs can be used to segregate incoming traffic by protocol or divert traffic to subports. Subports are additional destinations not exposed to the RapidIO fabric address map. The streamID could be used to identify a subport.

The source device is responsible for placing the necessary VSID on a packet ...