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P2100 SerialPlus: A high performance low-latency scalable interconnect, with no particular limits on bandwidth or distance, suitable for both consumer and industrial applications, such as digital video and audio streams, computer peripheral I/O, computer cluster interconnect, NUMA and ccNUMA multiprocessing.
SerialPlus is designed to make switch hubs and bridges to other standards or to itself as simple as possible, and to support multiple concurrent transfers so that system bandwidth can be expanded, essentially without limits, by adding cables, bridges, and switches.
SerialPlus uses small packets for low latency and for keeping packet buffers inexpensive. "Serial" cables transport these packets one bit at a time, but the same protocols work with wider links as well, which is especially economical for short links (up to about 10m) and for applications that require very high bandwidth (say 500 MBytes/s to multiple GBytes/s per cable).
Current work is adapting SerialPlus for use as an efficient scalable backbone for SerialBus (IEEE 1394) devices, without compromising its future flexibility, scalability, or performance. The difficult parts of this work include the transparent support of SerialBus's initialization across a distributed system, and maintaining isochronous performance guarantees across such systems. The SerialPlus backbone has to be invisible to SerialBus software, so that all the SerialBus devices appear to be on one bus as though they were directly connected.
SerialPlus can be directly and transparently mixed with SerialBus nodes, using small synchronization buffers in the boundary nodes to decouple asynchronous arbitration domains. When more than 63 nodes must be supported, or when it is desirable to decouple one portion of the system from failures or bandwidth hogs of another, bus bridges can be used to replace boundary nodes. At the same time, the SerialPlus system supports a more general interconnection structure (not required to be a nonlooping tree as for SerialBus), and allows all cables to be used independently for concurrent traffic (not limited to one transaction at a time for the entire cabled system).
This SerialPlus backbone will support smooth growth of the digital video and home entertainment markets enabled by SerialBus, all the way from homes up to industrial and commercial studio applications. The SerialPlus architecture is optimized for bridges and switches, which enables arbitrary future growth. Of course, growth to very large systems cannot be completely transparent to SerialBus software; because only 63 devices are possible on a single SerialBus bus, larger systems will require SerialBus device software to handle the possibility of multiple buses, i.e. some devices may need small changes to become bridge aware.
Drafts and slides are updated approximately weekly. (June 2, 1999 update)
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